Get notes, summary, questions and answers, MCQs, extras, competency-based questions and PDFs of Chemical Bonding: ICSE Class 10 Chemistry (Concise/Selina). However, the notes should only be treated as references, and changes should be made according to the needs of the students.
Summary
Atoms, the tiny building blocks of everything, like to be stable and content. They achieve this by arranging their outermost electrons to be like those of special, very stable atoms called noble gases. To do this, atoms often join with other atoms, forming what we call chemical bonds. This joining happens in a few main ways.
One way atoms bond is by transferring electrons. This is called an electrovalent or ionic bond. Imagine one atom gives away one or more electrons, becoming positively charged (a cation). Another atom accepts these electrons, becoming negatively charged (an anion). These oppositely charged atoms then attract each other strongly, like tiny magnets. Common salt, or sodium chloride, is formed this way. Compounds made with these bonds are usually solid, have high melting and boiling points, and can conduct electricity when melted or dissolved in water because their charged particles can move freely.
Another way atoms bond is by sharing electrons, which is called a covalent bond. Instead of a complete transfer, two atoms share one, two, or even three pairs of electrons. If the sharing is equal, the bond is non-polar, like in hydrogen gas or methane. If one atom pulls the shared electrons more strongly towards itself, the sharing is unequal, creating a polar covalent bond with slight positive and negative parts, like in water or hydrogen chloride. Covalent compounds can be gases, liquids, or soft solids. They usually have lower melting and boiling points and generally do not conduct electricity, though some polar ones can form ions in water.
A special type of covalent bond is the coordinate bond. Here, one atom provides both electrons for sharing, while the other atom simply shares them. This often happens when one atom has a pair of electrons not involved in other bonds, called a lone pair. For example, a water molecule can use one of its lone pairs to bond with a hydrogen ion, forming a hydronium ion. Similarly, an ammonia molecule can form an ammonium ion. These lone pairs can also influence the shape of molecules. When atoms lose electrons, it’s called oxidation, and when they gain electrons, it’s called reduction; these processes always happen together in what are known as redox reactions.
Workbook solutions (Concise/Selina)
Intext Questions and Answers I
1. How do atoms attain noble gas configuration?
Answer: Atoms tend to combine chemically by redistribution of electrons in their outermost shell or valence electrons so that each is left with a stable electronic configuration, which is a duplet or octet. The cause for chemical combination is the tendency of atoms to acquire the nearest noble gas configuration in their outermost orbit and become stable. There are three methods by which atoms can achieve this stable configuration:
(1) The transfer of one or more electrons from one atom to the other to form an electrovalent (or an ionic) bond.
(2) Sharing of one, two or three pairs of electrons between two atoms to form a covalent (or a molecular) bond.
(3) When the shared electron pairs are contributed by only one of the combining atoms, the bond formed is known as a coordinate (or dative) bond.
2. Define: (a) a chemical bond, (b) an electrovalent bond, (c) a covalent bond.
Answer: (a) A chemical bond may be defined as the force of attraction between any two atoms, in a molecule, to maintain stability.
(b) An electrovalent (or an ionic) bond is formed due to the electrostatic force of attraction between a cation and an anion, which are oppositely charged and attract each other.
(c) A covalent (or a molecular) bond is the chemical bond that is formed between two combining atoms by mutual sharing of one or more pairs of electrons.
3. What are the conditions for the formation of an electrovalent bond?
Answer: The formation of cations and anions in an ionic compound depends on the following factors:
- Low ionisation potential: If the ionisation potential of a particular atom is low, it will lose electron(s) easily, meaning a cation is formed easily.
- High electron affinity: If the electron affinity value is high, an anion will be formed easily. A higher electron affinity value favours ionic bonding.
- Large electronegativity difference: If the difference in the electronegativities of two elements is higher, then the transfer of electrons will be easier. Therefore, the greater the difference in electronegativity, the more ionic the nature of the resulting compound will be.
4. An atom X has three electrons more than the noble gas configuration. What type of ion will it form? Write the formula of its (i) sulphate (ii) nitrate (iii) phosphate (iv) carbonate (v) hydroxide.
Answer: An atom X that has three electrons more than the noble gas configuration has 3 valence electrons. Such atoms of metallic elements can lose these electron(s). When a metallic atom loses electron(s), it becomes a positively charged ion, known as a cation. Therefore, atom X will lose its three valence electrons to form a positively charged ion (cation) with a charge of +3, denoted as X³⁺.
(i) Sulphate — X₂(SO₄)₃
(ii) Nitrate — X(NO₃)₃
(iii) Phosphate — XPO₄
(iv) Carbonate — X₂(CO₃)₃
(v) Hydroxide — X(OH)₃
5. Mention the basic tendency of an atom which makes it to combine with other atoms.
Answer: The basic tendency of an atom that makes it combine with other atoms is its tendency to acquire the nearest noble gas configuration in its outermost orbit and become stable. For atoms, stability means having the electron arrangement of an inert gas, i.e., an octet (or duplet for helium) in its outermost shell. To attain this stability, atoms tend to combine chemically.
6. The element X has the electronic configuration 2, 8, 18, 8, 1. Without identifying X, (a) predict the sign and charge on a simple ion of X. (b) write if X will be an oxidising agent or a reducing agent and why.
Answer: (a) The element X has an electronic configuration of 2, 8, 18, 8, 1, which means it has 1 valence electron in its outermost shell. Atoms with 1, 2, or 3 valence electrons tend to lose these electrons to form positively charged ions (cations). Therefore, X will lose its 1 valence electron to achieve a stable electronic configuration. The ion formed will have a positive sign and a charge of +1 (X⁺).
(b) X will be a reducing agent. This is because X loses an electron (undergoes oxidation) to achieve a stable configuration. A reducing agent is a donor of electron(s). Since X donates an electron, it acts as a reducing agent.
7. In the formation of the compound XY₂, an atom X gives one electron to each Y atom. What is the nature of bond in XY₂? Draw the electron dot structure of this compound.
Answer: The nature of the bond in XY₂ is electrovalent (or ionic). This is because the bond is formed by the transfer of electrons from atom X to atom Y; specifically, atom X gives one electron to each of the two Y atoms.
The atom X loses a total of two electrons (one to each Y atom) and forms a cation X²⁺. Each Y atom gains one electron and forms an anion Y⁻. The electron dot structure of the compound XY₂ would show these ions.
8. An atom X has 2,8,7 electrons in its shell. It combines with Y having 1 electron in its outermost shell. (a) What type of bond will be formed between X and Y? (b) Write the formula of the compound formed.
Answer:(a) Atom X has an electronic configuration of 2, 8, 7, meaning it has 7 valence electrons and needs 1 electron to achieve a stable octet. It is a non-metallic element. Atom Y has 1 electron in its outermost shell, which it can lose to achieve a stable configuration. It is a metallic element. Bonds formed between metals and non-metals are typically ionic or electrovalent. Atom Y will lose 1 electron to form Y⁺, and atom X will gain that 1 electron to form X⁻. Therefore, an electrovalent (or ionic) bond will be formed between X and Y due to the transfer of an electron from Y to X.
(b) Since Y forms a Y⁺ ion and X forms an X⁻ ion, the charges balance out in a 1:1 ratio. The formula of the compound formed will be YX.
9. Explain with the help of ionic equation and electron dot structural diagram the formation of the following electrovalent compounds. (i) NaCl (ii) MgCl₂ (iii) CaO
Answer: (i) NaCl
(ii) MgCl₂
(iii) CaO
10. Compare: (a) sodium atom and sodium ion (b) chlorine atom and chloride ion, with respect to (i) atomic structure, (ii) electrical state, (iii) chemical action, (iv) toxicity.
Answer: (a) Sodium atom (Na) and Sodium ion (Na⁺)
The properties of Na are different from Na⁺.
(i) Atomic structure: A sodium atom (Na) has an electronic configuration of 2, 8, 1 with an incomplete outermost shell (1 valence electron). It contains 11 protons and 11 electrons. A sodium ion (Na⁺) has an electronic configuration of 2, 8 with a complete outermost shell. It contains 11 protons but only 10 electrons.
(ii) Electrical state: A sodium atom is electrically neutral. A sodium ion is positively charged (+1).
(iii) Chemical action: A sodium atom is very active. A sodium ion is inactive.
(iv) Toxicity: A sodium atom is poisonous. A sodium ion is non-poisonous.
(b) Chlorine atom (Cl) and Chloride ion (Cl⁻)
The properties of a chlorine atom are different from its ion.
(i) Atomic structure: A chlorine atom (Cl) has an electronic configuration of 2, 8, 7 with an incomplete outermost shell (7 valence electrons). It contains 17 protons and 17 electrons. A chloride ion (Cl⁻) has an electronic configuration of 2, 8, 8 with a complete outermost shell. It contains 17 protons and 18 electrons.
(ii) Electrical state: A chlorine atom is electrically neutral. A chloride ion is negatively charged (-1).
(iii) Chemical action: A chlorine atom is very active. A chloride ion is inactive.
(iv) Toxicity: A chlorine atom (as in Cl₂ gas) is poisonous. A chloride ion is non-poisonous.
11. The electronic configuration of Fluoride ion is the same as that of a neon atom. What is the difference between the two?
Answer: Although both a fluoride ion (F⁻) and a neon atom (Ne) have the same electronic configuration (2, 8), there are significant differences between them:
- Number of Protons and Nuclear Charge: A fluoride ion has 9 protons in its nucleus, resulting in a nuclear charge of +9. A neon atom has 10 protons in its nucleus, resulting in a nuclear charge of +10.
- Overall Electrical Charge: A fluoride ion (F⁻) is an ion and carries a net negative charge of -1 (9 protons, 10 electrons). A neon atom (Ne) is an atom and is electrically neutral (10 protons, 10 electrons).
- Nature and Stability: Neon is an inert gas atom, meaning it is very stable and unreactive under normal conditions. A fluoride ion, while having a stable electronic configuration, is an ion and typically exists as part of an ionic compound or in solution, rather than as an independent gaseous particle like a neon atom.
12. State which of the following are reduction reactions and which are oxidation reactions: (i) Pb → Pb²⁺ + 2e⁻ (ii) Fe²⁺ – e⁻ → Fe³⁺ (iii) Al³⁺ + e⁻ → Al²⁺ (iv) Cu → Cu²⁺ + 2e⁻
Answer: Oxidation involves the loss of electrons, and reduction involves the gain of electrons.
(i) Pb → Pb²⁺ + 2e⁻: Lead (Pb) loses 2 electrons to form Pb²⁺. This is an oxidation reaction.
(ii) Fe²⁺ – e⁻ → Fe³⁺: This can be written as Fe²⁺ → Fe³⁺ + e⁻. The ferrous ion (Fe²⁺) loses 1 electron to form Fe³⁺. This is an oxidation reaction.
(iii) Al³⁺ + e⁻ → Al²⁺: The aluminium ion (Al³⁺) gains 1 electron to form Al²⁺. This is a reduction reaction.
(iv) Cu → Cu²⁺ + 2e⁻: Copper (Cu) loses 2 electrons to form Cu²⁺. This is an oxidation reaction.
13. What do you understand by redox reactions?
Answer: A redox reaction, or redox process, is a chemical reaction in which an electropositive atom undergoes oxidation (loses electrons), while an electronegative atom undergoes reduction (gains electrons). Oxidation and reduction always occur simultaneously in a redox reaction because the electron(s) lost by the reducing agent (the substance that gets oxidized) must be gained by the oxidising agent (the substance that gets reduced).
14. Explain: (i) oxidation and reduction in terms of loss or gain of electrons. (ii) Formation of electrovalent compound is a redox reaction.
Answer: (i) Oxidation and reduction in terms of loss or gain of electrons:
Oxidation is a process that involves the loss of one or more electrons by an atom or ion. For example, when an electropositive atom loses electrons, it undergoes oxidation (e.g., Na → Na⁺ + e⁻).
Reduction is a process that involves the gain of one or more electrons by an atom or ion. For example, when an electronegative atom gains electrons, it undergoes reduction (e.g., Cl₂ + 2e⁻ → 2Cl⁻).
(ii) Formation of electrovalent compound is a redox reaction:
The formation of an electrovalent (or ionic) compound involves the transfer of electrons from one atom (usually a metal) to another atom (usually a non-metal). The atom that loses electrons undergoes oxidation, becoming a positive ion. The atom that gains electrons undergoes reduction, becoming a negative ion. For example, in the formation of sodium chloride (NaCl) from sodium (Na) and chlorine (Cl₂):
Sodium undergoes oxidation: 2Na → 2Na⁺ + 2e⁻
Chlorine undergoes reduction: Cl₂ + 2e⁻ → 2Cl⁻
Since both oxidation (loss of electrons by sodium) and reduction (gain of electrons by chlorine) occur simultaneously, the overall formation of the electrovalent compound NaCl (2Na + Cl₂ → 2Na⁺ + 2Cl⁻ or 2NaCl) is a redox reaction.
15. Divide the following redox reactions into oxidation and reduction half reactions. (i) Zn + Pb²⁺ → Zn²⁺ + Pb (ii) Zn + Cu²⁺ → Zn²⁺ + Cu (iii) Cl₂ + 2Br⁻ → Br₂ + 2Cl⁻ (iv) Sn²⁺ + 2Hg²⁺ → Sn⁴⁺ + Hg₂²⁺ (v) 2Cu⁺ → Cu + Cu²⁺
Answer: (i) Zn + Pb²⁺ → Zn²⁺ + Pb
Oxidation half reaction (loss of electrons): Zn → Zn²⁺ + 2e⁻
Reduction half reaction (gain of electrons): Pb²⁺ + 2e⁻ → Pb
(ii) Zn + Cu²⁺ → Zn²⁺ + Cu
Oxidation half reaction: Zn → Zn²⁺ + 2e⁻
Reduction half reaction: Cu²⁺ + 2e⁻ → Cu
(iii) Cl₂ + 2Br⁻ → Br₂ + 2Cl⁻
Oxidation half reaction: 2Br⁻ → Br₂ + 2e⁻
Reduction half reaction: Cl₂ + 2e⁻ → 2Cl⁻
(iv) Sn²⁺ + 2Hg²⁺ → Sn⁴⁺ + Hg₂²⁺
Oxidation half reaction: Sn²⁺ → Sn⁴⁺ + 2e⁻
Reduction half reaction: 2Hg²⁺ + 2e⁻ → Hg₂²⁺
(v) 2Cu⁺ → Cu + Cu²⁺ (This is a disproportionation reaction where the same species is oxidized and reduced)
Oxidation half reaction: Cu⁺ → Cu²⁺ + e⁻
Reduction half reaction: Cu⁺ + e⁻ → Cu
16. Potassium (at No. 19) and chlorine (at No. 17) react to form a compound. Explain on the basis of electronic concept: (i) oxidation (ii) reduction (iii) oxidising agent (iv) reducing agent.
Answer: Potassium (K), with atomic number 19, has an electronic configuration of 2, 8, 8, 1. It has 1 valence electron.
Chlorine (Cl), with atomic number 17, has an electronic configuration of 2, 8, 7. It has 7 valence electrons.
When potassium and chlorine react, potassium loses its valence electron, and chlorine gains an electron to achieve stable noble gas configurations. The compound formed is potassium chloride (KCl).
(i) Oxidation:
Potassium atom (K) loses its one valence electron to form a potassium ion (K⁺). The loss of electrons is oxidation.
K → K⁺ + e⁻ (Oxidation)
(ii) Reduction:
A chlorine atom (Cl) gains one electron to form a chloride ion (Cl⁻). The gain of electrons is reduction. (If considering diatomic chlorine molecule, Cl₂ + 2e⁻ → 2Cl⁻). For a single atom as implied:
Cl + e⁻ → Cl⁻ (Reduction)
(iii) Oxidizing agent:
The oxidizing agent is the species that accepts electrons and causes the oxidation of another species. In this reaction, chlorine accepts an electron from potassium. Therefore, chlorine is the oxidising agent. An oxidising agent is an acceptor of electron(s).
(iv) Reducing agent:
The reducing agent is the species that donates electrons and causes the reduction of another species. In this reaction, potassium donates an electron to chlorine. Therefore, potassium is the reducing agent. A reducing agent is a donor of electron(s).
Intext Questions and Answers II
1. What are the conditions necessary for the formation of covalent molecules?
Answer: The conditions for the formation of a covalent bond are:
(1) Both atoms should have four or more electrons in their outermost shells, i.e., non-metals (exceptions are H, Be, B, Al, etc.).
(2) Both the atoms should have high electronegativity.
(3) Both the atoms should have high electron affinity.
(4) Both the atoms should have high ionization energy.
(5) The electronegativity difference between the combining atoms should either be zero or negligible.
2. Elements A, B and C have atomic numbers 17,19 and 10 respectively.
(a) State which one is: (i) a non-metal (ii) a metal. (iii) chemically inert?
(b) Write down the formula of the compound formed by two of the above elements.
Answer: (a) Element A (atomic number 17; electronic configuration 2, 8, 7) is (i) a non-metal.
Element B (atomic number 19; electronic configuration 2, 8, 8, 1) is (ii) a metal.
Element C (atomic number 10; electronic configuration 2, 8) is (iii) chemically inert (it is an inert gas, Neon).
(b) The compound formed between element B (metal, forms B⁺ ion) and element A (non-metal, forms A⁻ ion) would be an electrovalent compound. The formula of the compound formed by B and A is BA.
3. Draw electron dot diagram and structure of: (a) nitrogen molecule (b) magnesium chloride (c) methane
Answer: (a) Nitrogen molecule:
(b) Magnesium chloride:
(c) Methane:
4. What is the difference between:
(a) ionic compounds and polar covalent compounds,
(b) ionic compounds and covalent compounds,
(c) a polar covalent compound and a non-polar covalent compound?
Answer: (a) Ionic compounds are formed by the transfer of one or more electrons from one atom to the other, resulting in the formation of ions held by strong electrostatic forces. Polar covalent compounds are formed by the unequal sharing of electron pairs between two atoms, resulting in fractional positive and negative charges on the atoms. Ionic compounds are typically crystalline solids with high melting points and conduct electricity in molten or aqueous states. Polar covalent compounds can exist as gases, liquids, or solids, generally have lower melting points than ionic compounds, and can ionise in water to conduct electricity.
(b) The differences between ionic (electrovalent) and covalent compounds are:
- Nature: Ionic compounds’ constituent particles are ions; they are hard crystalline solids. Covalent compounds’ constituent particles are molecules; they are gases or liquids or soft solids.
- Boiling and melting point: Ionic compounds are non-volatile, with high boiling and high melting points. Covalent compounds are volatile, with low boiling and low melting points.
- Electricity conducting nature: Ionic compounds do not conduct electricity in the solid state but are good conductors in the fused or in aqueous state. Covalent compounds are non-conductors of electricity in solid, molten or aqueous state (though some polar covalent compounds ionize in solution).
- Dissociation/Ionisation: Electrovalent compounds are composed of ions and dissociate in solution or molten state. Covalent compounds (non-polar) do not ionise; polar covalent compounds can ionise in solution.
- Solubility: Ionic compounds are soluble in water but insoluble in organic solvents. Covalent compounds are insoluble in water but dissolve in organic solvents (non-polar covalent compounds).
- Rate of reaction: Ionic compounds show rapid speed of chemical reactions in aqueous solutions. Covalent compounds show slow speed of chemical reactions in aqueous solutions.
(c) A polar covalent compound is formed when the shared pair of electrons are not at equal distance between the two atoms due to a difference in electronegativity, resulting in the development of fractional positive and negative charges. They ionise in water. Examples include HCl and H₂O.
A non-polar covalent compound is formed when the shared pair of electron(s) are equally distributed between the two atoms. These compounds are electrically neutral. This occurs if the two covalently bonded atoms are identical or if their electronegativity difference is little and their structure is symmetrical. Examples include H₂, Cl₂, CH₄, CCl₄. These compounds do not ionise in water due to lack of charge separation.
5. A solid is crystalline, has a high melting point and is water soluble. Describe the nature of the solid.
Answer: The solid is an electrovalent (or ionic) compound. These properties – being a crystalline solid, having a high melting point, and being water-soluble – are characteristic of electrovalent compounds.
6. What do you understand by dipole (polar) molecule? Explain it by taking hydrogen chloride as an example.
Answer: A dipole molecule is a molecule that has both, slight positive and slight negative charge. This occurs in polar covalent molecules where the shared pair of electrons are not at equal distance between the two atoms due to a difference in electronegativity.
In hydrogen chloride (HCl), the strong nuclear charge of the chlorine atom (electronegativity 3) attracts the shared electron pair towards itself. This means the negative charge shifts towards the chlorine atom, thereby developing a slight negative charge (δ⁻) on it. The hydrogen atom (electronegativity 2.1) develops a slight positive charge (δ⁺). Therefore, a polar covalent bond is formed, and HCl is a dipole molecule, represented as Hδ⁺ — Clδ⁻.
7. (a) Explain the bonding in methane molecule using electron dot structure.
(b) Methane molecule is a non-polar molecule. Explain.
Answer: (a) In a methane molecule (CH₄), one atom of carbon shares four electron pairs, one with each of the four atoms of hydrogen. Carbon (electronic configuration [2, 4]) needs four electrons, and hydrogen (electronic configuration [1]) needs one electron to attain stable electronic configurations. Each hydrogen atom shares its one electron with one of carbon’s four valence electrons, forming four single covalent bonds.
The electron dot structure shows carbon at the center with its four valence electrons (represented by dots or crosses) and four hydrogen atoms, each sharing its electron with carbon.
(b) Methane molecule is a non-polar molecule because although the C-H bond has a small polarity due to the slight difference in electronegativity between carbon (2.5) and hydrogen (2.1), the molecule has a symmetrical tetrahedral shape. The shared electron pairs in methane are at nearly equal distance from the carbon and the hydrogen atoms. This symmetrical arrangement causes the individual bond polarities to cancel out, making the molecule as a whole non-polar.
8. Give the characteristic properties of: (a) electrovalent compounds, (b) covalent compounds.
Answer: (a) Characteristic properties of electrovalent compounds:
- Nature: Their constituent particles are ions. They are hard crystalline solids.
- Boiling point and melting point: These are non-volatile, with high boiling and high melting points.
- Electricity conducting nature: They do not conduct electricity in the solid state. They are good conductors of electricity in the fused or in aqueous state.
- Dissociation: Electrovalent compounds are composed of ions. In solution, these ions become mobile. Or in molten state these ions dissociate.
- Solubility: These are soluble in water but insoluble in organic solvents.
- Rate of reaction: They show rapid speed of chemical reactions in aqueous solutions.
- They are good conductors of heat.
(b) Characteristic properties of covalent compounds:
- Nature: Their constituent particles are molecules. These are gases or liquids or soft solids.
- Boiling point and melting point: These are volatile, with low boiling and low melting points.
- Electricity conducting nature: They are non-conductors of electricity in solid, molten or aqueous state (some polar covalent compounds can ionize in solution and conduct).
- Ionisation in solution: On passing electric current, non-polar covalent compounds do not ionise. Some of the covalent compounds are polar in nature and ionize in their solutions.
- Solubility: These are insoluble in water but dissolve in organic solvents (especially non-polar covalent compounds).
- Rate of reaction: They show slow speed of chemical reactions in aqueous solutions.
- They are poor conductors of heat.
9. (a) State the type of bond formed, when the combining atoms have: (i) zero E.N. difference (ii) small E.N. difference (iii) large E.N. difference
(b) State the type of bond formed, and draw Lewis structure of (i) water (ii) calcium oxide
Answer: (a) The type of bond formed when the combining atoms have:
(i) zero E.N. difference (or same electronegativity): non-polar covalent bond.
(ii) small E.N. difference (slightly different electronegativity): polar covalent bond.
(iii) large E.N. difference (much electronegativity difference, more than 1.7): ionic (electrovalent) bond.
(b) (i) Water (H₂O):
Type of bond: Polar covalent bond.
(ii) Calcium oxide (CaO):
Type of bond: Electrovalent (ionic) bond.
10. Explain the following:
(a) Electrovalent compounds conduct electricity.
Answer: Electrovalent compounds conduct electricity because in the fused (molten) state or in aqueous solution, their ions become mobile. These free mobile ions are responsible for carrying the electric current. In the solid state, the ions are fixed in the crystal lattice and cannot move, so they do not conduct electricity.
(b) Electrovalent compounds have high melting and boiling points while covalent compounds have low melting and boiling points.
Answer: Electrovalent compounds have high melting and boiling points because there exists a strong electrostatic force of attraction between the oppositely charged ions. A large amount of energy is required to break this strong bonding force. Covalent compounds have low melting and boiling points because they have weak forces of attraction (van der Waals forces) between the binding molecules, thus less energy is required to break these forces.
(c) Electrovalent compounds dissolve in water whereas covalent compounds do not.
Answer: Electrovalent compounds are generally soluble in water because water, being a polar covalent compound, decreases the electrostatic forces of attraction between the ions, resulting in free ions in aqueous solution. Covalent compounds (specifically non-polar covalent compounds) are generally insoluble in water but dissolve in organic solvents, which are non-polar.
(d) Electrovalent compounds are usually hard crystals.
Answer: Electrovalent compounds are usually hard crystalline solids because their constituent particles are ions, and these ions are held together by strong electrostatic forces of attraction in a well-defined crystal lattice structure, which cannot be separated easily.
(e) Polar covalent compounds conduct electricity.
Answer: Some polar covalent compounds conduct electricity when dissolved in a polar solvent like water because they ionise in their solutions to produce mobile ions. For example, HCl in water ionises to H₃O⁺ and Cl⁻ ions, which can conduct electricity.
(f) Water is a polar covalent molecule.
Answer: Water (H₂O) is a polar covalent molecule because the O-H bonds in it are polarised due to the large difference in electronegativity between oxygen (3.5) and hydrogen (2.1). Oxygen has higher electronegativity, so it attracts the shared pair of electrons towards itself, attaining a slight negative charge (δ⁻), while hydrogen atoms attain a slight positive charge (δ⁺). The molecule has a bent (wedge) shape, and these bond polarities do not cancel out, resulting in an overall polar molecule with distinct positive and negative poles.
11. Elements X, Y and Z have atomic numbers 6, 9 and 12 respectively. Which one:
(a) forms an anion,
(b) forms a cation,
(c) state type of bond between Y and Z and give its molecular formula.
Answer: Element X: Atomic number 6, Electronic configuration [2, 4] (Carbon)
Element Y: Atomic number 9, Electronic configuration [2, 7] (Fluorine)
Element Z: Atomic number 12, Electronic configuration [2, 8, 2] (Magnesium)
(a) Element Y (Fluorine) has 7 valence electrons and needs 1 electron to complete its octet. Therefore, Y forms an anion (Y⁻).
(b) Element Z (Magnesium) has 2 valence electrons, which it tends to lose to achieve a stable octet. Therefore, Z forms a cation (Z²⁺).
(c) Between Y and Z:
Element Z is a metal and will lose 2 electrons to form Z²⁺.
Element Y is a non-metal and will gain 1 electron to form Y⁻.
The type of bond formed will be an electrovalent (or ionic) bond due to the transfer of electrons.
The molecular formula will be ZY₂ (as Z²⁺ combines with two Y⁻ ions to balance the charges).
12. Taking MgCl₂ as an electrovalent compound, CCl₄ as a covalent compound, give four differences between electrovalent and covalent compounds.
Answer: Four differences between electrovalent compounds (like MgCl₂) and covalent compounds (like CCl₄) are:
- Constituent Particles: Electrovalent compounds consist of ions, while covalent compounds consist of molecules.
- Melting and Boiling Points: Electrovalent compounds have high melting and boiling points due to strong electrostatic forces between ions. Covalent compounds have low melting and boiling points due to weak intermolecular forces.
- Electrical Conductivity: Electrovalent compounds conduct electricity in the molten state or in aqueous solution due to mobile ions, but not in the solid state. Covalent compounds are generally non-conductors of electricity in solid, molten, or aqueous states (CCl₄ is a non-conductor).
- Solubility in Water: Electrovalent compounds like MgCl₂ are generally soluble in water. Non-polar covalent compounds like CCl₄ are generally insoluble in water but soluble in organic solvents.
13. Potassium chloride is an electrovalent compound, while hydrogen chloride is a covalent compound. But, both conduct electricity in their aqueous solutions. Explain.
Answer: Potassium chloride (KCl) is an electrovalent compound. When dissolved in water, it dissociates into its constituent ions, K⁺ and Cl⁻, which are free to move and conduct electricity.
Hydrogen chloride (HCl) is a polar covalent compound. When dissolved in water, it undergoes ionisation. The polar HCl molecules interact with polar water molecules, leading to the formation of hydronium ions (H₃O⁺ or H⁺) and chloride ions (Cl⁻). These mobile ions allow the aqueous solution of HCl to conduct electricity. For example: HCl + H₂O → H₃O⁺ + Cl⁻.
14. (a) Draw the electron dot structure of covalent compound methane (non polar) and HCl (polar) and give two difference between them.
(b) Name two compounds that are covalent when taken pure but produce ions when dissolved in water.
(c) For each compound mentioned above give the formulae of ions formed in aqueous solution.
Answer: (a) Electron dot structure of methane (CH₄):
Electron dot structure of HCl:
Two differences between methane and HCl:
- Polarity: Methane is a non-polar covalent compound because of its symmetrical tetrahedral structure and small electronegativity difference between C and H, leading to an overall neutral molecule. HCl is a polar covalent compound due to the significant electronegativity difference between H and Cl, resulting in Hδ⁺ and Clδ⁻.
- Ionisation in Water: Methane does not ionise in water. HCl ionises in water to produce H⁺ (or H₃O⁺) and Cl⁻ ions.
(b) Two compounds that are covalent when taken pure but produce ions when dissolved in water are:
- Hydrogen chloride (HCl)
- Water (H₂O) (through self-ionisation, or when acting as a solvent for other ionising substances like acids) or Ammonia (NH₃).
(c) Formulae of ions formed in aqueous solution:
- For Hydrogen chloride (HCl): H⁺ (or H₃O⁺) and Cl⁻.
- For Water (H₂O) (self-ionisation): H⁺ (or H₃O⁺) and OH⁻.
15. An element M burns in oxygen to form an ionic bond MO. Write the formula of the compounds formed if this element is made to combine with chlorine and sulphur separately.
Answer: If element M forms an ionic compound MO with oxygen, and oxygen typically forms an O²⁻ ion, then M must form an M²⁺ ion to balance the charge.
- When M (as M²⁺) combines with chlorine (which forms Cl⁻ ions), the formula of the compound will be MCl₂.
- When M (as M²⁺) combines with sulphur (which typically forms S²⁻ ions, similar to oxygen), the formula of the compound will be MS.
16. Element A has 2 electrons in its M shell. Element B has atomic number 7.
(a) Write equations to show how A and B form ions.
(b) If B is a diatomic gas, write the equation for the direct combination of A and B to form a compound.
(c) If the compound formed between A and B is melted and an electric current is passed through the molten compound, the element A will be obtained at the ………. and B at the ………. of the electrolytic cell.
Answer: Element A has 2 electrons in its M shell. Its electronic configuration is [2, 8, 2]. It will lose 2 electrons to form A²⁺.
Element B has atomic number 7. Its electronic configuration is [2, 5]. It will gain 3 electrons to form B³⁻.
(a) Equations for ion formation:
A → A²⁺ + 2e⁻
B + 3e⁻ → B³⁻
(b) If B is a diatomic gas (e.g., Nitrogen, N₂), the compound formed between A (A²⁺) and B (B³⁻) will have the formula A₃B₂.
The equation for direct combination is:
3A + B₂ → A₃B₂
(c) In the molten compound A₃B₂, A exists as A²⁺ (cation) and B exists as B³⁻ (anion). During electrolysis:
Element A (A²⁺) will be obtained at the cathode.
Element B (B³⁻) will be obtained at the anode.
17. Element M forms a chloride with the formula MCl₂ which is a solid with high melting point. M would most likely be in the group in which ………. is placed. [(a) Na (b) Mg (c) Al (d) Si.]
Answer: Element M forms a chloride MCl₂, which means M has a valency of +2 and forms an M²⁺ ion. The compound is a solid with a high melting point, characteristic of an ionic compound.
- Na (Sodium) is in Group 1 and forms Na⁺.
- Mg (Magnesium) is in Group 2 and forms Mg²⁺.
- Al (Aluminium) is in Group 13 (or III A) and forms Al³⁺.
- Si (Silicon) is in Group 14 (or IV A) and typically forms covalent compounds like SiCl₄.
Therefore, M would most likely be (b) Mg, which is in Group 2.
18. Complete the following:
Answers:
19. Compound X consists of molecules. Choose the letter corresponding to the correct answer from the options A, B, C and D given below:
(i) The type of bonding in X will be : A. ionic B. electrovalent C. covalent D. molecular
(ii) X is likely to have a: A. low melting point and high boiling point, B. high melting point and low boiling point, C. low melting point and low boiling point, D. high melting point and high boiling point.
(iii) In the liquid state, X will : A. become ionic, B. be an electrolyte, C. conduct electricity, D. not conduct electricity.
Answer: (i) If Compound X consists of molecules, the type of bonding in X will be C. covalent. (The term “molecular bond” is also used for covalent bonds).
(ii) Since X consists of molecules (covalent bonding), X is likely to have a C. low melting point and low boiling point.
(iii) In the liquid state, X (a general compound consisting of molecules, implying covalent) will generally D. not conduct electricity, as covalent compounds typically do not have free ions in the molten state. (Polar covalent compounds may ionize in aqueous solution, but “liquid state” usually refers to the pure molten substance).
Exercise
MCQs
1. The property which is characteristic of an electrovalent compound is that :
(a) it is easily vaporized
(b) it has a high melting point
(c) it is a weak electrolyte
(d) it often exists as a liquid
Answer: (b) it has a high melting point
2. When a metal atom becomes an ion :
(a) it loses electrons and is oxidized
(b) it gains electrons and is reduced
(c) it gains electrons and is oxidized
(d) it loses electrons and is reduced
Answer: (a) it loses electrons and is oxidized
3. Which of the following compounds has all three bonds – ionic, covalent and coordinate bonds ?
(a) Ammonia
(b) Ammonium chloride
(c) Sodium hydroxide
(d) Calcium chloride
Answer: (b) Ammonium chloride
4. Which of the following is not a typical property of an ionic compound ?
(a) High melting point
(b) Conduction of electricity in molten and aqueous states
(c) Insolubility in water
(d) Existence as oppositely charged ions even in the solid state.
Answer: (c) Insolubility in water
5. Metals lose electrons during ionization. This change is called:
(a) Oxidation
(b) Reduction
(c) Redox reaction
(d) Displacement
Answer: (a) Oxidation
6. Compound ‘X’ consists of only molecules. ‘X’ will have:
(a) A crystalline hard structure
(b) Low melting and low boiling point
(c) An ionic bond
(d) A strong force of attraction between its molecules
Answer: (b) Low melting and low boiling point
7. The molecule which contains a triple covalent bond is :
(a) ammonia
(b) methane
(c) water
(d) nitrogen
Answer: (d) nitrogen
8. The formation of a covalent bond between two atoms is favoured when :
P both the atoms have a large difference in electro-negativity
Q both the atoms have high electron affinity
R both the atoms have high electronegativity
(a) Only P
(b) Only Q
(c) Both P and Q
(d) Both Q and R
Answer: (d) Both Q and R
9. Assertion (A): If the electron affinity value is high, anions are formed easily.
Reason (R): Ionic bonding is favoured by high electron affinity.
(a) (1) Both A and R are true and R is the correct explanation of A.
(b) (2) Both A and R are true but R is not the correct explanation of A.
(c) (3) A is true but R is false.
(d) (4) A is false but R is true.
Answer: (b) (2) Both A and R are true but R is not the correct explanation of A.
10. Assertion (A): Atoms can combine either by the transfer of valence electrons from one atom to another or by sharing of valence electrons.
Reason (R): Sharing and transfer of valence electrons is done by atoms to have an octet in their valence shell.
(a) (1) Both A and R are true and R is the correct explanation of A.
(b) (2) Both A and R are true but R is not the correct explanation of A.
(c) (3) A is true but R is false.
(d) (4) A is false but R is true.
Answer: (a) (1) Both A and R are true and R is the correct explanation of A.
11. Assertion (A) : Ionic compounds conduct electricity in molten or aqueous state.
Reason (R): Ionic compounds consist of molecules.
(a) (1) Both A and R are true and R is the correct explanation of A.
(b) (2) Both A and R are true but R is not the correct explanation of A.
(c) (3) A is true but R is false.
(d) (4) A is false but R is true.
Answer: (c) (3) A is true but R is false.
12. Assertion (A) : A pair of electrons not shared with any other atom is known as a lone pair.
Reason (R) : Ammonium ion has a lone pair.
(a) (1) Both A and R are true and R is the correct explanation of A.
(b) (2) Both A and R are true but R is not the correct explanation of A.
(c) (3) A is true but R is false.
(d) (4) A is false but R is true.
Answer: (c) (3) A is true but R is false.
13. Assertion (A): Electrovalent compounds conduct electricity even in solid state.
Reason (R) : Electrovalent compounds are composed of ions.
(a) (1) Both A and R are true and R is the correct explanation of A.
(b) (2) Both A and R are true but R is not the correct explanation of A.
(c) (3) A is true but R is false.
(d) (4) A is false but R is true.
Answer: (d) (4) A is false but R is true.
Very Short Answer Type
1. Fill in the blanks by selecting the correct word from the brackets:
(a) When the nuclei of two different reacting atoms are of ……………… mass, then a bond so formed is called ………………. bond.(equal, unequal, polar, non-polar).
(b) In case of non-polar covalent bond, the covalent bond is formed in the ……………..of atoms and shared electrons are ……………… distributed. (corner, middle, equally, unequally).
(c) Ionic or electrovalent compounds do not conduct electricity in their ………………… state. (fused/solid).
(d) The ions in ………………. compounds are held very strongly due to strong ………………. forces. (electrovalent, covalent, electromagnetic, electrostatic).
(e) In covalent compounds, the bond is formed due to …………….. [sharing/transfer] of electrons.
(f) Electrovalent compounds have a ……………… [low/high] boiling point.
Answer:
(a) When the nuclei of two different reacting atoms are of unequal mass, then a bond so formed is called polar covalent bond.
(b) In case of non-polar covalent bond, the covalent bond is formed in the middle of atoms and shared electrons are equally distributed.
(c) Ionic or electrovalent compounds do not conduct electricity in their solid state.
(d) The ions in electrovalent compounds are held very strongly due to strong electrostatic forces.
(e) In covalent compounds, the bond is formed due to sharing of electrons.
(f) Electrovalent compounds have a high boiling point.
2. Give one word or phrase for the following:
Answer: (a) Formation of ions from molecules: Ionisation.
(b) A bond formed by a shared pair of electrons with both electrons coming from the same atom: Coordinate bond (or dative bond).
(c) A bond formed by a shared pair of electrons, each bonding atom contributing one electron to the pair: Covalent bond.
3. In the formation of magnesium chloride (by direct combination between magnesium and chlorine), name the substance that is oxidized and the substance that is reduced.
Answer: In the formation of magnesium chloride, magnesium (Mg) is oxidized as it loses electrons (Mg → Mg²⁺ + 2e⁻), and chlorine (Cl) is reduced as it gains electrons (Cl + e⁻ → Cl⁻).
4. Give an example in each of the following:
(a) Co-ordinate bond compound:
(b) Solid covalent compound:
(c) Gaseous polar covalent compound:
(d) Gaseous non polar covalent compound:
(e) Liquid non polar covalent compound:
(f) Compound with electrovalent and covalent bond:
(g) Compound with all three types of bonds:
Answer:
(a) Co-ordinate bond compound: Sulphuric acid (H₂SO₄) or Ammonium chloride (NH₄Cl).
(b) Solid covalent compound: SiO₂ (Silicon dioxide) or P₂O₅ (Phosphorus pentoxide).
(c) Gaseous polar covalent compound: HCl (Hydrogen chloride) or Ammonia (NH₃).
(d) Gaseous non polar covalent compound: Methane (CH₄) or Hydrogen (H₂).
(e) Liquid non polar covalent compound: Carbon tetrachloride (CCl₄).
(f) Compound with electrovalent and covalent bond: NaOH (Sodium hydroxide) or CaCO₃ (Calcium carbonate).
(g) Compound with all three types of bonds: Ammonium chloride (NH₄Cl).
5. Electrons are getting added to an element Y.
Answer: (a) Y is getting reduced because it is gaining electrons.
(b) Y will migrate to the anode (positive electrode) during the process of electrolysis, as gaining electrons will make it an anion (negatively charged ion).
Short Answer Type
1. What do you understand by lone pair of electrons.
Answer: A lone pair of electrons is understood as a pair of electrons which is not shared with any other atom.
2. State the type of bonding in the following molecules,
Answer:(a) water (H₂O): Polar covalent bond.
(b) calcium oxide (CaO): Electrovalent (or Ionic) bond.
(c) hydroxyl ion (OH⁻): The bond between oxygen and hydrogen within the ion is a covalent bond.
(d) methane (CH₄): Non-polar covalent bond.
(e) ammonium ion (NH₄⁺): Covalent and Coordinate bonds.
(f) ammonium chloride (NH₄Cl): Ionic, Covalent, and Coordinate bonds.
3. Give reasons:
(a) Hydrogen chloride can be termed as a polar covalent compound
(b) covalent compounds can exist as gases , liquids or soft solids
(c)carbon tetrachloride does not dissolve in water.
Answer: (a) Hydrogen chloride can be termed as a polar covalent compound because in hydrogen chloride, the strong nuclear charge of the chlorine atom (electronegativity 3) attracts the shared electron pair towards itself more than the hydrogen atom (electronegativity 2.1). This results in the chlorine atom developing a slight negative charge (δ⁻) and the hydrogen atom developing a slight positive charge (δ⁺), thus forming a polar covalent bond.
(b) Covalent compounds can exist as gases, liquids or soft solids because their constituent particles are molecules, and they have weak forces of attraction between their molecules.
(c) Carbon tetrachloride does not dissolve in water because covalent compounds, like carbon tetrachloride which is non-polar, are generally insoluble in polar solvents like water. Covalent compounds are insoluble in water but dissolve in organic (non-polar) solvents.
4. There are three elements E, F and G with atomic number 19, 8 and 17 respectively. Give the molecular formula of the compound formed between E and G and state the type of chemical bond in this compound.
Answer: Element E (atomic number 19) has an electronic configuration of 2, 8, 8, 1, so it will form an E⁺ ion (like K⁺). Element G (atomic number 17) has an electronic configuration of 2, 8, 7, so it will form a G⁻ ion (like Cl⁻).
The molecular formula of the compound formed between E and G is EG.
The type of chemical bond in this compound is an electrovalent (or ionic) bond, as it is formed by the transfer of one electron from metal E to non-metal G. Bonds formed between metals and non-metals are typically ionic.
5. A compound is formed between atoms A and B. The electronic configuration of A is 2, 8, 1 and B is 2, 6.
(a) Write the equation of the formation of ions of A and B.
(b) Why do A and B form ions ?
(c) Which of the following can form a compound?
(i) A and A
(ii) A and B
(iii) B and B
Also state the type of bonding present in the compound.
(d) If A and B combines, which of them will get oxidised?
(e) Draw an electron dot diagram of the ionic compound formed in part (c).
(f) Write the formula of the compound formed in part (c) which has a
(i) high melting and boiling point
(ii) gaseous compound
(iii) good conductor of electricity in molten state.
Answer: Atom A (2,8,1) will lose 1 electron to form A⁺. Atom B (2,6) will gain 2 electrons to form B²⁻.
(a) The equations for the formation of ions of A and B are:
A → A⁺ + e⁻
B + 2e⁻ → B²⁻
(b) A and B form ions to attain a stable electronic configuration, specifically the octet configuration of the nearest noble gas, in their outermost shell and become stable.
(c) The following can form a compound:
(i) A and A: Two atoms of metal A would typically form a metallic bond, not an electrovalent or covalent compound as primarily discussed for combinations of different types of elements or non-metals with non-metals.
(ii) A and B: Atom A (metal) and atom B (non-metal) can form an electrovalent (or ionic) compound. The formula would be A₂B.
(iii) B and B: Atom B is a non-metal. Two atoms of B can combine to form a covalent compound (e.g., B₂).
(d) If A and B combine, A will get oxidised because it loses an electron (A → A⁺ + e⁻).
(e)
(f) The formula of the compound formed in part (c):
(i) high melting and boiling point: The electrovalent compound A₂B (formed from A and B) will have a high melting and boiling point.
(ii) gaseous compound: The covalent compound formed from B and B (e.g., B₂) could be a gaseous compound, depending on the nature of B.
(iii) good conductor of electricity in molten state: The electrovalent compound A₂B will be a good conductor of electricity in the molten state.
Long Answer Type
1. Define a coordinate bond and give the conditions for its formation.
Answer: A coordinate bond or dative bond is defined as the bond formed between two atoms by sharing a pair of electrons, provided entirely by one of the combining atoms but shared by both.
The conditions for the formation of a coordinate bond are:
(i) One of the two atoms must have at least one lone pair of electrons, e.g., ammonia (NH₃), water (H₂O).
(ii) Another atom should be short of at least a pair of electrons, e.g., Hydrogen ion (H⁺).
2. Draw an electron dot diagram for the formation of each of the following: State the type of bonding present in them.
Answer: (a) Hydronium ion (H₃O⁺):
Types of bonding present: Two single covalent bonds (O-H) and one coordinate bond (O→H).
(b) Ammonium ion (NH₄⁺):
Types of bonding present: Three covalent bonds (N-H) and one coordinate bond (N→H).
(c) Hydroxyl ion (OH⁻):
Type of bonding present: One covalent bond (O-H) within the ion.
3. (a) How many atoms of each kind are present in the following molecules : calcium oxide, chlorine, water and carbon tetrachloride ?
Answer: (a) Atoms of each kind present are:
Calcium oxide (CaO): 1 calcium atom, 1 oxygen atom.
Chlorine (Cl₂): 2 chlorine atoms.
Water (H₂O): 2 hydrogen atoms, 1 oxygen atom.
Carbon tetrachloride (CCl₄): 1 carbon atom, 4 chlorine atoms.
(b) How many electrons are required or released by each atom mentioned in (a) to attain the nearest noble gas configuration?
Answer: (b) Electrons required or released:
Calcium (in CaO): Releases 2 electrons.
Oxygen (in CaO or H₂O): Requires 2 electrons (by gaining or sharing).
Chlorine (in Cl₂ or CCl₄): Requires 1 electron (by sharing, or gaining to form an ion).
Hydrogen (in H₂O): Requires 1 electron (by sharing for duplet).
Carbon (in CCl₄): Requires 4 electrons (by sharing).
4. Acids dissolve in water and produce positively charged ions. Draw the structure of these positive ions.
Answer: When acids dissolve in water, they release hydrogen ions (H⁺). These H⁺ ions combine with water molecules (H₂O) to form positively charged hydronium ions (H₃O⁺). The H⁺ ion adds on to one of the two lone pairs of electrons of the oxygen atom of the water molecule forming a coordinate bond.
The structure of the hydronium ion (H₃O⁺) is:
5. (a) Elements Q and S react together to form an ionic compound. Under normal condition, which physical state will the compound QS exist in ?
Answer: (a) Under normal conditions, the ionic compound QS will exist in a solid state, as electrovalent (ionic) compounds are typically hard crystalline solids.
(b) Can Q and S, both be metals? Justify your answer.
Answer: (b) No, Q and S cannot both be metals if they form an ionic compound through the typical electron transfer mechanism.
Justification: Ionic bonds are generally formed by the transfer of electrons from a metallic element (which tends to lose electrons to form a cation) to a non-metallic element (which tends to gain electrons to form an anion). If both Q and S were metals, they would both have a tendency to lose electrons, rather than one losing and the other gaining to form an ionic bond.
6. Draw the structural formula of carbon tetrachloride and state the type of bond present in it.
Answer: The structural formula of carbon tetrachloride (CCl₄) shows one carbon atom bonded to four chlorine atoms.
The type of bond present in carbon tetrachloride is covalent bond. Specifically, there are four single covalent bonds, where one atom of carbon shares four electron pairs, one with each of the four atoms of chlorine.
7. Compare carbon tetrachloride and sodium chloride with regard to solubility in water and electrical conductivity.
Answer: Carbon tetrachloride (a covalent compound) and sodium chloride (an electrovalent compound) can be compared as follows:
a. Solubility in Water:
(i) Sodium chloride: It is soluble in water. As water is a polar compound, it decreases the electrostatic forces of attraction in sodium chloride, resulting in free ions in aqueous solution, hence it dissolves.
(ii) Carbon tetrachloride: It is insoluble in water. Covalent compounds like carbon tetrachloride (which is non-polar) are generally insoluble in water but dissolve in organic solvents.
b. Electrical Conductivity:
(i) Sodium chloride: It is a good conductor of electricity in the fused (molten) or in aqueous state due to the presence of free mobile ions. In the solid state, it does not conduct electricity because the ions are fixed.
(ii) Carbon tetrachloride: It is a non-conductor of electricity in solid, molten, or aqueous state. This is because solutions of covalent compounds like carbon tetrachloride contain only molecules and no ions.
8. Draw an electron dot diagram of hydronium ion. State the type of bonding present in it.
Answer: The electron dot diagram for the formation of a hydronium ion (H₃O⁺) from a water molecule and a hydrogen ion (H⁺) is as follows:
The types of bonding present in a hydronium ion are:
a Two single covalent bonds (between oxygen and two hydrogen atoms, originally from the water molecule).
b. One coordinate bond (formed when the oxygen atom of water donates its lone pair to the hydrogen ion).
The hydronium ion has a lone pair, two single covalent bonds, and one coordinate bond.
9. By drawing an electron dot diagram, show the lone pair effect leading to the formation of – ammonium ion from ammonia gas and hydrogen ion.
Answer: The formation of an ammonium ion (NH₄⁺) from ammonia (NH₃) and a hydrogen ion (H⁺) showing the lone pair effect is as follows:
The nitrogen atom in an ammonia molecule contains a lone pair of electrons. This ammonia molecule combines with a hydrogen ion (H⁺), which has no electrons, in such a way that the lone pair of electrons on the nitrogen atom is shared by the hydrogen ion. This bond formed between the nitrogen atom in ammonia and the hydrogen ion is a coordinate bond. Once this bond is formed, all four N-H bonds become identical.
10. Study the extract of the Periodic Table given below and answer the questions that follow. Give the alphabet corresponding to the element in question. DO NOT repeat an element.
Answer: (a) Which element forms an electrovalent compound with G?
E (A halogen from Group 17, like E, will form an electrovalent compound with a Group 1 metal, like G, e.g., GE). Also, D (a chalcogen from Group 16) can form an electrovalent compound with G (e.g., G₂D).
(b) The ion of which element will migrate towards the cathode during electrolysis ?
The ions of A, B, C, or G will migrate towards the cathode, as these elements are metals and will form positive ions (cations). (The question asks for “which element”, singular. Any of these would be correct as they form cations).
(c) Which non-metallic element has the valency 2?
D (Element D is in Group 16, and non-metals in this group typically have a valency of 2, e.g., oxygen, sulfur).
(d) Which is an inert gas ?
F (Element F is in Group 18, which contains inert or noble gases).
11. The following table shows the electronic configuration of the elements W, X, Y and Z.
Answer: (a) What type of bond is formed between :
1. W and X: W (2,8,1) is a metal, and X (2,8,7) is a non-metal. An electrovalent (or ionic) bond is formed between W and X by the transfer of one electron from W to X.
2. Y and Z: Y (2,5) is a non-metal, and Z (1) is a non-metal (typically hydrogen). A covalent bond is formed between Y and Z by the mutual sharing of electrons.
(b) What is the formula of the compound formed between :
1. X and Z: X has 7 valence electrons (needs 1, valency 1). Z has 1 valence electron (needs 1 or shares 1, valency 1). The formula will be XZ (or ZX). (e.g., if X is Cl and Z is H, then HCl).
2. W and X: W has 1 valence electron (loses 1, valency 1, forms W⁺). X has 7 valence electrons (gains 1, valency 1, forms X⁻). The formula will be WX. (e.g., if W is Na and X is Cl, then NaCl).
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