What are atoms made of?

Image created using Canva by me
Atom image from openclipart.org

The atom is the most quintessential symbol in science.  It is commonly drawn as a circle with smaller circles orbiting it. What do those circles represent? And what are those circles made of?

Atoms may make up the world around us, but let's be curious and ask, 'what are atoms made of?'

Atomic constituents

Atoms consist of 3 main constituents: protons, neutrons, and electrons. Protons and neutrons exist in the atom's nucleus (the middle of the atom) packed together. The electrons exist in orbitals around the nucleus.

The diagram to the left shows an atom with 6 protons, 6 neutrons, and 6 electrons. The number of protons tells us its atomic number, which allows us to look it up on the periodic table. This is an atom of carbon.

The protons are positive, so for the atom to be neutral overall we need 6 negative electrons to balance the charge out. If we had more (or less) electrons, then it would still be carbon, but an ion.

The neutrons are neutral (hence their name), and when added to the number of protons, gives us the atomic mass (12 in carbon's case). If it had more or less neutrons it would still be carbon, but an isotope.

The number of protons determines what element it is. Eight protons would be oxygen, 84 protons would be polonium. Every element can have several isotopes, determined by the number of neutrons. Some isotopes are more stable than others.

The reactivity of an element is generally determined by the number of electrons in its outer shell or orbital. In the diagram of carbon, we can see that there are 4 electrons in the outermost shell. That shell can hold up to 8 electrons. Four is a good number and is the reason for carbon being so essential for life. Carbon can form strong bonds with carbon and other elements. Sodium, on the other hand only has 1 electron in its outer shell, and desperately wants to get rid of it and so is highly reactive.

What are protons, neutrons, and electrons made of?

So, we now know what atoms are made of. But what are those bits made of?

"Standard Model of Elementary Particles" by MissMJ -
Own work by uploader, PBS NOVA [1],
Fermilab, Office of Science, United States Department of Energy,
Particle Data Group. Licensed under CC BY 3.0 via Wikimedia Commons.

Well, electrons are fundamental particles (also called elementary particles) in the standard model. This means, as far as we know, they are not made up of any other particles. An electron simply is an electron. Electrons are in a class of particles called leptons (meaning light).

Protons and neutrons are hadrons (meaning heavy). This means they are made up of 3 elementary particles known as quarks. There are six types of quark: up, down, top, bottom, strange, and charm. For our purposes we only need consider up and down quarks.

An up quark has a charge of +2/3, and a down quark has a charge of -1/3. Remembering that protons have a charge of +1, and neutrons 0, we can work out what combination of these quarks are needed. A proton consists of 2 up quarks and a down quark (uud), whereas a neutron consists of an up quark and 2 down quarks (udd).

Curious Fact!

Atoms are actually 99.99999% empty space (because everything is so small, and the spaces between them relatively large). The reason we don't fall through everything is because we are levitating by the electrostatic repulsion between the electrons!

So, now you know what atoms are made of. Please like, +1, comment, share, and tweet this post if you enjoyed. You can share this post with the buttons to the left, and follow It Is All Science using the buttons to the right.