Choose The Element With The More Negative (More Exothermic) Electron Affinity From Each Pair:

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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.

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