Everything around you, from the air you breathe to the screen you're reading this on, is made of tiny particles called atoms. An atom is the smallest unit of an element that still has all the chemical properties of that element. Think of it like a single Lego brick. You can use that brick to build anything, but it's still fundamentally a Lego.

Atoms themselves are made of even smaller, or subatomic, particles. The three main ones you need to know are protons, neutrons, and electrons.

At the center of every atom is a dense core called the nucleus. This is where you'll find the protons and neutrons packed tightly together. Whizzing around the nucleus in a large area of space is a cloud of electrons.

Each of these particles has a distinct electrical charge. Protons have a positive (+) charge, electrons have a negative (-) charge, and neutrons, as their name suggests, are neutral, with no charge at all.

In a neutral atom, the number of protons is always equal to the number of electrons. The positive and negative charges cancel each other out, giving the atom an overall charge of zero. Protons and neutrons also have a similar mass, while electrons are incredibly tiny, almost 2,000 times less massive.

So, what makes an atom of gold different from an atom of oxygen? It all comes down to the number of protons.

The number of protons in an atom's nucleus is its atomic number. This number is unique to each element and defines what it is. Every single atom with 6 protons is a carbon atom. Every atom with 8 protons is an oxygen atom. No exceptions.

While the protons define the element, the mass of an atom is determined by the total number of protons and neutrons in the nucleus. This is called the mass number. Since electrons have very little mass, they aren't included in this calculation.

The number of protons for an element is fixed, but the number of neutrons can vary. Atoms of the same element that have different numbers of neutrons are called isotopes.

Because they have the same number of protons and electrons, isotopes of an element have the same chemical properties. However, since they have different numbers of neutrons, they have different mass numbers.

A famous example is carbon. Most carbon on Earth is Carbon-12 (6 protons, 6 neutrons). But a tiny amount is Carbon-14 (6 protons, 8 neutrons), a radioactive isotope that scientists use for carbon dating to determine the age of ancient artifacts.

Isotopes have important uses in medicine, energy, and scientific research. They show that even a small change inside an atom's core can give it unique and useful properties.

Time to test your knowledge on the fundamentals of atomic structure.

Understanding these basic components is the first step to exploring how atoms interact to form the molecules and compounds that make up the world.