What is an atom?
An atom is the smallest unit of matter that retains the identity of a chemical element. It consists of a dense central nucleus containing protons and neutrons, surrounded by a cloud of electrons.
Subatomic particles
- Protons (p⁺): Positively charged particles in the nucleus. The number of protons defines the element (atomic number Z).
- Neutrons (n⁰): Neutral particles in the nucleus. Neutrons = Mass number (A) − Atomic number (Z).
- Electrons (e⁻): Negatively charged particles orbiting the nucleus. In a neutral atom, electrons = protons.
How to find protons, neutrons, and electrons
Protons = Atomic Number (Z)
Neutrons = Mass Number (A) − Atomic Number (Z)
Electrons = Protons − Charge
For ions, the charge modifies the electron count. A positive charge (cation) means fewer electrons; a negative charge (anion) means more electrons.