Covalent Bonding Lewis Structures

Bonding with Nonmetals When no metal is present to donate electrons, nonmetals can share electrons to fill their valence shells. F F Bond formation DECREASES total potential energy (energy lost), Bond Breakage INCREASES total potential energy (absorb energy)

Bonding with Nonmetals Each atom donates an un-paired electron to be shared in the covalent bond. F F circle new pair Both atoms have access to this new pair of atoms some of the time.

Multiple Covalent Bonds For atoms with more than one unpaired valence electron, multiple covalent bonds between the two atoms can form. S O Two atoms can form single, double, or triple covalent bonds.

Multiple Covalent Bonds Each bond represents a pair of electrons, one from each atom being bonded. H S N More bonds will bring the atoms closer together and the bond will be stronger (more energy required to break it). Strong bonds have low PE already, so more KE must be added to break them.

Lewis Structures Lewis structures show the atom symbols, covalent bonds, and unbonded electrons for covalent molecules. Cl

Drawing Lewis Structures 1) Count the total number of valence electrons in all atoms in the molecule. CO2 C: 4 O: 6 x 2 = 12 12 + 4 = 16 total val. e-

Drawing Lewis Structures 2) The least electronegative, non-hydrogen atom is placed in the center and the other atoms are written surrounding it. O C O

Drawing Lewis Structures 3) Draw single covalent bonds connecting the central atom to each outside atom. (subtract used electrons from total) O C O 16 - 4 12

Drawing Lewis Structures 4) Add electrons to fill outside atom valence shells. (substract used electrons from total) O C O 12 - 12

Drawing Lewis Structures 5) Check to make sure the central atom has a full octet. If not, shift pairs from outer electrons into bonds. O C O

Lewis Structure Practice 1) Draw a Lewis structure for NH3. H N H False H

Lewis Structure Practice 2) True or False: The image below is the correct Lewis structure for PF3. F P F True F

Lewis Structure Practice 3) Draw a Lewis structure for each of the following molecules: SiO2 H2O CH2F2 C2H4

CO NF SO HBr Naming Molecules Simple covalent molecules are named in the style of ionic compounds (cation then modified anion) based on relative electronegativity values. CO NF SO HBr

Naming Molecules Number Prefix 1 mono 6 hexa 2 di 7 hepta 3 tri 8 octo 4 tetra 9 nona 5 penta 10 deca

CO2 H2O NO3 Naming Molecules Since multiple possible element ratios exist, we add prefixes to the element names to indicate the subscripts. CO2 H2O NO3 The prefix “mono” is only used for the more electronegative (second) atom.

Naming Practice Name the following covalent molecules: SiO2 NO4 N2S3 P3O7 CO3