Atom Calculator

All atoms are made up of three types of particles and this calculator allows you to work out the number of each. Enter the atomic number and mass number for an element and if working with ions also enter the charge to show the number of protons, neutrons and electrons. It is also possible to work backwards from the particle numbers: enter the number of any of the particles and it will display the atomic number, mass number and charge so you can identify the element and whether or not it is an ion.

What are atoms made of?

Atoms are made up of a small, dense nucleus surrounded by an electron cloud. The nucleus contains protons, which have a positive charge, and neutrons, which have no electrical charge. Electrons carry a negative charge and orbit the nucleus. In a neutral atom, there are exactly as many electrons as there are protons, so that the entire atom has no net charge.

Three numbers and three simple relationships connect everything together. The atomic number Z is the number of protons. The mass number A is the sum of the number of protons and neutrons, since protons and neutrons are heavy particles in the nucleus of an atom. The charge is the difference between the number of protons and the number of electrons.

Formula.

If you start with the atomic number, mass number and charge, then you can determine the number of three particles simultaneously.

Let's take a closer look at the last equation. Since a neutral atom has no charge, the number of electrons is equal to the number of protons. If you remove an electron, then the charge becomes positive one, so the number of electrons in a cation is less than the number of protons. If you add an electron, then the charge becomes negative one.

You can also use this relationship in reverse. If you know the number of particles, you can get information about the element.

Example calculation: Sodium

The atomic number of a sodium atom is 11, the mass number is 23 and the charge on the atom is zero. These values are substituted into the first three equations.

Thus a neutral sodium atom contains 11 protons, 12 neutrons and 11 electrons. This is the result that will be shown by default when you open a calculation tool.

Example of a back calculation: sulfide ion

So here we are assuming that you have measured 16 protons, 16 neutrons and 18 electrons. So if you switch to the second mode, then you can use an inverse formula.

The atomic number of 16 corresponds to sulfur and the extra two electrons give it a charge of -2. This identifies it as a sulfide ion which is abbreviated with an S with a -2 superscript on the top right.

Ions: cations and anions

The position of the protons does not change but the number of electrons can vary. This is what causes ions to form. When one or more electrons are removed from an atom, there are more protons than electrons in that atom which results in a positive ion. This is called a cation. Conversely, adding electrons to an atom will result in a negative ion. This is known as an anion. The charge shown by the calculator is the difference between the number of protons and the number of electrons with the sign (+ or -) indicating what type of ion it is.

Isotopes and Atomic Masses

Two atoms of the same element always have the same number of protons but can differ in the number of neutrons. These variants are called isotopes, and the only difference is their mass number. Carbon with 6 neutrons is called carbon-12, while carbon with 7 neutrons is called carbon-13. However, both are still carbon.

To find the mass of an atom, simply add up the number of protons and neutrons. The mass of electrons is very small, about one two-thousandth the mass of a proton, so it makes little difference to the total mass. This sum, expressed in atomic mass units, is why it comes close to being the relative atomic weight on the periodic table.

The number of protons is an element's fingerprint.

There are no two elements with the same number of protons. The element with one proton is hydrogen, the element with six protons is carbon, and the element with eleven protons is sodium. This continues all the way to the top of the periodic table. Changing the number of neutrons produces isotopes, while changing the number of electrons produces ions. However, if you change the number of protons, then you have a completely different element.

Number of particles for first twelve elements:

Since each row uses the most common isotope, the number of neutrons can be found by subtracting the atomic number from the mass number.

Here's how to use this calculator.

At the top select a mode. In the first mode enter the atomic number and mass number and set the charge. Use zero for neutral atoms. The numbers of protons, neutrons and electrons are immediately shown. In the second mode enter the numbers of the three particles and read off the atomic number, mass number and charge.

The right panel also shows the approximate atomic mass and tells you whether the result is a neutral atom or an ion. When you open the graph, you'll see a bar chart with the number of each of the three particles as well as a nucleus made up of protons and neutrons.

This tool simulates a single atom or monatomic ion, which is made up of an integer number of particles. The atomic mass shown is the mass number itself and is only approximate. The atomic weights on the periodic table are average values for the naturally occurring isotopes of that element.