An element is a type of atom, defined by the number of protons in its nucleus. Copper — an element that is important in electronics — has 29 protons in its nucleus. On the other hand, hydrogen atoms have just one proton in the nucleus, an atom with two protons in the nucleus is helium, atoms with three protons are called lithium, and so on.

The number of protons in the nucleus of an atom is called the atomic number. Thus, the atomic number of hydrogen is 1, the atomic number of helium is 2, lithium is 3, and so on. Copper is atomic number 29, because it has 29 protons in its nucleus.

What about neutrons, the other particle found in the nucleus of an atom? Neutrons are extremely important to chemists and physicists. But they don't really play that big of a role in the way electric current works. Suffice it to say that in addition to protons, the nucleus of each atom (except hydrogen) contains neutrons — and in most cases, there are a few more neutrons than protons.

The third particle that makes up atoms is the electron. Electrons are what we're most interested in when we work with electricity because they are the source of electric current. They're unbelievably small; a single electron is about 200,000 times smaller than a proton.

To gain some perspective on that, if a single electron were the size of the period at the end of this sentence, a proton would be about the size of a football field.

Atoms usually have the same number of electrons as protons, and thus an atom of the element copper has 29 protons in a nucleus that is orbited by 29 electrons. When an atom picks up an extra electron or finds itself short of an electron, things get interesting because of a special property of protons and electrons called charge.