Physics Of Atoms: Moving Up To A Higher Energy Level

All matter is made of atoms. Atoms have a nucleus, which consists of protons and neutrons, and is surrounded by electrons. The nucleus is concentrated in a very small space, about 10-15 m. An entire atom is on the order of 10-10 m, so the electrons are relatively far from the nucleus, and, strangely enough, atoms are mostly empty space.

Physicists have found that the electrons traveling around the atomic nucleus can have only certain amounts of energy, called energy levels. In other words, the energy levels of atomic electrons are quantized. If electrons gain energy, they can move from one energy level up to a higher level, but these different energy levels are not continuous—they come in discrete steps. (Watch the animation in Figure 1, below, to see an electron gain energy and move up to a higher energy level.) This fundamental discovery is known as quantum mechanics. Quantum mechanics describes how an atom's electrons interact with electrons of other atoms and with photons.

Figure 1. In this animation, the red circle represents an atom's nucleus and the blue circle is an electron orbiting around the atom. The black rings are different energy levels the

(You can also see this in the animation in Figure 1, above.) Again, the electron moves from one allowed energy state to another. The lost energy can be carried away in the form of heat (vibrational energy) or in the form of light—when the electron reverts to a lower energy state, a photon of light is produced. The photon produced will have an energy equal to the difference between the electron's initial high energy state and the later lower-energy state. For visible light, we perceive these differences in photon energy as differences in the color of the light. Because different types of atoms have different gaps between their energy levels, they make light of different colors when their electrons lose