Atomic structure orbitals and electronic configurations

It is important to understand the location of electrons, as it is the arrangement of the electrons that creates the bonds between the atoms, and chemical reactions are just that to form new bonds. Electrons are involved in the chemical bonding and reactions of an atom. Electrons are said to occupy orbitals in an atom. 

An orbital is a region of space that can hold two electrons. Electrons do not move freely in the space around the nucleus but are confined to regions of space called shells. Each shell can contain up to 2n electrons, where n is the number of the shell. Each shell contains subshells known as atomic orbitals. The first shell contains a single orbital known as the l orbital. The second shell contains one 2s and three 2p orbitals. These three 2p orbitals are designated as 2p, 2py and 2p. The third shell contains one 2s orbital, three 3p orbitals and five 2d orbitals. Thus, the first shell can hold only two 

SheU Total number of shell electrons Relative energies of shell electrons  

The electronic configuration of an atom describes the number of electrons that an atom possesses, and the orbitals in which these electrons are placed. The arrangements of electrons in orbitals, subshells and shells are called electronic configurations. Electronic configurations can be represented by using noble gas symbols to show some of the inner electrons, or by using Lewis structures in which the valence electrons are represented by dots. 

Valence is the number of electrons an atom must lose or gain to attain the nearest noble gas or inert gas electronic configuration. Electrons in the outer shells that are not filled are called valence electrons. 

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