A potassium atom has atomic number 19 and a mass number of 39 - Junior Cycle Science - Question d - 2010

In the potassium atom, the arrangement of electrons can be represented as follows:

• The first shell (or orbit) holds 2 electrons.
• The second shell holds 8 electrons.
• The third shell holds 8 electrons.
• The fourth shell holds 1 electron.

Thus, to illustrate the electron configuration:

• First shell: • •
• Second shell: • • • • • • • •
• Third shell: • • • • • • • •
• Fourth shell: •

The complete diagram should show 2 electrons in the first orbit, 8 electrons in the second orbit, 8 electrons in the third orbit, and 1 electron in the fourth orbit, represented clearly by dots or crosses.