How to calculate protons neutrons and electrons worksheet

The number of electrons in an atom is equal to the atomic number of an element, for neutrally charged species. This means the number of electrons and the number of protons in an element are equal. Therefore, the number of electrons in oxygen is 8.

For all atoms with no charge, the number of electrons is equal to the number of protons. The mass number, 40, is the sum of the protons and the neutrons. To find the number of neutrons, subtract the number of protons from the mass number. number of neutrons=40−19=21.