Why is Copper smaller than zinc?

Generally the atomic radius of d-block elements in series is decrease with increase in atomic number. * But the radius of transition elements is decreased `Scandium` to `Chromium` after that it remains stable and increases in last. read more

In transition elements `Scandium` to `Chromium`, nuclear charge is higher than shielding (screening) effect. Therefore, atomic radius decreases. In IRON , COBALT and NICKEL, nuclear charge is almost same as their screening effect. Therefore, atomic radius is same. In COPPER and ZINC nuclear charge is lower than screening effects. read more