Question

(a) Are the oxidation state and covalency of Al in [AICI(H₂O)₅]²⁺+  same?

(b) Which of the following will have the most negative electron gain enthalpy and which the least negative? P,S, C1, F

Explain your answer.

(c) Using the Periodic Table, predict the formulas of compounds which might be formed by the following pairs of elements:

(i) Si and Br

(ii) Al and S

Answer 1

(a) No, the oxidation state of Al is +3 and the covalency is 6.

(b) Electron gain enthalpy generally becomes more negative across a period as we more from left to right. Within a group, electron gain enthalpy becomes less negative down a group. However, adding an electron to the 2p-orbital leads to more repulsion than adding an electron to the larger 3p-orbital. Hence, the element with most negative electron gain enthalpy is CI and the one with the least negative electron gain enthalpy is P

(c) (i) Si is a group 14 element with a valence of 4; Br belongs to the halogen family with a valence of 1. Therefore, the formula of the compound formed would be SiBr₄.

(ii) Al belongs to group 13 with a valence of 3, S belong to group 16 elements with valence of 2. Therefore, the formula of the compound formed would be Al₂S₃.