The model below shows a calcium atom.

Question

An image has a mix of red and blue balls in its center and 4 concentric black rings around the center. The first ring from the center has 2 small green balls on it. The second ring has 8 small green balls on it. The third ring has 8 small green balls on it. The outermost ring has 2 small green balls on it.

How many electrons are in the third energy level?

2
8
18
20

Answer 1

A calcium atom has a total of 20 electrons. The electron configuration of calcium can be broken down as follows:

• The first energy level (1s) can hold a maximum of 2 electrons.
• The second energy level (2s and 2p) can hold a maximum of 8 electrons.
• The third energy level (3s and 3p) can also hold a maximum of 8 electrons.

From the description you provided, the placement of electrons is as follows:

• 1st ring (first energy level): 2 electrons (2 small green balls)
• 2nd ring (second energy level): 8 electrons (8 small green balls)
• 3rd ring (third energy level): 8 electrons (8 small green balls)
• 4th ring (fourth energy level): 2 electrons (2 small green balls)

Thus, the number of electrons in the third energy level is 8.