|  | 4.1 | Basics of Electricity
| 4.1.2 | Creating stable atoms

One of the laws of nature, called Coulomb's Electric Force Law, states that opposite charges react to each other with a force that causes them to be attracted to each other. Like charges react to each other with a force that causes them to repel each other. A force is a pushing or pulling motion. In the case of opposite and like charges, the force increases as the charges move closer to each other.

Examine Bohr's model of the helium atom. If Coulomb's law is true, and if Bohr's model describes helium atoms as stable, then there must be other laws of nature at work. How can they both be true?

1. Coulomb's Law - Opposite charges attract.
2. Bohr's model - Protons are positive charges, and electrons are negative charges.

Question 1: Why don't the electrons fly in towards the protons?

1. Coulomb's Law - Like charges repel.
2. Bohr's model - Protons are positive charges. There is more than 1 proton in the nucleus.

Question 2: Why don't the protons fly away from each other?

The answers to these questions is that there are other laws of nature that must be considered. Following are the answers to each of the above questions.

Answer 1: The electrons stay in orbit, even though they are attracted by the protons. They have just enough velocity to keep orbiting, just like the moon around the Earth, and to not let themselves be pulled into the nucleus.

Answer 2: The protons do not fly apart from each other because of a nuclear force that is associated with neutrons. The nuclear force is an incredibly strong force that acts as a kind of glue to hold the protons together.

The protons and neutrons are bound together by a very powerful force; however, the electrons are bound to their orbit around the nucleus by a weaker force. Electrons in certain atoms can be pulled free from the atom, and made to flow. This is electricity - a "free flow of electrons".