(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\(^{-1}\) ].
Explanation
a)(i) Ion: (Electrically) charged atom or group of atoms formed from an atom by loss or gain of electron.
(ii) Isotopes: Atoms of the same element with the same number of protons but different number of neutrons/Mass number
(b)(i) I. \(_{(12)}\)Mg — 1s\(^2\)2s\(^2\)2p\(^6\)3s\(^2\)
\(_{(13)}\)Al — 1s\(^2\)2s\(^2\)2p\(^6\)3s\(^2\)3p\(^1\)
II. The 3p electron in Aluminium is slightly further away from the nucleus than the 3s electron of magnesium. The shielding / screening effect by the inner electrons is more in Al than in Mg. These two effects outweigh the increase in nuclear charge of Al, hence nuclear attraction for 3s is greater than the 3p.
OR
The 3s outermost orbital in Mg is fully filled and is therefore more stable than the 3p orbital in Al which is neither completely filled nor half-filled and, hence less stable. OR
3s orbital of Mg is close to the nucleus than the 3p orbital of Al, hence the nuclear attraction for the 3s is greater than the 3p.
(ii) Na\(_2\)O, MgO, P\(_4\)O\(_{(10)}\), SO\(_3\), CI\(_2\)O\(_7\), SO\(_2\), Na\(_2\)O\(_2\)
(c)(i) Allotropes are different forms of the same element in the same physical state.
(ii) Diamond and graphite.
(iii) Diamond —For making jewellery.
—For cutting hardly surface materials.
—Making abrassives
(ii) Graphite —As a lubricant.
—For making pencals.
—For making electrodes.
—Neutron moderator.
—Making crucibles.
d)(i) —Colourless.
—Has choking smell.
—Denser than air.
—Fumes in moist air.
—Soluble in water.
(ii) 2NaCl + H\(_2\)SO\(_4\) --> Na\(_2\)SO\(_4\) + 2HCl
OR
NaCl + H\(_2\)SO\(_4\) \(\to\) NaHSO\(_4\) + HCl
e) Mass of W = 5.68mg = 5.68 x 10\(^{-3}\)g
Moles of W = \(\frac{5.68 x 10^3}{28}\)
= 2.03 x 10\(^{-4}\) moles