Sizes of Atoms and Nuclei

It is very hard for anyone, even a nuclear physicist, to really understand how small something like the atom or its nucleus really is. The only good way to visualize it is to make a comparison to the relative sizes of things we see in our daily life.

Really large distances, like the 1000 miles (1600 km) between Florida and Michigan, are difficult to imagine. That cross-country distance is a factor of about 1,000,000 times larger than a person is tall.

Most people can see the period at the end of a sentence (one pixel in size) with little difficulty. So a really tiny object is about a factor of 20,000 times smaller than a person.

Combining these, we can say that if an atom were the size of the period at the end of a sentence or a pixel on your screen, a person would be 1000 miles tall! That is how small the atom is.

If an atom were the size of a football stadium, with the electrons out around the upper deck, the nucleus down at midfield would be smaller than the coin flipped at the start of the game.

Index to Graphical Examples

This is an ordered list of the size examples included in this section. They can be followed in sequence by using the menu list up above. There are also some side trips possible in this hyper-textbook, but you can always use the menus to get back to one of these starting points.

Quarks are, as far as we know, the smallest building blocks of matter. It takes 3 quarks to make up a proton or neutron. We call protons and neutrons "nucleons" to indicate that they are what nuclei are made of.
Nucleons, another name for protons and neutrons, are made up of quarks. One or more nucleons bound together form an atomic nucleus.
A nucleon is the smallest object we know of that has internal structure. Nuclear physicists study the internal stucture of nucleons as well as the structure of nuclei.
The Nucleus is a group of nucleons (protons and neutrons) held together by the strong nuclear force. The nucleus sits at the center of an atom, and the number of protons in the nucleus determines which element the atom will be.
The Atom consists of electrons bound to a nucleus by electrical forces. Because the electrical force is much weaker than the nuclear force, an atom is almost 100,000 times larger than the nucleus.
Cells are what every living thing is made of. A cell is held together by chemical forces between molecules, which are collections of atoms. A cell is so small that we need a powerful microscope to see it, but a cell is as much as 100,000 times larger than an atom.
People are made up of billions of cells. To place relative sizes in perspective, a person is almost 100,000 times larger than a cell. There are about 10,000,000,000,000 cells in the human body!

This means the step down in size from studying a person to studying a cell (something most people have some idea about from using a microscope) is about the same as the step down from cells to atoms or from atoms to nuclei.

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