How do Covalent bonds form

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

Molecular Compounds

◦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.

Polar bonds in molecules

◦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