Choose the element with the more negative (more exothermic) electron affinity from each pair.
a. Mg or S
b. K or Cs
c. Si or P
d. Ga or Br.
Answer:
- A: S
- B: K
- C: Si
- D: Br
Explanation
PART A:
Magnesium and sulfur are both located in the same row in the periodic table. As a general rule, electron affinities for main group elements become more negative moving right across a period. Sulfur is located to the right of magnesium. Therefore, sulfur is expected to have a more negative electron affinity.
PART B:
Potassium and cesium are both located in Group 1A in the periodic table. As a general rule, electron affinity for alkali metals becomes less negative moving down the column. Cesium is located below potassium. Therefore, potassium is expected to have a more negative electron affinity.
PART C:
Silicon and phosphorus are both located in the same row in the periodic table. Normally you would expect that phosphorus would have a more negative electron affinity. However, phosphorus has a half-filled subshell, which lends it extra stability. Thus, it is harder to add an electron and silicon, therefore, has a more negative electron affinity.
PART D:
Gallium and bromine are both located in the same row in the periodic table. As a general rule, electron affinities for main group elements become more negative moving right across a period. Bromine is located to the right of the gallium. Therefore, bromine is expected to have a more negative electron affinity.
