Lesson 1Beginner~6 min
What Is an Atom?
Meet the building block of matter: a dense nucleus of protons and neutrons, surrounded by electrons in energy levels.
basicsstructureparticles
Step 1 of 7
Concept
The building blocks of matter
Everything you can touch — air, water, rock, your own body — is made of atoms. An atom is the smallest unit of an element that still behaves like that element.
Atoms are astonishingly small: a single drop of water contains more atoms than there are stars in the observable universe.