Summary
Highlights
Atoms are extremely small, with a radius of approximately 1 x 10^-10 meters. This figure varies between different atoms. Atoms consist of a central nucleus surrounded by electrons.
The nucleus is tiny, less than 1/1000th the radius of the atom, but it concentrates almost all of the atom's mass. It contains positively charged protons and neutral neutrons, giving the nucleus an overall positive charge.
Electrons, which carry a negative charge, surround the nucleus in distinct energy levels. Energy levels further from the nucleus are at a higher energy than those closer to it.
Electrons can change energy levels by absorbing or emitting electromagnetic radiation. When an atom absorbs radiation, an electron moves from a lower to a higher energy level. When an atom emits radiation, the electron returns to a lower energy level.