What Are the 3 Subatomic Particles of an Atom? Protons, Neutrons, and Electrons
The three subatomic particles commonly described in an atom are protons, neutrons, and electrons. Protons have a positive electric charge, neutrons have no electric charge, and electrons have a negative charge. Protons and neutrons are in the nucleus at the center of the atom. Electrons occupy regions around the nucleus.
The particles have different roles. The number of protons determines which element an atom is. Neutrons contribute to its mass and distinguish isotopes of the same element. Electrons determine an atom’s charge and take part in chemical bonding.
| Particle | Charge | Location | Main role |
|---|---|---|---|
| Proton | Positive | Nucleus | Determines the element |
| Neutron | None | Nucleus | Adds mass; contributes to nuclear stability |
| Electron | Negative | Around the nucleus | Determines charge and chemical bonding |
Protons: the element’s identity
A proton is a positively charged particle in the nucleus. Its charge has the same magnitude as an electron’s charge, but the opposite sign. A proton is also much more massive than an electron, with a mass roughly 1,836 times greater.
An atom’s atomic number is its number of protons. That number defines the element: every hydrogen atom has one proton, and every carbon atom has six. If the number of protons changes, the atom becomes a different element.
Protons help give the nucleus its mass. They also repel one another because they carry the same positive charge. The forces within the nucleus help hold its particles together.
Neutrons: mass and isotopes
A neutron is a neutral particle in the nucleus. It has a mass similar to a proton’s, so neutrons contribute substantially to an atom’s mass without adding electric charge.
Atoms of the same element can have different numbers of neutrons. These forms are called isotopes. For example, hydrogen has isotopes with zero, one, or two neutrons. Each remains hydrogen because each has one proton.
Neutron count is useful for identifying an isotope and understanding the nucleus. It usually has little effect on an atom’s chemical behavior, which is mainly shaped by its electrons.
Electrons: charge and bonding
An electron has a negative charge and a much smaller mass than a proton or neutron. Electrons occupy regions around the nucleus called orbitals. These are areas where an electron is likely to be found, not fixed paths circling the nucleus.
A neutral atom has the same number of electrons as protons. Their opposite charges cancel, leaving the atom with no net charge. If an atom gains or loses electrons, it becomes an ion. For example, losing an electron gives an atom a positive charge; gaining one gives it a negative charge.
Electrons, especially those in the outer part of an atom, take part in chemical bonds. Their arrangement helps explain why elements have different chemical properties.
Example: a neutral sodium atom
Sodium has an atomic number of 11, so every sodium atom has 11 protons. A neutral sodium atom also has 11 electrons. In the isotope sodium-23, the mass number is 23. The mass number counts protons and neutrons together, so:
23 − 11 = 12 neutrons
A sodium ion with a charge of +1 still has 11 protons and, if it is sodium-23, 12 neutrons. It has lost one electron, leaving it with 10. The change in electron count alters the atom’s charge; it does not change its element or isotope.
Atomic number, mass number, and atomic mass
These terms refer to different quantities:
- Atomic number is the number of protons.
- Mass number is the total number of protons and neutrons in a particular isotope.
- Atomic mass on a periodic table is generally a weighted average based on the isotopes found in a sample of an element. It is often not a whole number.
For an isotope, subtracting the atomic number from the mass number gives the number of neutrons. For example, carbon-12 has six protons and six neutrons. The “12” is its mass number, not the number of protons.
The NIST Atomic Data for the Elements provides reference data for elements and their isotopes. The U.S. Department of Energy also offers a conceptual overview of the atom.
Key Takeaways
- The three subatomic particles commonly described in an atom are protons, neutrons, and electrons.
- Protons are positive, neutrons are neutral, and electrons are negative.
- The proton count determines the element; the neutron count distinguishes its isotopes.
- Electrons determine an atom’s charge and take part in chemical bonding.
- A neutral atom has equal numbers of protons and electrons. For a specific isotope, subtract the proton count from the mass number to find the neutron count.
