Question

Write the atomicity of the following:
(i) Sulphur
(ii) Phosphorus

Answer 1

Hint: The total number of atoms in a molecule is known as atomicity. The term atomicity is often used interchangeably with the term valency. It can also be measured as the ratio of molecular mass to atomic mass ratio.

Complete answer:
Now in order to calculate the atomicity we will divide the molecular mass of the atom by the atomic mass in each case.
(i) Sulphur:
The atomicity is calculated as:
 $ \Rightarrow \dfrac{{Molecular \, mass}}{{Atomic \, mass}} $
Now we know that for Sulphur
Molecular mass $ = 256 $
Atomic mass $ = 32 $
Substituting these values we get,
 $ \Rightarrow \dfrac{{256}}{{32}} \\
= 8 \\ $
(ii) Phosphorus:
The atomicity is calculated as:
 $ \Rightarrow \dfrac{{Molecular \, mass}}{{Atomic \, mass}} $
Now we know that for phosphorus,
Molecular mass $ = 120 $
Atomic mass $ = 30 $
Substituting these values we get,
 $ \Rightarrow \dfrac{{120}}{{30}} \\
  = 4 $.

Note:
Atomicity of Phosphorus is half times that of Sulphur. We should also note that though valence and atomicity are similar terms but they are different. The total number of atoms in a single molecule of an element is referred to as atomicity. Whereas, The number of electrons in an element's outermost shell is referred to as valency.