What Are Atoms?
helium atom
A Helium Atom
Atoms are the building blocks of visible matter in the Universe. The word atom is derived from the ancient Greek word ‘atomos’ meaning indivisible or uncuttable. Ancient philosophers contemplated that if you kept cutting an object, breaking it down into its smallest constituents, you would eventually reach a piece that would be so small it would be impossible to cut it any further. Even now we know that you can in fact ‘cut’ an atom science has kept the word as it pretty much describes what they are.
Atoms are mysterious objects and we still have much to learn about them. They are abstract in their structure but science has done its best to describe them in ways we can understand.
At the center of an atom is the nucleus which is made up of protons (p+) and neutrons (n). Protons have a positive electrical charge whereas neutrons don’t have any electrical charge.

The number of protons determines what element the atom is, so an atom with 1 proton is hydrogen, 2 protons is helium, 3 protons is lithium and so on. The number of protons also gives the element its atomic number, so the atomic number of helium is 2, you will see this number written above each element in a periodic table. The number of neutrons that any single element may have can vary which will result in a different version of that same element, called an isotope.

Moving around the nucleus of the atom are the electrons (e-) which have a negative electrical charge, attracting them to the positively charged protons. The number of electrons equals the number of protons in any single atom, so a helium atom for example will have 2 electrons. If an atom has more or less electrons than protons it becomes an ion, which is an electrically charged atom.

In some depictions or drawings of atoms it seems like the electron is orbiting around the nucleus in a predicted path, rather like the way a planet goes around the sun. This is in fact not correct, an electron could be anywhere around the nucleus at any one time.

Atoms interact with each other, joining to form into molecules. So if two hydrogen atoms join they become a hydrogen molecule. If different types of atom join the molecule will also become a compound, for example if two hydrogen atoms join one oxygen atom it becomes the chemical compound H2O, otherwise known as water. The Universe is in essence one giant chemical factory with atomic interactions creating stars, galaxies, nebulae, planets, and importantly for us even life itself.

To give an idea of how small an atom is a grain of sand contains billions upon billions of atoms. Each atom has a miniscule amount of mass calculated by how many protons and neutrons they have, but this is only a tiny percentage of its entire volume, 99.999% of an atom is empty space. The visible Universe, the observable world that we inhabit is in fact mostly nothing.