Covalent Compounds Contain 2 or more nonmetals. Made of molecules—NOT IONS. 2 nonmetals can combine in more than 1 way! CO2 is a gas that we breathe out. CO is a colorless, odorless, & deadly gas Both are carbon oxides, but it is important to distinguish between them.
Naming Covalent The number of each element (subscript) is written as a prefix in the both parts of the name. Change the ending to –ide on the 2nd element Examples: CO2 is carbon dioxide CO is carbon monoxide 1-mono 2-di 3-tri 4-tetra 5-penta 6-hexa 7-hepta 8-octa 9-nona 10-deca IMPORTANT: The mono prefix is omitted only on the first element. *On the back of your P.T.
Formulas of Covalent The prefixes on each element tell you the subscripts in the formula Example: tetraiodine nonoxide I4O9
Lets try some examples Given the formula, name the following molecular compounds. N2O Dinitrogen monoxide PCl3 Phosphorus trichloride SF6 Sulfur hexafluoride CS2 Carbon disulfide
More examples Given the name, what’s the formula for the following compounds. Nitrogen trifluoride NF3 Disulfur dichloride S2Cl2 Dinitrogen tetroxide N2O4 Phosphorus pentafluoride PF5
Properties of Covalent Compounds Chapter 8
Molecular Compounds Molecular = Covalent In a covalent bond, electrons are shared Diatomic molecule—a molecule consisting of 2 atoms Hydrogen = H2 N2 O2 F2 Cl2 Br2 I2
Properties Have lower melting/boiling points than ionic Most are gases or liquids at room temp. Composed of 2 (or more) nonmetals When writing a molecular formula, the subscripts are not always in the lowest ratio. Ex. H2O2
Covalent Bonding Molecules can form single, double, and triple bonds Single: share 1 pair of e- (2 e-) Shown as a single line Double: share 2 pairs of e- (4 e-) Shown as a double line Triple: share 3 pairs of e- (6 e-) Shown as a triple line Acetone
Bond Strength Many covalent compounds are more stable than the atoms alone. Bond Dissociation Energy—the energy required to break the bond between 2 covalently bonded atoms A large dissociation energy corresponds to a strong covalent bond
Bonding Theories VSEPR Theory: Valence Shell Electron Pair Repulsion The repulsion between e- pairs causes the shape of molecules to adjust so e- pairs are as far apart as possible
Molecular Shapes Linear Trigonal Planar Bent Pyramidal Tetrahedral Trigonal Bipyramidal Octahedral Square Planar T-Shaped
Polarity and Molecules Covalent Bonds can be polar or nonpolar Nonpolar—formed when e- are shared equally between 2 atoms Bonds can be nonpolar in 2 ways Nonpolar covalent bonds Ex. Diatomic elements: H2 N2 O2 F2 Polar Bonds due to symmetry CH4
Polar Bonds Formed when e- are shared unequally between 2 atoms The more electronegative atom attracts e- more strongly and gains a slightly negative charge The less electronegative atom has a slightly positive charge Electronegativity Differences & Bond Types Electronegativity Difference Range Bond Type 0.0-0.4 Nonpolar Covalent 0.4-1.0 Slightly Polar Covalent 1.0-2.0 Very Polar Covalent ≥2.0 Ionic
Characteristics of Ionic & Covalent Representative unit Formula Unit Molecule Bond formation e- transfer (gained or lost) e- shared Type of elements Metal + Nonmetal (& polyatomic ions) Nonmetal + Nonmetal Physical state Solids Solid, liquid, gas Melting Point High Low Solubility in water High to Low Electrical conductivity in aqueous solution Good conductor Poor to nonconducting