Chapter 9 Solutions — Atomic Foundations of Matter

Revise, Reflect, Refine

1. 1.
   A particular element (A) has one electron in its third shell. There is another element (B) with six electrons in its second shell.

   • (i) How many electrons does A tend to give or take to become stable?
   • (ii) What kind of ion would it form?
   • (iii) How many electrons does B tend to give or take to become stable?
   • (iv) What kind of ion would it form?
   • (v) If A and B were to combine, what kind of bond…
2. 2.
   An element X has six electrons in its outer shell and forms a diatomic molecule.

   • (i) Why would that be so?
   • (ii) What kind of bond would it form?
   • (iii) Draw the structure of the molecule it would form.
   • (iv) A certain other element Y has two electrons in its second shell. Draw the structure of the molecule that X would form with Y.
3. 3.
   You want to design a new ionic compound where the total positive charge is 6+ and the total negative charge is 6−. Which of the following combinations gives the correct number of ions?

   • (i) 2 Al³⁺ and 3 Cl⁻
   • (ii) 3 Mg²⁺ and 1 PO₄³⁻
   • (iii) 2 Fe³⁺ and 3 O²⁻
   • (iv) 3 Ca²⁺ and 2 SO₄²⁻
4. 4.
   Choose the correct statement(s) and correct the false statement(s).

   • (i) Elements are made up of molecules and compounds are made up of atoms.
   • (ii) The molecule of a compound is always made up of two or more atoms of the same kind.
   • (iii) One molecule of nitrogen gas contains three nitrogen atoms.
   • (iv) Water is made of two hydrogen atoms, covalently bonded with one oxygen atom.
5. 5.
   Write the chemical formulae for the following compounds.

   • (i) Aluminium nitrate
   • (ii) Calcium oxide
   • (iii) Ferric oxide
6. 6.
   Write the formulae of the compounds formed from the following pairs of ions.

   • (i) Ca²⁺ and Br⁻
   • (ii) Al³⁺ and CO₃²⁻
   • (iii) K⁺ and SO₄²⁻
   • (iv) NH₄⁺ and Cl⁻
7. 7.
   Which of the following, in Fig. 9.18, correctly represents Cl⁻ ion (Atomic number of chlorine = 17)?
8. 8.
   Determine the formula unit mass of the following substances.

   • (i) Ammonium nitrate (NH₄NO₃), used as a nitrogen fertiliser, which is essential for plant growth.
   • (ii) Phosphoric acid (H₃PO₄), used to make phosphate fertiliser and detergents.
   • (iii) Sodium hydrogencarbonate (NaHCO₃), used to relieve acidity and helps in digestion.
9. 9.
   Write the formulae for the compounds formed by the reaction of:

   • (i) Magnesium and nitrogen
   • (ii) Lithium and nitrogen
   • (iii) Sodium and sulfur
   • (iv) Aluminium and oxygen
10. 10.
    Complete Table 9.3 by writing the formulae of the compounds formed by the cations on the left and the anions at the top. LiNO₃ is given as an example. Cations: NH₄⁺, Li⁺ (example: LiNO₃), Al³⁺, Cu²⁺ Anions: NO₃⁻, SO₄²⁻, PO₄³⁻
11. 11.
    5.3 g of sodium carbonate and 6.0 g of acetic acid react to produce 2.2 g of carbon dioxide, 0.9 g of water, and 8.2 g of sodium acetate. Verify whether the law of conservation of mass is valid.
12. 12.
    If a species has 11 protons, 12 neutrons and 10 electrons then:

    • (i) what is its atomic number and mass number?
    • (ii) is it neutral, a cation or an anion? Explain.
    • (iii) write its electronic configuration.
    • (iv) name the species.
13. 13.
    Two elements, A and B, have the following configurations — A: 2, 8, 5 and B: 2, 8, 7.

    • (i) Which element is more reactive?
    • (ii) Will A and B form ionic or covalent bonds when they combine? Explain using electron transfer or sharing.
    • (iii) Predict the formula of the compound they would form.
14. 14.
    Assertion (A): Copper sulfate conducts electricity in the molten state but not in the solid state. Reason (R): Copper and sulfate ions are fixed in the lattice in molten state, while in solid state they can move freely. Choose the correct option:

    • (i) Both A and R are true, and R is the correct explanation of A.
    • (ii) Both A and R are true, but R is not the correct explanation of A.
    • (iii) A is…
15. 15.
    The species ²⁷Al, ⁸⁰Br⁻ and ²⁰¹Hg²⁺ have 13, 35 and 80 protons, respectively. How many electrons and neutrons do they have?