Question: What is the smallest atoms called?

Oli Wilson answered on 24 Jun 2020:

Emma’s right, you can use a periodic table (like this one: https://www.ptable.com/) to work out the largest and smallest atoms. An atom’s mass is its number of protons + its number of neutrons (they weigh about the same; electrons don’t really weigh anything). To find an atom’s average mass on a periodic table, look at a square’s larger/higher number. The square’s smaller/lower number tells you how many protons are in an atom, which is the same as its number of electrons (they balance out in uncharged atoms).
So, yes, the smallest atom is Hydrogen (one proton only, mass=1), but the biggest is even heavier than Francium! It’s called Oganesson, with 118 protons and 176 neutrons for a mass of 294! (Like Francium it has 7 electron shells, only its outermost shell has 8 electrons in total rather than Francium’s 1.) It’s man-made, was discovered in 2002 and named in 2016, and only five or six atoms of it have ever been detected!
Also, a final fact, some atoms aren’t on the periodic table – heavy or light versions of standard atoms, called isotopes, are quite common and frequently radioactive. The smallest examples are deuterium (1 proton, 1 neutron, mass=2) and tritium (1 proton, 2 neutrons, mass=3) – they’re both isotopes of hydrogen because they still have one proton, and they’re both smaller than the next atom on the periodic table (helium – 2 protons, 2 neutrons, mass=4). No atom or isotope is smaller than hydrogen, though – with only one proton in it, its nucleus has nothing to lose!