(a) Define each of the following terms:
(i) ion; (ii) isotopes.
(b)(i) Consider the:element \(_{12}\)Mg and \(_{3}\)Al
I. Write the electron configuration of each element. II. Explain briefly why the first ionization energy of \(_{12}\)Mg is greater than that of \(_{13}\)Al.
(ii) Write the formulae of three different oxides of period 3 elements that react with water.
(c)(i) What are allotropes?
(ii) Name the two crystalline allotropes of carbon.
(iii) Give one industrial use of each allotrope named in (c)(ii).
(d) On warming crystals of sodium chloride with concentrated tetraoxosulphate (VI) acid, a gas was evolved.
(i) List two physical properties of the gas produced.
(ii) Write a balanced equation for the reaction.
(e) A certain chip W used in a circuit of a microcomputer has a mass of 5.68mg. Calculate the amount of W in the microcomputer. [ W = 28 gmol\(^{-1}\) ].
(a)(i) An ion is an atom or group of atoms that carries a net electrical charge because it has lost or gained one or more electrons. (ii) Isotopes are atoms of the same element having the same atomic number (number of protons) but different mass numbers (different numbers of neutrons).
(b)(i) I. Electron configurations
- 12Mg: 1s2 2s2 2p6 3s2 (2, 8, 2)
- 13Al: 1s2 2s2 2p6 3s2 3p1 (2, 8, 3)
II. The first ionization energy of Mg is greater than that of Al because in Mg the outermost electron is removed from a stable, completely filled 3s2 sub-shell, whereas in Al the outermost electron is removed from the higher-energy 3p sub-shell, which is partly shielded by the 3s electrons and so is more easily removed. Hence less energy is needed for Al.
(ii) Three oxides of period 3 elements that react with water: Na2O, SO3, P4O10.
(c)(i) Allotropes are different structural forms of the same element existing in the same physical state. (ii) Diamond and graphite. (iii) Diamond: used in cutting/drilling tools and as an abrasive; graphite: used as a lubricant and as electrodes.
(d) Warming NaCl with concentrated H2SO4 evolves hydrogen chloride gas.
(i) Two physical properties of HCl: colourless gas; pungent (choking) smell; very soluble in water; fumes in moist air. (ii)
NaCl(s) + H2SO4(l) → NaHSO4(s) + HCl(g)
(e) Amount of W: (5.68 mg = 0.00568 g)
\[ n=\frac{0.00568}{28}=2.03\times10^{-4}\ \text{mol} \]
(a)(i) An ion is an atom or group of atoms that carries a net electrical charge because it has lost or gained one or more electrons. (ii) Isotopes are atoms of the same element having the same atomic number (number of protons) but different mass numbers (different numbers of neutrons).
(b)(i) I. Electron configurations
- 12Mg: 1s2 2s2 2p6 3s2 (2, 8, 2)
- 13Al: 1s2 2s2 2p6 3s2 3p1 (2, 8, 3)
II. The first ionization energy of Mg is greater than that of Al because in Mg the outermost electron is removed from a stable, completely filled 3s2 sub-shell, whereas in Al the outermost electron is removed from the higher-energy 3p sub-shell, which is partly shielded by the 3s electrons and so is more easily removed. Hence less energy is needed for Al.
(ii) Three oxides of period 3 elements that react with water: Na2O, SO3, P4O10.
(c)(i) Allotropes are different structural forms of the same element existing in the same physical state. (ii) Diamond and graphite. (iii) Diamond: used in cutting/drilling tools and as an abrasive; graphite: used as a lubricant and as electrodes.
(d) Warming NaCl with concentrated H2SO4 evolves hydrogen chloride gas.
(i) Two physical properties of HCl: colourless gas; pungent (choking) smell; very soluble in water; fumes in moist air. (ii)
NaCl(s) + H2SO4(l) → NaHSO4(s) + HCl(g)
(e) Amount of W: (5.68 mg = 0.00568 g)
\[ n=\frac{0.00568}{28}=2.03\times10^{-4}\ \text{mol} \]
