Chapter 6: Chemical BondingCovalent Focus

6.1 Intro to Bonding

6.2 Lewis Structures

6.3 Covalent Formulas

6.1 Intro to BondingLearning Targets◦Describe and explain chemical bonding.

◦Describe ionic and covalent bonding.

6.1 Intro to BondingChemical Bond:

Force of attraction between two atoms

Due to mutual attraction of nuclei for electrons

6.1 Intro to BondingWhy do atoms form bonds?

Bonds allow atoms to become more stable by achieving lower energy Forming a bond releases energy Breaking a bond absorbs energy

Atoms gain or lose electrons to achieve noble gas configuration (full shell)

6.1 Intro to BondingOctet Rule: ◦Atoms tend to gain, lose, or share electrons

to get 8 valence electrons in order to achieve a noble gas configuration

◦Li◦O◦Ne◦C

6.1 Intro to BondingElectronegativity

Measures how strongly an atom pulls electrons towards it

6.1 Intro to BondingWhat type of bond?

Metals-metals: Metallic

Metal-nonmetal: Ionic

Nonmetal-nonmetal: Covalent Polar if atoms are different from each other

6.1 Intro to BondingClassify each of the following bonds:◦1. H –C

◦2. N—N

◦3. Cu—Zn

◦4. Cs—F

◦5. C—F

6.1 Intro to BondingIonic Bond

Bond formed by attraction between cation and anion One atom loses e-, one gains e-

6.1 Intro to BondingProperties of Ionic Compounds1. Crystalline

Orderly arranged pattern of cations and anions

2. Solid

3. High Melting/Boiling Points

6.1 Intro to Bonding4. Hard and Brittle

5. White or Bright colors

6. Dissolve in Water

7. Conduct electricity Break apart into ions in water

6.1 Intro to BondingCovalent bond:

Two atoms share electrons to gain an octet

Polar covalent: Bond formed by two elements that

have different electronegativity Electrons spend more time with one atom Slight charges on atoms Dissolve in polar solvents (water, ethanol)

6.1 Intro to BondingNonpolar covalent:

Bond formed by two elements that have the same or similar electronegativity

Electrons spend equal time with each atom No charge on atoms Dissolve in nonpolar solvents (hexane)

6.1 Intro to BondingProperties of Covalent Compounds1. Crystalline or Amorphous2. All phases 3. Soft4. Low melting/boiling point

6.1 Intro to Bonding5. Dull Colors

6. Soluble based on polarity Polar dissolve; Nonpolar do not

7. Nonconductors

6.1 Intro to BondingMetallic Bond

Positive nuclei (cations) exist separately in a sea of electrons

6.1 Intro to BondingProperties of Metals◦1. Conduct heat and electricity

◦2. Malleable

◦3. Ductility

◦4. Lustrous

6.2 Lewis StructuresLearning Targets:

Draw Lewis dot structures for covalent molecules.

Determine the polarity of a molecule.

Use VSEPR to determine shapes of molecules.

6.2 Lewis StructuresLewis Dot Structures

Representation of molecules using nonbonding e-, bonding e-, and atoms

Bonding Pair 2 shared electrons

Lone Pair 2 electrons not in a bond

6.2 Lewis Structures

1. Br2

2. N2

3. H2O

4. CH3I

6.2 Lewis Structures

5. HNO

6. C2H6

7. C2H4

6.2 Lewis StructuresPolarity◦Measure of uneven distribution of electrons

throughout a molecule

◦2 things to look for Asymmetry around central atom

Different elementsLone pairs

6.2 Lewis StructuresDetermine if polar or nonpolar

◦1. Br2

◦2. NH3

◦3. C2H6

◦4. CH3Cl

◦5. C2H4

◦6. H2O

6.2 Lewis Structures

Octet Exceptions◦B: BH3

◦I: IF3

◦Xe: XeF4

6.2 Lewis StructuresValence Shell Electron Pair Repulsion

(VSEPR) theory: Predicts shapes of covalent molecules using valence

electrons and bonds Electron pairs repel each other

Look at central atom (with most atoms attached) Count atoms attached and lone pairs (only on central atom)

6.3 Covalent FormulasLearning Targets:

Write names and formulas of covalent compounds.

6.3 Covalent FormulasMonoatomic◦Made of individual atoms

Diatomic◦Made of 2 atoms covalently bonded

7 elements always found in pairs when pure element Diatomic 7:

H2 , N2 , O2 , F2 , Cl2 , Br2 , I2

6.3 Covalent FormulasPrefixes

Prefix NumberMono- 1

Di- 2

Tri- 3

Tetra- 4

Penta- 5

Hexa- 6

Hepta- 7

Octa- 8

Nona- 9

Deca- 10

6.3 Covalent Formulas

Writing a formula from a name:◦Only nonmetals

1. In order of name, write symbols

2. Prefixes determine subscript (# of atoms) No prefix on 1st element 1 atom

6.3 Covalent FormulasYou try!1. Dihydrogen monosulfide

2. Carbon tetrahydride

3. Iodine pentafluoride

4. Hydrogen monochloride

5. Triphosphorous pentoxide

6.3 Covalent Formulas

Naming a covalent compound◦Only nonmetals

1. In order of formula, write name of each element.

2. Add prefixes in front to show amount If only 1 of first element, ignore “mono”

3. Change endings (all but first) to –”ide”

6.3 Covalent FormulasYou try!1. CO2

2. SeO

3. IF7

4. PH3

5. N2O5