#chemistry #electrons

Electronic configuration

• We can represent the structure of the atom in two ways: using diagrams called electron shell diagrams or by writing out a special notation called the electronic configuration (or electronic structure or electron distribution)

Electron shell diagrams

• Electrons orbit the nucleus in shells (or energy levels) and each shell has a different amount of energy associated with it

• The further away from the nucleus, the more energy a shell has

• Electrons fill the shell closest to the nucleus 

• When a shell becomes full of electrons, additional electrons have to be added to the next shell

• The first shell can hold 2 electrons

• The second shell can hold 8 electrons 

• For this course, a simplified model is used that suggests that the third shell can hold 8 electrons

  • For the first 20 elements, once the third shell has 8 electrons, the fourth shell begins to fill

• The outermost shell of an atom is called the valence shell and an atom is much more stable if it can manage to completely fill this shell with electrons 

The arrangement of electrons in shells can also be explained using numbers

• Instead of drawing electron shell diagrams, the number of electrons in each electron shell can be written down, separated by commas

• This notation is called the electronic configuration (or electronic structure)

  • E.g. Carbon has 6 electrons, 2 in the 1st shell and 4 in the 2nd shell

    • Its electronic configuration is 2,4

• Electronic configurations can also be written for ions

  • E.g. A sodium atom has 11 electrons, a sodium ion has lost one electron, therefore has 10 electrons; 2 in the first shell and 8 in the 2nd shell

    • Its electronic configuration is 2,8

• Formula : 2nSqaure