Short answer: an atom is a tiny piece of matter, like one atom of oxygen or gold. A quark is a much smaller particle that lives inside the center of an atom. Atoms are made of protons, neutrons and electrons, and the protons and neutrons are made of quarks.
The building ladder, from big to small
- Atom: the basic unit of an element, such as hydrogen or iron.
- Nucleus: the tiny core of the atom, made of protons and neutrons.
- Proton and neutron: each one is built from three quarks.
- Quark: as far as we know, one of the smallest building blocks of matter.
Electrons also sit inside the atom, but they move around the outside of the nucleus. Electrons are not made of quarks. They are a different kind of particle.
Quark vs atom: quick comparison
- Size: an atom is about one ten-billionth of a metre across. The nucleus is roughly 100,000 times smaller than the atom. A quark is smaller still, and nobody has measured a size for it.
- Parts: an atom has parts (protons, neutrons, electrons). A quark has no known parts.
- Seen alone? You can have a single atom by itself. A quark is never found alone. It is always stuck to other quarks.
- How many kinds? There are over 100 elements, so over 100 kinds of atoms. There are only six kinds of quarks.
- Can we see it? Special microscopes can show pictures of single atoms. Quarks can only be studied by smashing particles together in big machines.
A simple example: the hydrogen atom
Hydrogen is the simplest atom. It has one proton in the middle and one electron around it. That one proton contains three quarks: two “up” quarks and one “down” quark. So a hydrogen atom contains three quarks and one electron.
Common mistakes
- “Quarks are inside electrons.” No. Electrons are not made of quarks.
- “A quark is a small atom.” No. Quarks are parts of protons and neutrons, which are parts of atoms.
- “We have photos of quarks.” No. We find quarks from patterns in experiments, not from pictures.
Quick FAQ
Is a quark smaller than an atom?
Yes, by a huge amount.
How many quarks are in an atom?
Three for every proton and every neutron. A carbon atom with 6 protons and 6 neutrons has 36 quarks.
Can an atom exist without quarks?
Not in normal matter. Every nucleus has protons or neutrons, and those are made of quarks.
Keep reading: the six quark flavours, how the strong force holds quarks together, and what could be smaller than a quark. Also see quark-gluon plasma. Back to the science section