Question

Predict the formula of a compound formed by aluminum and sulfur.
(A) ${ Al }_{ 2 }{ S }_{ 2 }$
(B) ${ Al }_{ 3 }{ S }_{ 2 }$
(C) ${ Al }_{ 2 }{ S }_{ 3 }$
(D) AlS

Answer 1

Hint: Valency is defined as the combining capacity of an element. The electrons present in the outermost most shell of an atom are known as valence electrons and they determine the valency. The valence electrons take part in a chemical reaction and they determine the chemical properties of the elements.

Complete step-by-step answer:
The atomic number of Al = 13
So, the electronic configuration of Al will be $\left[ Ne \right] { 3s }^{ 2 }{ 3p }^{ 1 }$
Hence, the valency of aluminium = 3
Similarly, the atomic number of S = 16
So, the electronic configuration of S will be $\left[ Ne \right] { 3s }^{ 2 }{ 3p }^{ 4 }$
Hence, the valency of sulfur = (8-6) = 2
Al loses three electrons to form ${ Al }^{ +3 }$ ion whereas S gains two electrons and forms ${ S }^{ 2- }$ ion.
Now, two ${ Al }^{ +3 }$ ions combine with three ${ S }^{ 2- }$ ions to form ${ Al }_{ 2 }{ S }_{ 3 }$.

Hence, the correct option is C.

Additional Information:
* The number of valence electrons of components increments from left to right in the periodic table.
* On the off chance that the no of valence electrons is not exactly or equivalent to 4; at that point valency is equivalent to no. of valence electrons.
* In the event that the no of valence electrons more than 4; at that point valency = 8 – no.of valence electrons.
* This does not include transition metals as they do not change the no. of valence electrons.

Note: The possibility to make a mistake is that you may not cross multiplying the valency of aluminum and sulfide but instead they could just take their individual valencies and use them as subscripts.