Question

Look at the atomic radii of some elements of second period and answer the questions:

Element	B	Be	O	N	Li	C
Atomic radii in pm	88	111	66	74	152	77

Arrange these elements in the decreasing order of their atomic radii.

Answer 1

Step-1: Introduction

Atomic radii is the distance of the electrons in the outermost shell from the atomic nucleus. It increases from top to bottom in a group and decreases from left to right in a period but is highest for a noble gas.

Step-2: Arrangement of period 2 elements

The elements of period 2 are arranged in wrong order. The correct order of elements is given below:

Element	Li	Be	B	C	N	O
Atomic radii in pm	152	111	88	77	74	66

Step-3: Atomic radii of period 2 elements

The elements given are period 2. The correct order of period 2 elements are Lithium ($\mathrm{Li}$), Beryllium ($\mathrm{Be}$), Boron ($\mathrm{B}$), Carbon ($\mathrm{C}$), Nitrogen ($\mathrm{N}$) and Oxygen ($\mathrm{O}$) with atomic number 3, 4, 5, 6, 7 and 8 respectively.

Across the period, atomic size drops as move on from left to right. The reason is due to rise in proton number and it results in higher electrons attraction. The elements in extreme left have larger atomic size.

The decreasing order of atomic radii is Lithium, Beryllium, Boron, Carbon, Nitrogen and Oxygen.

Final answer

Therefore, the atomic radii of period 2 elements in decreasing order is Lithium, Beryllium, Boron, Carbon, Nitrogen and Oxygen.