How to Find the Number of Protons, Neutrons, and Electrons?

To determine the number of protons, neutrons, and electrons in an atom, follow these straightforward steps:

1. Number of Protons

The number of protons in an atom is equal to its atomic number.

You can find the atomic number on the periodic table above the element’s symbol. For example, oxygen has an atomic number of 8, so it has 8 protons.

2. Number of Electrons

For a neutral atom (uncharged), the number of electrons equals the atomic number—because positive protons and negative electrons balance out. So, oxygen has 8 electrons as well.

If the atom has a charge (ion), the number of electrons is atomic number minus the charge. For example, an aluminum ion with a +3 charge (Al³⁺) has 13 protons and 10 electrons (13 − 3 = 10).

3. Number of Neutrons

The number of neutrons is calculated by subtracting the atomic number from the mass number. The mass number is typically found below the element’s symbol on the periodic table (but is sometimes rounded from the atomic mass). For oxygen, with an atomic number of 8 and a mass number of 16, the number of neutrons is 16 − 8 = 8.

Note: Isotopes (forms of the same element with different neutron numbers) can have different masses, so the mass number for a specific isotope is usually given.

Example Calculation

Let’s calculate for bromine-80 (80₃₅Br):

• Atomic number (Z): 35 ⇒ Protons: 35
• Electrons: 35 (assuming no charge)
• Mass number (A): 80 ⇒ Neutrons: 80 − 35 = 45