Why do elements take part in a chemical reaction?

Answer 1

Because the compounds produced are in a lower energy state (electrically) than the unreacted atoms.

OR

Energy has to be put into a compound to split it into its atomic components.

If you look at the "Noble Gasses" (Helium, Neon, Argon, Krypton etc) they do not react with other atoms to form compounds. This is because they have enough electrons orbiting their nuclei to "fill" or "complete" an entire electron shell - this is a very stable "low energy" position to be in.

Basically, when atoms form compounds, the atoms "share" their outermost electrons in an attempt to complete their electron shells (those with an extra electron sharing this with an atom that has too few).

Answer 2

The short answer is that atoms undergo nuclear reactions because they are unstable.

The slightly longer answer that there are interactions between the strong atomic force, the electromagnetic force, and the weak atomic force that causes nuclei to be unstable.

The strong atomic force holds protons and neutrons together. (It also holds quarks together to form protons and neutrons.) It is an attractive force. It is the strongest force in the universe, at least at the sub-atomic level.

The electromagnetic force holds nuclei and electrons together. It is both attractive, between protons and electrons, and repulsive, between protons and protons. This repulsion between protons is a chief contributor to the instability of larger nuclei. The reason for this is that both forces depend on distance, but the strong force is impacted more by distance than the electromagnetic force. As a result, in larger nuclei, (larger than lead=82), the electromagnetic force starts to win out, and make the nucleus unstable.

Thirdly, is the weak atomic force, which participates in energy exchange between particles. It causes the stability of the nucleus to be dependent on the ratio of protons to neutrons, and can cause radioactivity (instability) even in light nuclides, such as carbon-14.

Answer 3

Because they need to make sure they have 8 valance electrons