Question

Explain variation of atomic size in the periodic table.

Answer 1

Answer:

Atomic radii vary in a predictable and explicable manner across the periodic table. ... The atomic radii decrease across the Periodic Table because as the atomic number increases, the number of protons increases across the period, but the extra electrons are only added to the same quantum shell.

Answer 2

$\large{ \bf{ \underline{Periodic \: Trend \: in \: Atomic \: Size}}}$

• Atomic Size generally decreases across the period whereas there is an increase in the size down the group.
• Reason attributed to this variation is the nuclear charge.
• In a period as the atomic number increases, the increasing number of electrons are added to the same valence shell. This increases the effective nuclear charge, consequently the force of attraction of the electrons to the nucleus goes on increasing. The gradual increase in the effective nuclear charge results in the decrease of the atomic size.
• Down the group or in the vertical column of the periodic table there is a regular increase in the atomic radii with the increase in atomic number. As we know, in a group there is an increase in the principal quantum number (n) due to the addition of a new shell. The added new shell increases the distance of the valence electrons from the nucleus, consequently the size of the atom increases.So, even though the atomic number goes on increasing, the size increases because of another factor know as 'shielding effect' comes into play. The lower energy level electrons (inner energy levels) are filled with electrons which serve to shield the outer electrons from the pull of the nucleus, hence, the magnitude of nuclear attraction decreases.