Name: Variation of Atomic Radius in Periodic Table
Uploaded: 2019-07-19
Duration: 4 min 6 s
Description: The atomic radius is defined as the distance between the atom's nucleus and the outermost shell. But do you know how it varies in the periodic table? Let's find the answer in this video.

Question

Discuss briefly the anomalous behaviour of elements of second period.

Accepted Answer

The first element of each of the Group- $1$ (lithium) and Group- $2$ (beryllium) and Groups $13 - 17$ (boron to fluorine) differs in many respects from the other members of their respective groups. For example, lithium unlike other alkali metals, and beryllium unlike other alkaline earth metals, form compounds which have significant covalent character ; the other members of these groups, predominantly form ionic compounds.

In fact, it has been observed that some elements of the second period show similarities with the elements of the third period placed diagonally to each other, though belonging to different groups. For example, lithium (of Group- $1$ ) resembles magnesium (of Group- $2$ ) and beryllium (of Group- $2$ ) resembles aluminium (of Group- $13$ ). This similarity in properties of elements placed diagonally to each other is called diagonal relationship.

The main reasons for the different chemical behaviours of the first member of a particular group of elements in the $s$ and $p$ -blocks compared to the other members of the same group are presumably its (i) small size, (ii) large charge/radius ratio, (iii) high electronegativity and (iv) absence of $d$ -orbitals.

Discuss briefly the anomalous behaviour of elements of second period.

Important Questions on Classification of Elements and Periodicity in Properties

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