Humber Admissions Practice Test

How does ionization energy change as you move across a period from left to right?

1. Increases

2. Decreases

3. Remains the same

4. Fluctuates

The correct answer is: Increases

As you move across a period from left to right on the periodic table, ionization energy typically increases. This is primarily due to the increasing nuclear charge, which occurs as protons are added to the nucleus of the atoms. As the positive charge of the nucleus increases, it exerts a stronger attractive force on the electrons surrounding it. The electrons are held more tightly by this stronger pull, making it more difficult to remove one of them, which is what ionization energy measures. Additionally, the added electrons are being added to the same energy level without significantly increasing the distance from the nucleus, which contributes to the increased attraction. In contrast, as you move down a group, ionization energy decreases because the electrons are located in higher energy levels, further away from the nucleus, and are thus less tightly held. The trend of increasing ionization energy across a period is a fundamental concept in understanding the periodic trends in chemistry.