 The chemical bond formed when 2 atoms share electrons, usually between 2 nonmetals

◦ Most nonmetals can bond with another atom of the same element

◦ The force that holds atoms together in a covalent bond is the attraction of each atom’s nucleus for the shared pair of electrons

 A MOLECULE IS A NEUTRAL GROUP OF ATOMS JOINED BY COVALENT BONDS.

◦ Except for Hydrogen, the number of covalent bonds that nonmetals form equals the number of electrons needed to make a total of 8, hydrogen only needs 2, Figure 15, page 167

◦ Double and triple bonds can form when atoms share more than one pair of electrons, double 2 pairs, triple 3 pairs. Figure 16, page 168

 IS a compound that is composed of molecules that are covalently bonded

◦ Have lower melting points and boiling points and they do not conduct electricity when dissolved in water. Math skills, page 169

 Less heat is needed to break a covalent bond, that’s why most molecular compounds are liquids or gases at room temperature

 Do not conduct electricity because no charged particles are available to move. Even when they are liquids they are poor conductors

 Unequal Sharing of electrons

◦ Atoms of some elements pull more strongly on shared electrons than do atoms of other elements. As a result, the electrons are pulled more toward one atom, causing the bonded atoms to have slight electrical charge.

 These charges are not as strong as ions

 Polar bonds: A covalent bond in which electrons are shared unevenly

 Non-polar bond: covalent bond in which the electrons are shared equally.  See figure 17, page 170

◦ A molecule with non-polar bonds will itself be non-polar. But, a molecule may contain polar bonds and still be non-polar overall.

◦ A carbon dioxide molecule is a non- polar molecule because it’s a straight line shape. In contrast a water molecule is polar because of its bend shape. The bent shape allows the O end to have a slight negative charge and the H₂ end to have a slight positive charge

◦ Attraction between molecules ◦ Polar molecules require more energy to break the bond than non-polar molecule