What is an atom?

An atom is the smallest piece in an element and looks somewhat like this:

The blue area of the atom represents the nucleus which is made up of protons (positively charged) and neutrons (neutral). Meanwhile the green circles are the electrons (negatively charged) that orbit around the nucleus in shells or orbitals.

Note: This is an enlarged image of an atom for atoms are minute in nature.

Not only are atoms small, they also move.

Keep in mind that when energy is added, the atom moves faster because they gain more kinetic energy. This will be important when explaining 'Heat Transfer'

The Atomic Theory

An English chemist, named John Dalton was the first person to realize that atoms make up all of the matter around us (because it could explain the law of conservation and the law of constant composition).

The ideas of Dalton's atomic theory are as follows:

• All substances are made up of tiny indivisible particles.
• Each chemical element is made up of its own kind of particles, called atoms.
• The atom of a given element are alike in mass. Atoms of different elements differ in mass and properties.
• Atoms can neither be created or destroyed in a chemical or physical change.
• Atoms, when bonded together, form compounds.

However over time, some of Dalton's postulates have been disproven. An example would be that atoms can neither be created or destroyed. In real life however, the process of nuclear fusion and fission have disproven this postulate for atoms can be split into their subparticles.

Although some of his postulates have been discarded over the years (are no longer in use), others have been retained and incorporated into recent and later atomic theories.