Chapter - 3

Pages Covered - 52-56

• Through this sharing, each atom gains a share in two electrons. This is the number of electrons in the outer shell of helium

• The main features of covalent bonding are:

  • the bond is formed by the sharing of a pair of electrons between two atoms, leading to noble gas electronic configurations

    
    

  • each atom contributes one electron to each bond

    
    

  • molecules are formed from atoms linked together by covalent bonds.

• A dot-and-cross diagram can be drawn showing the outer electrons only (Figure 3.6a), because the inner electrons are not involved in the bonding.

• In covalent compounds, bonds are again made by sharing electrons between atoms. In simple molecules, the atoms combine to achieve a more stable arrangement of electrons

Physical Properties

• They have low melting points and boiling points and are often liquids or gases at room temperature

• They show poor electrical conductivity.

• Reasons

  • They are made of simple covalent molecules. The forces between the molecules (intermolecular forces) are only very weak. Not much energy is needed to move the molecules further apart.

  • There are no free electrons or ions present to carry the electrical current.