Question

Arrange the following elements in increasing order of their atomic radii.
Cl, At, Br, I
(A). Cl(B). Cl(C). Cl(D). Br

Answer 1

There are two major factors that contribute towards the effect in the atomic radius of an atom. They are the number of shells in an atom and the effective nuclear charge on an atom. They decide the trend in the atomic radii both across the period and down the group.

Complete step by step solution:
-The periodic table is made in such a form that it can show the variations of several properties of the atoms both along the period and down the group. So, there is also a trend for the atomic radius both across the period and down the group.
-There are 7 periods and 18 groups in periodic tables where atoms are arranged in the increasing order of their atomic number because the atomic number gives us the number of electrons of the atom. Electrons only decide the chemical properties of an atom as they are loosely held by the atom.
-Atomic radius of an atom denotes the shortest distance between the centre of the nucleus of an atom to the last shell of electrons of that atom. This is why atomic radius is different for a neutral atom, its anion formed when an electron is added to the atom and its cation formed when electrons are taken away from the atom.
-Along the period, the atomic number increases and so does the number of electrons without altering the number of shells of atoms. So effective nuclear charge increases thereby increasing the force of attraction of the nucleus towards the electrons. This leads to decrease in the atomic radii across a period.
-Down the group, the number of shells increases but the valence electrons remain the same. Atomic size increases down the group. This increases the distance between the nucleus of an atom to the valence electrons. So the atomic radii increase down the group due to the number of shells.
-In the question, we can see that all the elements belong to group 17 of the periodic table. So they are of the same group. We know that the atomic radius increases down the group. So the order of the atomic radii will be Cl
Therefore the correct option is (A).

Note: Atomic distance is different from molecular distance. Molecular distance is the distance between the centres of two atoms of the molecules while the atomic radius is the distance of the centre of an atom to its last electron shell.