atoms

Look at all the things around you—your computer, your finger, your desk, even the trees outside. They're all made of atoms. They're so tiny, it would take billions of them just to dot the "i" in the word "atomic"! Atoms are made of even smaller parts: a central nucleus made of protons and neutrons, and electrons that circle around the atom in special patterns called orbitals.

What they are: the building blocks of matter
Number: at least 112 known types; 92 occur in nature
What they're made of: protons, neutrons, and electrons
Mass: protons and neutrons have the same mass; electrons have about 2,000 times less mass than protons and neutrons

Image credits: main image: Eric Hamilton.