Hydrogen
H- Atomic number
- 1
- Mass number
- 1
- Protons
- 1
- Neutrons
- 0
- Electrons
- 1
- Configuration
- 1
Electrons per shell
Neutrons = 1 − 1 = 0
Learn the basics
Atomic number (Z)
The number of protons in the nucleus. It defines which element an atom is — every carbon atom has 6 protons.
Mass number (A)
The total number of protons plus neutrons in the nucleus. Different isotopes of an element have different mass numbers.
Protons
Positively charged particles in the nucleus. Protons = atomic number.
Neutrons
Neutral particles in the nucleus that add mass. Neutrons = mass number − atomic number.
Electrons
Tiny negatively charged particles around the nucleus. In a neutral atom, electrons = protons.
Electronic configuration
How electrons are arranged in shells. For the first 20 elements shells fill as 2, 8, 8, 2 — e.g. sodium is 2,8,1.
A note about the Bohr model
The Bohr model is a simplified picture that helps us count electrons and see which shell (energy level) they occupy. In modern quantum mechanics, electrons do not travel in literal circular paths. Instead, they are described by orbitals — regions of probability where an electron is likely to be found. The animation here is a teaching aid, not a literal image of an atom. Sizes are also not to scale: a real nucleus is about 100,000 times smaller than the atom.