(a) The electronic configurations of atoms of elements A, B, C and D are given as follows: A. Is\(^2\)2s\(^2\)2p\(^2\); B. 1s\(^2\)2s\(^2\)2sp\(^1\) ; C. 1s\(^2\)2s\(^2\) 2p\(^1\) ; D. 1s\(^2\) 2s\(^2\) (I) Arrange the elements in order of increasing atomic size, giving reasons (ii) State which of the elements I. is divalent II. contains atoms with two unpaired electrons in the grouped state. Ill, readily loses one electron from its atom during chemical bonding IV. belongs to group Ill in the Periodic Table.
(b)(i) State one difference between electrovalent and covalent bonds. (ii) Name two other bonds apart from the ones in (b)(i) above which bind atoms and molecules together. (iii) State two characteristics of a covalent compound.
(c)(i) What is isotopy? (ii) Illustrate with suitable example (iii) Two isotopes of Z with mass numbers 18 and 20 are in the ratio 1:2 Determine the relative atomic mass of Z.
(d)(i) Which of the following elements: calcium, fluorine, iodine neon, magnesium and helium are I. halogens II. noble gases Ill. alkaline earth metals. (ii) Write a balanced equation for the bombardment of \(^7_3Li\) with protons to produce \(^8_4\beta\) and \(\gamma\)-rays (iii) State one use of radioactive isotopes.
Explanation
(a)(i) A (ii) I. D II. A III. B IV. C (b)(i) Electrovalent bond is formed between ions while covalent bond is formed between atoms by sharing electrons or electrovalent bond is formed by mutual transfer of electrons to form ions while covalent bond is formed by sharing electrons. (ii) –Hydrogen bond –Metallic bond –Van der Waal's force –Dative or co-ordinate bond (iii) Characteristics of covalent bond –Low melting and boiling point. –They are soluble in organic solvent –They are mainly molecules –They do not conduct electricity in solution or molten state.
(c)(i) Isotopy is the existence of atoms of the same element with the same atomic number but different mass number due to the number of neutrons. (ii) Hydrogen: \(^1_1H\), \(^2_1H\), \(^3_1H\); Chlorine \(^{35}_{17}Cl\), \(^{37}_{17}Cl\); Carbon: \(^{14}_{6}C\), \(^{13}_{6}C\), \(^{12}_{6}C\) (iii) Relative atomic mass of Z = \(\frac{1}{3}\) x 18 + \(\frac{2}{3}\) x 20 = 6 + 13.33 = 19.33
(d)(i) I. Halogen – Fluorine and iodine II. Noble gases – Neon and helium III. Alkaline earth metals –calcium and magnesium (ii) \(^7_1Li\) + \(^1_4H\)H \(\to\) \(^8 \beta\) + \(\gamma\) (iii) Uses of radioactive isotopes -It is used in radio-carbon dating –It is used in agriculture to produce disease resistant seeds. –It is used in industries to detect leakages in pipes –It is used to treat cancerous growth. –It is used to sterilize surgical equipment.
