Atom Calculator

Created by Anna Pawlik, PhD candidate
Reviewed by Bogna Szyk and Adena Benn
Last updated: Jul 16, 2022

The atom calculator is a tool for calculating the atomic number and the mass number based on the number of atom components - protons, neutrons, and electrons (or vice versa). In addition, you can define the charge of ions with known numbers of protons and electrons. This article will provide you with:

  • Definitions of:
    • Atom;
    • Atom components;
    • Atomic number; and
    • Mass number.
  • The equations used to calculate the number of:
    • Protons;
    • Neutrons;
    • Electrons;
    • Atomic number;
    • Atomic mass and
    • Atomic charge.
  • Lastly, A short step-by-step tutorial on how to calculate:
    • Atomic number;
    • Atomic mass; and
    • Charge.

What is an atom?

🙋 An atom is the smallest constituent unit of matter that retains the properties of an element.

A typical atom consists of a nucleus and electron cloud. Atom components are positively-charged protons and electrically neutral neutrons in the nucleus with negatively-charged electrons orbiting this nucleus. Protons and neutrons are called nucleons.

Atoms are electrically neutral because they possess an equal number of electrons and protons. However, when an atom has an unequal number of protons and electrons, it has an electrical charge and creates ions.

🙋 If an ion has more protons than electrons, it is positively charged and is called a cation. Conversely, if an ion has more electrons than protons, it is negatively charged and is called an anion.

Some atoms can split into smaller parts (lighter nuclei). You can use our Half Life Calculator to calculate the number of nuclei remaining after a particular time.

Atomic number, atomic mass

Atom is uniquely identified with the atomic symbol Z. The atomic number is the number of protons present in the nucleus. In the case of uncharged atoms, the atomic number is equal to the number of electrons.

In contrast, in ions, the number of electrons is the difference between the atomic number and the charge of ions.

In cations, there are fewer electrons than protons, while in anions, there are more electrons than protons.

The number of neutrons in a given element, however, can vary. The variants of the same chemical element with a different number of neutrons are called isotopes. Protons and neutrons determine the mass of an atom. Mass number symbol A is the sum of the number of protons and neutrons.

It is vital to know the number of atoms that make up a molecule, as it serves as the base for many estimations such as degree of unsaturation. It provides information about the structure of a molecule.

Equations used to calculate the numbers of protons, neutrons, electrons, atomic mass, and atomic charge

  • If you know the atomic number (Z), atomic mass (A), and charge (z), you can calculate the numbers of protons (p), neutrons (n), and electrons (e) using the given mathematical equations 1-3:

    1. p = Z

    2. n = A - Z

    3. e = Z - z

  • On the other hand, if you know the number of protons (p), neutrons (n), and electrons (e), you can calculate the atomic number (Z), atomic mass (A), and charge (z) using equations 4-6:

    1. Z = p

    2. A = p + n

    3. z = p - e

How to calculate the atomic number, mass and charge

  1. Choose your element. Let's assume that it is the atom of sodium (Na). The charge is 0.

  2. Find the atomic number (Z) and mass number (A). They are equal to 11 and 23, respectively.

  3. Calculate numbers of protons, neutrons, and electrons by using mathematical expressions (1-3):
    p = 11 (1)

    n = 23 - 11 = 12 (2)

    e = 11 - 0 = 11 (3)

  4. Alternatively, you can also calculate the atomic number, atomic mass, and charge.

  5. Choose your element. Let's assume that it is the sulfide anion.

  6. Find the numbers of protons, neutrons, and electrons. They are equal to 16, 16 and 18, respectively.

  7. Calculate atomic number, atomic mass, and charge by using mathematical expressions (4-6):

    Z = 16 (4)

    A = 16 + 16 = 32 (5)

    z = 16 - 18 = -2 (6)

Of course, you don't have to perform all these calculations by hand! Type any three values into this atom calculator and watch it do all the work for you.

Did you find this calculator helpful? We also have a mass percent calculator that may interest you.

Anna Pawlik, PhD candidate
Atomic number
Mass number
Atomic composition
Number of protons
Number of neutrons
Number of electrons
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