shell science definition

a. The usually hard outer covering of certain animals, such as mollusks, insects, and turtles.

b. The hard outer covering of a bird's egg.

c. The hard outer covering of a seed, nut, or fruit.

a. A set of electron orbitals that have nearly the same energy. Electrons in outer shells have greater energy than those in shells closer to the nucleus. Elements in the Periodic Table range from the lightest elements with electrons normally occupying one shell (hydrogen and helium) to the heaviest, with electrons in seven shells (radium and uranium, for instance). See more at atomic spectrum, orbital, subshell. See Note at metal.

b. Any of the stable states of other particles or collections of particles (such as the nucleons in an atomic nucleus) at a given energy or small range of energies.