2.3 Electronic structure and the Periodic Table

Page 1

Electron Shells

Electron move so rapidly that we cannot tell where they are at any point in time so we make a simple model to represent it. We imagine in spherical position having circular around the nucleus these orbit are called shells or energy levels.

The first shell is nearest to the nucleus and can hold a maximum of two electrons. The next shell out can hold a maximum of eight electron and if third shell has eight electron the fourth shell start fill up.

The arrangement of the electrons in shells is called the electronic structure or electron configuration. In sodium there 2 electron on first shell 8 on second and 1 on third so electron configuration of sodium as 2,8,1

Arranging the electrons

The horizontal row in the Periodic Table are called period and as you move across a period each element has one more electron to fit into its outer shell.

The vertical column in the periodic is call a group you can see they have same number of electron on their outer shell. These is called the Valency electron or outer shell.

The chemical properties of an element depend of valence electrons that why element in same group have same properties.

Page 2

The Noble Gas Structure

When compounds are formed by combing element, the electron in the outer shell are transferred and shared.

The noble gases, have full outer shell of electron. This type structure is very stable the atom can't lose or gain electron very easily.

This structure make the noble gases very unreactive so they do not combine with other element to form compounds.

When atoms of other element combine, the compound formed have noble gas structure of full electron shells around each atom