CNC Illustration by Gwendolyn Say (@saydrawings)

1. We identify an element by the number of protons

The term proton comes from the Greek word protos, which means first. Indeed, the proton was the first heavy subatomic particle to be discovered, just 20 years after the discovery of the electron that is around 2000 times lighter. It is also the first thing we consider when we identify an element.

Even though the three particles have different number of neutron and electron, they are all hydrogen as they have 1 proton

Every element has a unique number of protons. This is pretty neat as it allows us to identify an atom or an ion by counting the number of protons it has. For example, even though the three particles shown above have very different number of neutrons and electrons, they are all hydrogen as they have 1 proton.

Since the proton number identifies an atom, it is also called the atomic number.

All atoms and ions of the same element have the same proton number (atomic number).

2. The Periodic Table: our cheat sheet to find the proton number

In the Periodic Table, the proton number (highlighted) is given as the smaller number above the chemical symbol

The Periodic Table tells us the proton number, which is the smaller number on top of the chemical symbol. It also neatly arranges the elements by increasing proton number. This means that as we read the table from the top row, going from left to right, the proton number increases one by one.

For example, the proton number increases from 1 to 2, as we move right from hydrogen to helium. After helium comes lithium in the next row, which has a proton number of 3.

3. Protons are squeezing in the nucleus

Even though iron-56 has 26 protons, they are all held very tightly together in the nucleus by the strong force

A proton has a relative charge of 1+. Since like charges repel, early scientists expected protons to be spread out in an atom.

Yet, the earnest work of Ernest Rutherford and his colleagues in the 1900s blew everyone’s mind. They realised that the protons of an atom are squeezed within the narrow confines of the nucleus. The packing is way more intense than how students are squeezed into the school hall for assemblies. Perhaps imagine squeezing the entire school into a classroom?

This suggests that is another extraordinary force holding the protons together, stronger than the electrostatic repulsion. Lo and behold, this stronger force is called the strong force, which is mediated by the neutrons. This explains why any element with 2 or more protons necessarily has neutrons in their nucleus.

All the protons of an atom are concentrated in the nucleus.

4. Protons are the invisible hand behind a chemical reaction

If protons are hidden in the nucleus and bound tightly by the strong force, how do they influence a chemical reaction and hence shape the chemical identity of an atom?

Indeed, protons remain unchanged in a chemical reaction. It is the electrons that get passed around or shared between atoms.

However, we can see the protons of an atom as the puppeteer pulling the strings behind the scene. The number of protons influences the positive charge of the nucleus, causing it to attract an equal number of negatively charged electrons. If the attraction is felt strongly by the electrons, the nucleus can pull even more electrons in. On the contrary, weak attraction causes the nucleus to let go of its outermost electrons.

Proton number determines the number of electrons in an atom, which influences the number of electrons that can be gained or lost during a chemical reaction.

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