(a) The electronic configuration of five elements represented by the letters P, Q, R, S and T are indicated below.
P – 1s(_2)2s(_2)2p(_2)
Q 1s(_2)2s(_2)2p(_4)
R 1s(_2)2s(_2)2p(_6)
S – 1s(_2)2s(_2)2p(_6)3s(_2)
T – 1s(_2)2s(_2)2p(_6)3s(_2)3p(_5)
without identifying the elements, state which of them
(i) belongs to group VI in the periodic table;
(ii) is strongly metallic in character;
(iii) readily ionizes by gaining one electron;
(iv) contains two unpaired electrons in the ground state atom
(v) readily loses two electrons during chemical bonding
(vi) Does not paricipates in chemical reactions?
(vii) is an s-block element.
(b)(i) Copy and complete the table below as appropriate
| Particle | Number of Protons | Number of Electrons | Number of Neutrons |
| (^1_1H) | 1 | 1 | |
| (^{27}_{13})Al(^{3+}) | |||
| (^{16}_{8}O^{2+}) | 8 |
(ii) Give the reason why atomic radius increases down a group in the periodic table but decreases from left to right in a period.
(c)(i) What is meant by the half-life of a radioactive element?
(ii) The nuclide (^{210}_{84}PO) loses an alpha 4° particle to form lead. Write an equation for the reaction.
(d) State the type of chemical bonding which accounts for each of the following observations:
(i) Chlorine exists as discrete molecules
(ii) Sodium chloride dissolves readily in water;
(iii) CuSO(_{4(aq)}) forms a deep blue complex ion with excess NH(_{3(aq)})
Explanation
(a)(i) Q belongs to group VI in the periodic table.
(ii) S is strongly metallic in character
(iii) T readily ionizes by gaining one electrons
(iv) P and Q contain two unpaired electrons in the ground state atom;
(v) S readily loses two electrons during chemical bonding
(vi) R does not participate readily in chemical reactions
(vii) S is an s-block element.
(b)
| Particle | Number of Protons | Number of Electrons | Number of Neutrons |
| (^1_1H) | 1 | 1 | 0 |
| (^{27}_{13})Al(^{3+}) | 13 | 10 | 14 |
| (^{16}_{8}O^{2+}) | 8 | 10 | 8 |
(ii) Atomic radius-increases down a group in the periodic table but decreases from left to right across a period, because as atomic number/ number of electrons increases down a group, number of shells increases, hence atomic size increases. Across a period the number of electrons and protons also increases but there is no increase in the number of shells/ the electrons are added to the same shell. The resultant effect is that the electrons in the orbit experience a greater pull towards the nucleus/ effective nuclear charge increases resulting in decrease in size.
(c)(i) The half-life of a radioactive element is the time taken for half of the total number of atoms in a given sample of the element to decay.
(ii) (^{210}_{84}PO) (to) (^{206}_{82}PO) + (^{4}_{2}He)
(d) The type of chemical bonding that accounts for the following observations:
(i) Chlorine exists as discrete molecules-covalent
(ii) Sodium chlorine dissolves readily in water-ionic/electrovalent
(iii) CuSO(_{4(aq)}) forms a deep blue complexion with excess NH(_3) –coordinate covalent/dative.