The given statement is incorrect—atomic radius increases as we down a group. Across a period, valence electrons are added as we move from left to right. This increases the net charge difference in an atom, and as a result, the electrons are pulled more tightly, leading to the shrinking of radius as we move across the period.
Atomic radius trend in the periodic table
- The atomic radius of atoms generally decreases from left to right across a period.
- There are some small exceptions, such as the oxygen radius being slightly greater than the nitrogen radius.
- The atomic radius of atoms generally increases from top to bottom within a group.
- As the atomic number increases down a group, there is an increase in the positive nuclear charge.
- The greater number of principal energy levels outweighs the increase in nuclear charge, and so atomic radius increases down a group.