Explain how the period in which an element is located relates to the number of shells that contain electrons.

The period of an element in the periodic table corresponds to the number of electron shells or energy levels that an atom of that element has.

Here's how it works:

1. The periodic table is arranged in rows and columns. The rows are called periods and the columns are called groups.

2. Each period in the periodic table corresponds to a principal energy level (also known as an electron shell) in an atom.

3. The first period has one energy level that can hold up to 2 electrons.

4. The second period has two energy levels. The first level can hold up to 2 electrons and the second can hold up to 8 electrons.

5. The third period has three energy levels. The first level can hold up to 2 electrons, the second can hold up to 8, and the third can hold up to 8 as well.

6. This pattern continues with each subsequent period corresponding to an additional energy level in the atom.

So, by looking at what period an element is in, you can determine the number of electron shells that element has. For example, any element in the third period of the periodic table will have three electron shells.