the model below shows a calcium atom. how many electrons are in the third energy level? 2 8 18 20

Explanation:

Step1: Recall calcium's atomic number

Calcium (Ca) has an atomic number of 20. This means it has 20 electrons.

Step2: Know electron - shell filling rules

The first energy level can hold a maximum of 2 electrons. The second energy level can hold a maximum of 8 electrons.

Step3: Calculate electrons in the third level

After filling the first two levels (2 + 8 = 10 electrons used), the remaining electrons go to the third level. 20 - 10 = 10, but the third level fills up to 8 electrons before electrons start filling the fourth level for calcium. So, there are 8 electrons in the third energy level of a calcium atom.

Answer:

8