Explain each of the following observations using principles
of atomic structure and/or bonding
c) A calcium atom is larger than a zinc atom.
Ca (1s2)(2s2,2p6)(3s2,3p6)
(3d0) (4s2) Z*
= 20 – (10 · 1.00 + 8 · 0.85 + 1 · 0.35) = 2.85
Zn (1s2)(2s2,2p6)(3s2,3p6)
(3d10) (4s2) Z*
= 30 – (10 · 1.00 + 18 · 0.85 + 1 · 0.35) = 4.35
The electrons in the 4s level experience a
greater effective nuclear charge in Zn than in Ca. The
electrons in Zn are therefore attracted to the nucleus to
a larger extent than the electrons in calcium. So the
atomic radius is smaller. In general the Z*
increases more slowly across a d block compared to
a p block. The reason is the electrons being added
in the dblock are inside the ns electrons,
while for the p block the electrons are not inside
the ns electrons.