Covalent bond: Chemical bonding that results from the sharing of electrons between two atoms Covalent bonds share the electrons between the atoms equally (NONPOLAR) or unequally (POLAR).

Properties of Covalent Compounds Because covalent bonds are generally weaker than ionic bonds, the melting points and boiling points of covalent compounds are generally lower than those of ionic compounds. Many covalent compounds exist as gases at room temperature. Ionic bonds are rigid while covalent bonds are more like springs

Bond and Lone Pairs In Covalent Bonds valence electrons are distributed as shared or BOND PAIRS , and unshared or LONE PAIRS. • •• H Cl shared or bond pair lone pair (LP) This is called a LEWIS structure.

Steps for Building a Dot Structure Ammonia, NH3 1. Add up the number of valence electrons that can be used. H = 1 and N = 5 Total = (3 x 1) + 5 = 8 electrons *Ions: + subtract electron, - add electron, brackets 2. Decide on the central atom; never H,Why? If there is a choice, the central atom is the atom with lowest electronegativity or element with fewest atoms. Often, carbon is a central atom. Therefore, N is central on this one

Building a Dot Structure 3. Draw “skeleton” molecule. Form a single bond between the central atom and each surrounding atom (each bond takes 2 electrons, subtract these from total) H N 4. Distribute remaining electrons form LONE PAIRS to complete the octet as needed (or duet in the case of H). H •• N Note that N has a share in 4 pairs (8 electrons), while H shares 1 pair (2 electrons).

Building a Dot Structure Check to make sure there are 8 electrons around each atom except H. H should only have 2 electrons. This includes SHARED pairs. H •• N 6. Finally, CHECK THE NUMBER OF ELECTRONS IN YOUR MOLECULE! *If you have more electrons in the drawing than allowed, you must make double or triple bonds. *If you have less electrons in the drawing than you need, you have made a mistake!

Carbon Dioxide, CO2 1. Valence electrons = 2. Chose central atom. 3. Form single bonds. C 4 e- O 6 e- X 2 O’s = 12 e- Total: 16 valence electrons This leaves 12 electrons (6 pair). 4. Place lone pairs on outer atoms to give all atoms an octet. 5. Check to see that all atoms have 8 electrons around it except for H, which can have 2.

Carbon Dioxide, CO2 C 4 e- O 6 e- X 2 O’s = 12 e- Total: 16 valence electrons How many are in the drawing? 6. There are too many electrons in our drawing. We must form DOUBLE BONDS between C and O. Instead of sharing only 1 pair, a double bond shares 2 pairs. So one pair is taken away from each atom and replaced with another bond.

Double and even triple bonds are commonly observed for C, N, P, O, and S H2CO SO3 C2F4

Let’s Practice! CH3Br SO2 PBr3 C2H4 NO2-1

Molecular Nomenclature Prefix System (binary compounds) Recognize these because they’re made up of 2 nonmetals? Where are nonmetals found??? Add prefixes to indicate # of atoms. Omit mono- prefix on first element. 3. Change the ending of the second element to -ide.

Molecular Nomenclature PREFIX mono- di- tri- tetra- penta- hexa- hepta- octa- nona- deca- NUMBER 1 2 3 4 5 6 7 8 9 10

Special Rules with Mono If there is only one of the first element, then the prefix mono is not used. If there is only one of the second element, then the prefix mono is necessary. Ex. CO – Carbon Monoxide CO2 – Carbon Dioxide C2O – Dicarbon Monoxide

Also…. CH2 - Carbon Dihydride N3O6 - Trinitrogen Hexaoxide There is NO REDUCING for covalent compounds. What you see is what you get. If you reduced, you would change the chemical formula and ratio of the elements in the bond….Not good…. C2H4 - Dicarbon Tetrahydride CH2 - Carbon Dihydride N3O6 - Trinitrogen Hexaoxide NO2 - Nitrogen Dioxide

Molecular Nomenclature CCl4 N2O SF6 carbon tetrachloride dinitrogen monoxide sulfur hexafluoride

Molecular Nomenclature arsenic trichloride dinitrogen pentoxide tetraphosphorus decoxide AsCl3 N2O5 P4O10

Molecular Nomenclature The Seven Diatomic Elements (these seven elements always exist bonded in pairs) I2 Br2 Cl2 F2 O2 N2 H2 H N O F Cl Br I