Subatomic Particle Properties

Three Properties That Distinguish Subatomic Particles

Atoms contain protons, neutrons, and electrons. Their charge, mass, and location determine how each particle affects an atom.

Compare these three properties:

charge, the electric sign of the particle
mass, how much the particle contributes to atomic mass
location, the region of the atom where the particle is found in the atomic model

Together, charge, mass, and location distinguish the three subatomic particles.

The 2022 CODATA review provides more precise values for these constants.

Subatomic Particle Model

Switch the mode below. Compare the main visual evidence: bending direction, mass-comparison height, and particle location inside the atom.

Subatomic Particle Property Map

Compare the charge, mass, and location of protons, neutrons, and electrons in one model.

Protons are positive, electrons are negative, and neutrons are neutral. In an electric field, charge sign controls the bending direction.

Proton: $+1$
Neutron: $0$
Electron: $-1$

Charge Determines the Direction of Bending

Electric charge determines how a particle responds to an electric field. A proton is positive, an electron is negative, and a neutron has no total charge.

The proton and electron have the same charge magnitude, but opposite signs:

e = 1.602176634 \times 10^{-19}\ \text{C}

That means:

a proton has charge $+e$
an electron has charge $-e$
a neutron has charge $0$

In an electric field, a charged particle experiences a force described by:

F = qE

The symbol $q$ is the particle charge, and $E$ is the electric field. If $q$ is positive, the force points with the field. If $q$ is negative, the force points the opposite way. If $q = 0$ , the particle is not bent by a simple electric field.

An electric field exerts a force on charged particles. A proton is pushed along the field, an electron in the opposite direction, and a neutron is not deflected in this simple model.

Mass and Acceleration

Subatomic particle masses are tiny, so we often use the unified atomic mass unit, written $\text{u}$ . It is defined from the mass of a ${}^{12}_{6}\mathrm{C}$ atom.

Particle	Relative charge	Relative mass	Absolute mass	Main location
Proton	$+1$	$1.0073\ \text{u}$	$1.67262 \times 10^{-24}\ \text{g}$	Nucleus
Neutron	$0$	$1.0087\ \text{u}$	$1.67493 \times 10^{-24}\ \text{g}$	Nucleus
Electron	$-1$	$0.00055\ \text{u}$	$9.10939 \times 10^{-28}\ \text{g}$	Space around the nucleus

Protons and neutrons have nearly the same mass, while an electron is much lighter than either of them.

A simple comparison is:

\frac{m_p}{m_e} \approx 1836

So one proton has about the same mass as $1836$ electrons. Protons and neutrons in the nucleus therefore provide almost all of an atom's mass.

Suppose the same force acts on a tennis ball and a bowling ball for the same amount of time. The tennis ball has less mass, so it undergoes a greater acceleration and a greater change in velocity. The balls represent only the difference in mass. Their shapes do not represent particle shapes. An electron responds more strongly than a proton to the same electric force because its mass is much smaller.

Particle Location and Chemical Role

Protons and neutrons remain in the nucleus, while electrons occupy the surrounding region. That difference determines which particle controls element identity, isotope mass, and chemical reactions.

Particle	Location	Common role in chemistry
Proton	Nucleus	Determines element identity.
Neutron	Nucleus	Adds mass and distinguishes isotopes.
Electron	Space around the nucleus	Strongly affects reactions and ion formation.

The number of protons determines the element. For example, an atom with $6$ protons is carbon. If the neutron number changes, the element is still carbon, but the isotope is different. If the electron number changes, the atom becomes an ion.

For a neutral atom, the number of protons and electrons is the same:

\text{neutral atom} \Rightarrow p^+ = e^-

This equation states that the total positive and negative charges balance. Proton and electron masses remain different.

Using Particle Properties in Atomic Symbols

Atomic symbols place three pieces of information around the element symbol. On Atomic Symbols, each number has a specific meaning:

the number of protons gives the atomic number
the number of protons plus neutrons gives the mass number
the difference between protons and electrons gives the ion charge

Use the three relationships together. Proton count determines element identity, proton plus neutron count determines mass number, and the difference between proton and electron counts determines the atom or ion charge.