What is the number of electron shells in Barium?
Barium, Atomic Number 56, is an alkaline earth metal that does not occur in its pure form naturally as it reacts with air and oxidizes. Barium is a soft metal with a high gravity and was mainly used to pull the last air out of vacuum tubes. An alloy of Barium is also used in Spark Plug wiring, and it is also used in fireworks, oil well drilling, and X-Ray imaging.
An Electron Shell is the orbit around the nucleus occupied by two or more electrons -- only Hydrogen has a single electron in its shell. Since the electrons orbits so fast, they create an essentially solid surface and are referred to as a "shell." The electron shells determine how the element reacts with others atomically and chemically; the outer shells are more easily broken from the nucleus and so have a greater effect on reactivity.
Barium has 6 electron shells with an equal sequence of electrons in each; the progression is: 2 - 8 - 18 - 18 - 8 - 2. The electron shells are therefore progressively equal in thickness and number of particles from inner to outer shells.