Choose the element with the larger atoms from each pair.
(a) Sn or Si
(b) Br or Ga
(c) Sn or Bi
(d) Se or Sn
Atomic radii get smaller as you move right and up in the periodic table (opposite of the ionization energy trend)
(a) Sn or Si: Sn has the larger radius; its outermost electrons are in the 5p orbital as opposed to the 3p orbital (in Si)
(b) Br or Ga: Ga has the larger radius; the core charge in Br is higher, so the outermost shell is pulled in more tightly toward the nucleus