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

1-mono2-di3-tri4-tetra5-penta

6-hexa7-hepta8-octa9-nona10-deca

Examples: CO2 is carbon dioxideCO is carbon monoxide

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

PlanarBent

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

chargeElectronegativity 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 & CovalentCharacteristic 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 High to Low

Electrical conductivity in aqueous solution

Good conductor Poor to nonconducting