Question

of the following elements, which one has the smallest first ionization energy?
silicon
boron
carbon
aluminum

Explanation:

Ionization energy generally increases across a period (from left to right) and decreases down a group. Silicon (\(Si\)), boron (\(B\)), carbon (\(C\)), and aluminum (\(Al\)):

• \(Al\) is in period 3, group 13.
• \(B\) is in period 2, group 13.
• \(C\) is in period 2, group 14.
• \(Si\) is in period 3, group 14.

Since \(Al\) is further to the left (compared to \(Si\) in the same period) and lower (compared to \(B\) in the same group) among these elements, it has the least effective nuclear charge pulling on its out - ermost electrons, so it requires the least energy to remove the first electron.

Answer:

aluminum