# Calculate the number of protons, electrons and neutrons in an atom

For years it has been known that the atom is composed of an atomic nucleus where almost all its mass is concentrated and then it is surrounded by a cloud of electrons. This was discovered in the twentieth century, since before, it was believed that atoms were indivisible. In fact, the nomadic atom means "without division".

With the investigations it was also discovered that the nucleus also has its parts, these are the protons, with positive charge, and neutrons, electrically neutral. The electrons - which are negatively charged - remain attached to the nucleus by the electromagnetic force.

## How do I calculate the number of protons and electrons in an atom?

Use the table of the elements to find the atomic number and the atomic weight of an element. The atomic number is in the upper left corner, and the position of the atomic weight varies, but is usually in the upper right corner, above the symbol of the element.

## The number of protons

The atomic number is the number of protons in an atom of the element. In our example we will use the chromium (Cr), and its atomic number is 24. This tells us that a chromium atom has 24 protons in its nucleus.

The interesting thing here is that each chromium atom contains 24 protons. If an atom does not have 24 protons, it can not be a chromium atom. Adding or removing protons from the nucleus creates a different element. For example, by removing a proton from a chromium atom, a Vanadium atom (V) is created.

## The number of electrons

By definition, atoms have no electrical charge. This means that there must be a balance between the positively charged protons and the negatively charged electrons. Atoms have the same number of protons and electrons . In our example, a chromium atom must contain 24 electrons since it contains 24 protons.

An atom can gain or lose electrons, becoming what is known as an ion. An ion is nothing more than an electrically charged atom. Adding or removing electrons from an atom does not change the element, only its charge.

## The number of neutrons

To start you need to find the mass number, which is symbolized by the letter A. Unfortunately, the mass number does not appear in the table of the elements. Luckily, to find the mass number, all you have to do is round the atomic weight to the nearest whole number. In our example, the chrome mass number is 52 since its atomic weight is 51, 996.

The mass number is a count of the number of particles in the nucleus of an atom. Remember that the nucleus is made up of protons and neutrons . Therefore, you can write:

Mass number = (number of protons) + (number of neutrons)

The atomic number 24 is the number of protons in the chromium, and its mass number is 52.

52 = 24 + (number of neutrons)

What number added to 24 gives 52? We solve the equation and the result is 28. That is the number of neutrons in a chromium atom.

The interesting thing here is that the addition or elimination of neutrons in an atom does not create a different element. Rather, it creates a heavy or lighter version of that element. These different versions are called isotopes and most of the elements are actually a mixture of different isotopes.

Any questions or queries you have, you can leave them in a comment.