Chemistry · Atoms
Build an Atom
An atom is made of protons and neutrons in the nucleus, with electrons in shells around it.
- Element
- Carbon (C)
- Atomic number Z
- 6
- Mass number A = p + n
- 12
- Charge
- 0 (neutral atom)
- Electron shells (K, L, M, N)
- 2, 4
- Valence electrons
- 4
Protons
6
Neutrons
6
Electrons
6
Try this
- Build a neutral carbon atom.
- Make a sodium ion (Na⁺). How many electrons does it have?
- Which atoms have a full outer shell?
Key ideas
- Atomic number (Z) = number of protons.
- Mass number (A) = protons + neutrons.
- Shells fill as K = 2, L = 8, M = 8 (for the first 20 elements).