Shared Electrons Sometimes atoms achieve a stable configuration by sharing electrons Covalent bonding occurs when atoms share a pair of valence electrons Each pair of shared electrons is a “bond” The attractions between the shared electrons and the protons in each nucleus hold the atoms together Covalent bonds tend to join nonmetals to nonmetals (high ionization energies)

Visualizing Covalent Bonds Lewis/Electron Dot Each pair of shared electrons is shown as two dots located between the atoms Structural Diagrams Each pair of shared electrons is shown as a dash connecting the atoms

Molecules and Multiple Bonds A molecule is a neutral group of atoms connected by one or more covalent bonds Many non-metallic elements exist in nature as diatomic molecules (go to 7, make a 7, add H) Atoms can share multiple pairs of electrons H 2 – single O 2 – double N 2 – triple

Unequal Sharing When unlike atoms covalently bond, one atom may have a stronger attraction for the electron This results in a polar covalent bond one atom slightly more positive one atom slightly more negative

Polar Molecules Depending on the type of atoms and the shape of the molecule, polar bonds can create a polar molecule CO 2 is not polar H 2 O is polar Attractions between polar molecules are greater than those between non-polar molecules The “hydrogen bond” is an important bond connecting water molecules