Protons and Neutrons Are Found in the Nucleus: Atomic Basics
Atoms are made of three basic particles: protons, neutrons, and electrons. The protons and neutrons are found in the nucleus, a small, dense core at the center of the atom, while the electrons orbit around it.
The Nucleus and Its Particles
The nucleus is incredibly small compared to the whole atom—if an atom were the size of a football stadium, the nucleus would be about the size of a pea. Protons carry a positive electric charge, and neutrons are electrically neutral. Both are roughly 1,800 times heavier than an electron, so nearly all of an atom’s mass is packed into the nucleus.
The number of protons in the nucleus determines which element an atom is. For example, every carbon atom has exactly six protons. The number of neutrons can vary, creating different isotopes of the same element. Carbon-12 has six neutrons, while carbon-14 has eight; both are still carbon because they each have six protons. The International Union of Pure and Applied Chemistry (IUPAC) defines elements based on their atomic number, which is the count of protons in the nucleus International Union of Pure and Applied Chemistry.
Neutrons serve a key role: they help hold the nucleus together. Protons repel each other because of their like charges, but the strong nuclear force, which acts between protons and neutrons, overcomes that repulsion. Without neutrons, most nuclei would fly apart.
A Worked Example: Sodium
Sodium has an atomic number of 11, so every sodium atom has 11 protons in its nucleus. The most common isotope, sodium-23, has 12 neutrons (11 + 12 = 23). This nucleus is stable and makes up nearly 100% of natural sodium. The 11 electrons outside the nucleus give sodium its chemical reactivity—they are easy to remove, which is why sodium forms positive ions (Na⁺) in compounds like table salt (NaCl).
Key Takeaways
- Protons and neutrons are found in the nucleus, the atom’s dense central core; electrons exist outside it.
- The number of protons in the nucleus defines the element, while the number of neutrons determines the isotope.
- Neutrons stabilize the nucleus by offsetting the repulsive force between positively charged protons.
- Almost all of an atom’s mass comes from the nucleus because protons and neutrons are much heavier than electrons.
