Proton
A proton is a positively charged subatomic particle found in the nucleus of every atom, with a charge of +1 elementary charge and a mass of approximately 1.673 × 10⁻²⁷ kg (about 1 atomic mass unit). The number of protons in an atom's nucleus defines the element and is called the atomic number, which determines the chemical identity of the atom. Protons are composed of two up quarks and one down quark held together by the strong nuclear force.
Key Formula
Z = number of protons (atomic number)
LaTeX: Z = \text{number of protons}
| Symbol | Meaning | Unit |
|---|---|---|
| Z | Atomic number (number of protons) | dimensionless |
Worked Example
Problem
An atom has 8 protons in its nucleus. Identify the element and state its atomic number.
Solution
Step 1: The atomic number Z equals the number of protons. Z = 8 Step 2: Look up element with Z = 8 on the periodic table. Element with Z = 8 is Oxygen (O).
Answer
The element is Oxygen (O) with atomic number Z = 8.
Properties of the Proton
| Property | Value | Unit |
|---|---|---|
| Charge | +1 | Elementary charge (e) |
| Mass | 1.6726 × 10⁻²⁷ | kg |
| Mass (amu) | 1.0073 | u |
| Location | Nucleus | — |
| Composition | 2 up quarks + 1 down quark | — |
Interactive Tools
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Related Terms
Neutron
A neutron is an electrically neutral subatomic particle found in the nucleus of all atoms except ordinary hydrogen, with a mass of approximately 1.675 × 10⁻²⁷ kg, slightly greater than the proton. Neutrons contribute to the mass of the nucleus and play a crucial role in nuclear stability by reducing electrostatic repulsion between protons through the strong nuclear force. Atoms with the same number of protons but different numbers of neutrons are called isotopes.
Atomic Number
The atomic number (symbol Z) is the number of protons in the nucleus of an atom and uniquely identifies the chemical element — all atoms of the same element have the same atomic number. In a neutral atom, the atomic number also equals the number of electrons, which determines the element's chemical behavior, reactivity, and position on the periodic table. The atomic number ranges from 1 (hydrogen) to 118 (oganesson) for currently known elements.
Atomic Nucleus
The atomic nucleus is the small, dense, positively charged core at the center of an atom, containing protons and neutrons (collectively called nucleons) held together by the strong nuclear force. Although the nucleus is approximately 10⁻¹⁵ m (1 femtometre) in diameter — about 100,000 times smaller than the atom itself — it contains nearly all the atom's mass. Nuclear reactions, such as fission and fusion, involve changes to the nucleus and release enormous amounts of energy.
From Greek "proton" meaning "first". The proton was identified by Ernest Rutherford in 1917–1920, and the name was coined by Rutherford himself. The term reflects the proton's fundamental role as the defining particle of every element.