Question

(1)Using the Periodic Table, predict the formulas of compounds which might be formed by the following pairs of elements;
$A)$ Silicon and bromine

(2)Using the Periodic Table, predict the formulas of compounds which might be formed by the following pairs of elements;
$B)$ Aluminium and sulphur

Answer 1

$A)$ Electronic configuration

$Si\Rightarrow 1s^{2}2s^{2}2p^{6}3s^{2}3p^2$

$Br\Rightarrow 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{2}4p^5$

Valency of the element
Valency of an element is the number of electrons which an atom of element loses or gains or shares during a chemical reaction in order to complete its octet.

$\Rightarrow$ The silicon atom prefers to gain or lose $4$ electrons to make stable compound. So, it is tetravalent.

Hence, the valency of $Si=4$

$\Rightarrow$ The bromine atom prefers to gain an electron rather than losing $5$ electrons to make stable compound thus it monovalent.

Hence, valency of $Br$ is $1.$


Hence, formula of the compound, which can be formed by the $Si\&Br$ is $SiB{r}_4.$

Final Answer: Formula of the compound: $SiB{r}_4.$


$B)$ Electronic configuration

$Al\to 1s^{2}2s^{2}2p^{6}3s^{2}3p^1$

$S\Rightarrow 1s^{2}2s^{2}2p^{6}3s^{2}3p^4$

Valency of the element

Valency of an element is the number of electrons which an atom of element loses or gains or shares during a chemical reaction in order to complete its octet.

$\Rightarrow$ The Al atom prefers to lose $3$ electrons to make stable compound, thus it is trivalent.

Hence, the valency of $Al=3$

$\Rightarrow$ The sulphur atom prefers to gain $2$ electrons to make stable compound.

Hence, the valency of $S=2$

Valency:


Hence, formula of the compound which can be formed by the ${}^{\prime }A{l}^{\prime }\&S$ is $A{l}_2{S}_3$

Final Answer: Formula of the compound is $A{l}_2{S}_3.$