Question

Arrange the following elements in the increasing order of atomic radii.
(A) F < O < C < Cl < Br
(B) F < C < O < Cl < Br
(C) F < Cl < Br < O < C
(D) C < O < F < Cl < Br

Answer 1

The atomic radius shows the distance between the centre of the atom and the valence orbital of the atom. In a particular period of the periodic table, atomic radius of elements decreases with increase in atomic number.

Complete step by step answer:
Let us first try to understand what the atomic radius of an element really is before moving on to try and understand the trends of atomic sizes in the Periodic Table.
The atomic radius of a chemical element is defined as ‘a measure of the size of its atoms, usually the mean or typical distance from the centre of the nucleus to the boundary of the valence shell of electrons.’

Let’s see how their atomic radii will be related with each other.

Bromine is an element of the fourth period while all the other elements given are of second and third period. So, bromine will have an extra shell of electrons and hence its atomic radius will be biggest amongst all.
Now, chlorine is a third period element and hence it will have a shell of electrons more than the second period elements. So, its atomic radius will be more than second period elements and less than bromine.
C, O and F are elements of the same period and in the same period atomic radius decreases with increase in atomic number. C, O and F have atomic numbers of 6, 8 and 9 respectively. So, fluorine will have the smallest atomic radii among them three and oxygen will have smaller atomic radii than carbon’s.
Atomic radii decrease with increase in atomic number because within the same period the number of shells of electrons do not increase but positive charge on nucleus gradually increases.

Thus, we can conclude that the answer to this question is option (A).

Note: It is possible for a vast majority of elements to form covalent molecules in which two like atoms are held together by a single covalent bond. The covalent radii of these covalent molecules are often regarded as atomic radii.