Question

of the following elements, which one has the smallest first ionization energy?

aluminum
silicon
carbon
boron

Explanation:

Ionization energy is the energy required to remove an electron from an atom. In the periodic table, ionization energy generally increases across a period (from left to right) and decreases down a group. Aluminum (Al), silicon (Si), carbon (C), and boron (B) - among these, aluminum is in period 3 and group 13. Boron is in period 2 group 13, carbon in period 2 group 14, silicon in period 3 group 14. Since aluminum is further to the left (compared to Si in the same period) and lower (compared to B and C in higher periods), it has the least effective nuclear charge attracting its outer - shell electrons among these four, so it requires the least energy to remove the first electron.

Answer:

aluminum