science

Bohr model

An atomic structure representation where electrons travel in circular orbits around a central nucleus at fixed energy levels.

Proton

A subatomic particle found in the nucleus with a positive electric charge of $+1$ and a relative mass of approximately $1$.

Neutron

A neutral subatomic particle located in the nucleus that carries no electrical charge and has a relative mass of approximately $1$.

Electron

A subatomic particle carrying a negative electric charge of $-1$ that occupies quantized energy shells outside the nucleus.

Valence electrons

The electrons located in the outermost energy level of an atom that govern chemical bonding and reactivity.

Maximum electron capacity of the first three Bohr shells

$2$ electrons in shell 1, $8$ electrons in shell 2, and $8$ electrons in shell 3 (for elements with atomic numbers up to $20$).

Atomic number

The quantity of protons present in the nucleus of an atom, defining the identity of the chemical element.

Mass number

The total sum of protons and neutrons contained within an atom's nucleus.