Electron Configurations

How are the seats in your classroom arranged? Are they lined up neatly in rows, or are they grouped in clusters? A configuration is an arrangement of objects in a given space. Some configurations are more stable than others, meaning that they are less likely to change. The position of the gymnast on the balance beam in Figure 16 is not very stable because the beam is only 10 centimeters wide.

An electron configuration is the arrangement of electrons in the orbitals of an atom. The most stable electron configuration is the one in which the electrons are in orbitals with the lowest possible energies. When all the electrons in an atom have the lowest possible energies, the atom is said to be in its ground state.

For example, lithium is a silvery-white metal with an atomic number of 3, which means that a lithium atom has three electrons. In the ground state, two of the lithium electrons are in the orbital of the first energy level. The third electron is in an orbital of the second energy level.

If a lithium atom absorbs enough energy, one of its electrons can move to an orbital with a higher energy. This configuration is referred to as an excited state. An excited state is less stable than the ground state. Eventually, the electron that was promoted to a higher energy level loses energy, and the atom returns to the ground state. Helium, neon, argon, krypton, and xenon atoms returning from excited states to the ground state emit the light you see in “neon” lights.