A proton is one of the three elementary particles that make up the nucleus of an atom. Although protons are very small, powerful electron microscopes have allowed scientists to observe and describe the structure of this particle that makes an element an element.

Significance

An atom is the basic building block of everything. Although there are smaller particles than the three elementary particles, protons can't be removed without changing the substance. Taking away or adding a proton changes the basic element--for example, adding a proton to a hydrogen atom turns it into a helium atom.

Features

Protons have a positive charge, just as electrons have a negative charge and neutrons have a neutral charge. Protons are always situated next to an equal number of neutrons in the center of the atom (known as the nucleus). Protons are constantly surrounded by orbiting electrons because opposite charges attract each other.

Appearance

A proton is, relatively speaking, a large, heavy particle of matter, approximately 1,836 times heavier than an electron. If you could see a proton, it would be surrounded by a sort of "halo" of one or more electrons.

Size

Atoms are very small; one hydrogen atom measures about 5 x 10 -8 mm although the particles within them are actually much farther apart than they are portrayed in illustrations. If an atom could be blown up to about the size of a word in this sentence, the electrons would actually be around a football field's distance away.

Misconceptions

Illustrations have envisioned protons in different ways, but nearly all of them portray protons as a smooth sphere. This doesn't necessarily mean that a proton would look this way if you could blow it up to macroscopic size. Protons, in fact, are too small to reflect photons (particles of light) and so cannot be seen in a conventional sense. Any visualization of a proton is therefore a construct made for convenience's sake.

Source:

Science Classes at John Jay College: Atomic Structure

Newton Ask A Scientist: Proton Mass

More Information:

ThinkQuest: The Atom