Subatomic Particles
Middle School
Definition
The particles that make up an atom: positively charged protons and neutral neutrons in the nucleus, and negatively charged electrons surrounding it. Their numbers determine an element's atomic number, mass, and chemical properties.
Worked examples
A carbon atom has 6 protons, 6 neutrons, and 6 electrons.
The protons and neutrons cluster in the nucleus; the electrons orbit around it.
\(\)Atomic number\( = \)number of protons\( = 6\); \(\)Mass number\( \approx 6 + 6 = 12\)
Protons define the element; protons plus neutrons give the mass number.
Common mistakes
- Electrons are in the nucleus with protons and neutrons → Electrons orbit the nucleus; only protons and neutrons are inside The nucleus contains protons and neutrons; electrons occupy the space around it.
- Neutrons have a positive charge → Neutrons are neutral (no charge); protons are positive Neutrons have no charge—only protons are positive and electrons are negative.
- The mass number equals the number of protons only → Mass number = protons + neutrons Electrons have negligible mass; the mass number counts protons and neutrons together.
Where you'll use it next
You'll use subatomic particles to understand isotopes, ions, radioactive decay, and nuclear reactions in chemistry and physics, plus electron configuration and bonding.
See also
Reviewed by Pat Cheng, M.Ed. — StudyPug Curriculum Lead · Last updated June 6, 2026