Question

In the modern periodic table, how does the atomic size of the elements vary along the period and down the group? Explain.

Answer 1

Hint: Before talking about the answer, you should know what is atomic size. It is the distance from the center of the nucleus to the boundary of the surrounding shell. As we move across the periods, more number of electrons are added in the same shell. And as we move down the group, the extra shells of electrons are added.

Complete step by step answer:
In the modern periodic table, as we go from left to right in a period, more electrons are added in the same shell. Because of this, the attraction between the electrons and nucleus is increased which makes the size of the atom smaller. So, as we move from left to right along the period, the size of the atom starts decreasing.
And as we move down the group, that means, from top to bottom, the atomic number increases because extra shells of electrons are added into the atom, due to which the atomic size increases. So, as we move from top to bottom down the group, the size of the atom increases.

Additional information:
1. Atomic size is defined as the radius of an atom, which means, the distance from the center of the nucleus to the boundary of the surrounding shell.
2. Atomic size can be estimated, when two identical atoms are combined together, one can check the distance between the nuclei of the two identical atoms.
3. Atomic radius of an atom is measured by spectroscopy.
4. As we move across the periodic table, there is an increase in nuclear charge, that overcomes the repulsion between the additional electrons in the valence line. Hence, the size of atoms decreases as we move across the period.

Note: As we move across the period, the size of the atom decreases because effective nuclear charge increases and electron shielding remains constant. As we move down the group, the size of the atom increases because the number of shells increases.