Humber Admissions Practice Test

Which of the following correctly describes ionization energy across a group?

1. It stays the same

2. It increases

3. It decreases

4. It fluctuates

The correct answer is: It decreases

Ionization energy refers to the energy required to remove an electron from an atom in its gaseous state. When considering the trend of ionization energy across a group in the periodic table (from top to bottom), it's important to recognize that as you move down a group, the ionization energy generally decreases. This occurs because, as you progress down a group, additional electron shells are added to the atoms. Each new shell is further away from the nucleus, which causes the outermost electrons to experience greater shielding from the positive charge of protons in the nucleus. This increased distance and shielding effect make it easier to remove an electron, thereby reducing the ionization energy required. As a result, the correct concept is that ionization energy decreases as you move down a group in the periodic table, which makes this understanding crucial for predicting chemical behavior and bonding characteristics of elements.