Question

Discuss the general trend in the following property of the 3d transition elements (21-29):

Atomic size

Answer 1

1. Atomic size generally decreases across the 3d series from Sc (21) to Zn (30) due to increasing nuclear charge pulling electrons closer.
2. The decrease in size is more in the beginning, but becomes less after the middle of the series because added electrons enter the 3d-subshell and shield the outer electrons.
3. From Mn (25) to Ni (28), atomic size remains nearly constant due to the balancing of electron-electron repulsions and nuclear attraction.
4. At the end of the series (Cu, Zn), atomic size slightly increases because electron pairing causes repulsions that expand the electron cloud.
5. Moving down a group, atomic size increases due to the addition of electron shells (not applicable within the 3d series).