Question

1. an atom with electron arrangement 2–8–7 will most likely: *

• become bigger when it gains electron
• become bigger when it loses electron
• become smaller when it gains electron
• remain the same size when it gains electron

Explanation:

1. First, analyze the electron arrangement \(2 - 8 - 7\). The atom has 17 electrons (since \(2+8 + 7=17\)), so it is chlorine (Cl). Chlorine is a non - metal and has a tendency to gain an electron to achieve a stable octet configuration (\(2 - 8 - 8\)).
2. When an atom gains an electron, the number of electrons increases. The electron - electron repulsions in the outermost shell increase, and the effective nuclear charge on the valence electrons decreases relatively. This causes the electron cloud to expand, and the atomic radius (size of the atom) increases.
3. When an atom loses an electron, the number of electrons decreases. The effective nuclear charge on the remaining electrons increases, pulling the electrons closer to the nucleus, and the atomic radius decreases. So, for a chlorine atom (with electron arrangement \(2 - 8 - 7\)), when it gains an electron, it becomes bigger.

Answer:

A. Become bigger when it gains electron