What Are the Three Atomic Particles That Build Every Atom?
The three basic particles in an atom are protons, neutrons, and electrons. Protons and neutrons make up the central nucleus. Electrons occupy regions of space around it. Each particle has a distinct electric charge and role.
Protons determine which element an atom is. Neutrons affect its mass and nuclear stability. Electrons shape its chemical behavior, including how it bonds with other atoms. The Encyclopaedia Britannica entry on atoms describes this structure: a nucleus of protons and neutrons surrounded by electrons.
| Particle | Electric charge | Where it is found | Main role |
|---|---|---|---|
| Proton | +1 | Nucleus | Determines the element |
| Neutron | 0 | Nucleus | Adds mass and affects nuclear stability |
| Electron | −1 | Around the nucleus | Influences bonding and chemical behavior |
The charge values in the table are relative charges. In a neutral atom, the number of protons equals the number of electrons, so their positive and negative charges balance. An atom with unequal numbers of protons and electrons has a net charge and is called an ion.
Protons determine the element
A proton has a positive charge and a mass of about one atomic mass unit. The number of protons in an atom is its atomic number. This number defines the element: every carbon atom has six protons, and every sodium atom has eleven.
Changing the number of protons changes the element. Because this requires a change in the nucleus, it is a nuclear change, not an ordinary chemical reaction. Chemical reactions rearrange electrons and bonds. They do not normally change the number of protons in an atom’s nucleus.
Protons are among the particles called nucleons, along with neutrons. They are not fundamental particles: protons and neutrons are made of smaller particles called quarks. Electrons, by contrast, are considered fundamental particles. The Encyclopaedia Britannica entry on subatomic particles describes this distinction.
Neutrons affect mass and nuclear stability
A neutron has no electric charge and has a mass close to that of a proton. It is found in the nucleus. Neutrons add to the nucleus’s mass and affect whether a particular nucleus is stable.
Protons have positive charges, so they repel one another electrically. The strong nuclear force acts between protons and neutrons at very short distances and helps bind the nucleus. The balance between these forces, along with the number of each type of nucleon, influences nuclear stability. Neutrons contribute to this balance; they do not simply “hold the nucleus together.”
Atoms of the same element can have different numbers of neutrons. These forms are called isotopes. They have the same number of protons, so they remain the same element, but their nuclei have different masses. For example, carbon-12 has six protons and six neutrons, while carbon-14 has six protons and eight neutrons.
Electrons shape chemical behavior
An electron has a negative charge. It is much lighter than a proton, with a mass about 1/1836 of a proton’s mass. Electrons do not travel around the nucleus like planets in fixed paths. Instead, they occupy quantum states described by probability distributions. An orbital is a region where an electron is likely to be found.
The arrangement of an atom’s electrons affects how it interacts with other atoms. Electrons in the outer part of an atom, often called valence electrons, have a large role in chemical bonding. Atoms can share or transfer electrons to form chemical bonds. They can also gain or lose electrons to become ions.
Electrons can move between allowed energy states by absorbing or emitting energy. When they emit light, the wavelengths depend on the atom’s energy levels. This is one reason atomic spectra can identify elements. The NIST Atomic Spectra Database provides information on atomic spectral lines.
One example: carbon-12
A neutral carbon-12 atom has six protons, six neutrons, and six electrons. Its atomic number is six because it has six protons. Its mass number is twelve, the total number of protons and neutrons.
If carbon-12 loses one electron, it becomes a positively charged ion. Its nucleus stays the same, so it is still carbon-12. If one neutron is added, the nucleus becomes carbon-13. It is still carbon because it has six protons, but it is a different isotope.
Changes to the particle count have different effects: changing the proton count changes the element; changing the neutron count changes the isotope; changing the electron count changes the atom’s charge.
Key Takeaways
- The three basic atomic particles are protons, neutrons, and electrons.
- Protons and neutrons are in the nucleus; electrons occupy regions around it.
- The number of protons determines the element.
- Isotopes of an element have different numbers of neutrons.
- In a neutral atom, the number of electrons equals the number of protons.
