# The Anatomy of Atoms – Shells and Sub-Shells

The earth and the things on earth are very fascinating, we study them to understand how things are made and how did we come about.

In today’s article, we are going to talk about the shells and sub-shells of atoms, to understand how electrons are filled in the shell for a particular element on the periodic table. The reactivity of a particular atom or its tendency to form chemical bonds with other atoms, is determined by the number of electrons that a particular atoms possesses on its outermost shell.

The valance shell of an atom is its outermost shell, and only valence electrons are found at this shell energy level. When the valance shell of an atom is full with valence electrons, that atom is said to be most stable and least reactive.

The octet rule states that in order for an element, which is important in biology, to be stable, it must have eight electrons on its valence shell. Shells have another level of subdivision, known as sub-shells, which are equal to the number of shell present in an atom. A sub-shells can be found on shell 1, while two sub-shells are found on shell two.

The letters s, p, d and f are used to describe the various types of sub-shells an atom can have, and each of the different types of sub-shells have a maximum of electrons that they can hold. The letters also represent the shape of an orbital, we’ll discuss this later on.

 Sub-shells type # of electrons s 2 p 6 d 10 f 14

The lowest energy level is the s sub-shell while the higher-energy level is the f sub-shell. The number of sub-shells found in a shell depends on the number of that shell, take a look at the table bellow.

 Shell # n # of sub-shells N = 1 1s sub-shell N = 2 2s and 2p N = 3 3s, 3p, 3d

As you may notice on the table above the possible number of electrons a sub-shells can have depends on the shell number. Therefore the 1s sub-shells, which is in the first shell, would contain two electrons.

The 2s sub-shell would contain 2 electrons while the 2p sub-shell would have 6 electrons, which would give the second shell the ability to have 8 possible electrons.

Orbitals are found within sub-shells, and it is the region space, where an electron would be found. Every orbital has two electrons, therefore, the s sub-shell would have one orbital, while the p sub shell would have three orbitals.

A distinct shape belongs to each of the orbitals, a spherical shape belongs to the s orbital which is in the s sub-shell. The p orbitals, which are in the p sub-shells have a two-lobed shape, while a four-lobed shape belongs to the d orbitals, which is in the d sub-shells.

There is a 95 percent probability, that an electron would be found, within an orbital, which is depicted as a three-dimensional region.

A combination of numerals and letters are used to designate atomic orbitals, specific properties of the electrons, which are associated with the orbitals are represented by the combination of these numerals and letters. 1s, 2p, 3d, 4f represent the energy level as well as the relative distance an electron is from the nucleus. The numerals in front of the letters is known as the principal quantum numbers, which describes the size of the orbital. The shape of the orbital is designated by the letters s, p, d, and f.