Covalent Bonding

Outline•Introduction: Multiple bonds, Bond strength

•Naming molecules

•Drawing Lewis Structures

•Molecular shapes and VSEPR theory•Bond Polarity

Why do atoms bond?

•Recall that noble gases do not form compounds.

•This is because their electron arrangements, which consists of a full outer energy level, are stable.

Why do atoms bond?

•Recall that metal atoms and non-metal atoms can gain stability by transferring (gaining or losing) electrons to form ions.

•Atoms can also share valence electrons to acquire the stable electron configuration of noble gases.

Covalent Bonding

•A covalent bond is the chemical bond that results from sharing valence electrons.•Compounds made up of covalent bonding are called molecules.•Covalent bonding generally occurs between non-metals, that are near each other in the periodic table.

Covalent Bonding

•Diatomic molecules: Eg. Hydrogen, fluorine, oxygen.

•Bonding and nonbonding pairs:

Covalent Bonding

•Lewis Structures: Show arrangement of electrons in a molecule.

•A line represents a single covalent bond in a Lewis structure.

•Eg.

Covalent Bonding

•Single bonds: Groups 17, 16, 15, 14

•Textbook p.244 Q1-6

Covalent Bonding

•Single bonds are also called sigma bonds.

•Multiple Covalent Bonds: •Double: two pairs of electrons are sharedeg. Oxygen O2 molecule•Double covalent bonds are made of one sigma bond and one pi bond.

Covalent Bonding

•Multiple Covalent Bonds:

•Triple: three pairs of electrons are sharedeg. Nitrogen N2 molecule

•Triple covalent bonds are made of one sigma bond and two pi bonds.

Covalent Bonding

•Strength of covalent bonds:

•Depends on the distance between the bonded nuclei.

•The distance between the two bonded nuclei at the position of maximum attraction is called the bond length.

Covalent Bonding

•Strength of covalent bonds:

•More shared pairs = shorter bond length, stronger bond.

Covalent Bonding

Molecule Bond Type Bond Length Bond-Dissociation Energy

F2 Single 1.43 x 10-10 m 159 kJ/mol

O2 Double 1.21 x 10-10 m 498 kJ/mol

N2 Triple 1.10 x 10-10 m 945 kJ/mol

Naming Molecules

•Binary Molecular Compounds: (2 nonmetals)

•1. First element in the formula is named first, using entire name.

•2. Second element has suffix –ide

•3. Prefixes are used to indicate the number of atoms in the compound.

Naming Molecules

•Common prefixes: p.248Number of Atoms

Prefix Number of Atoms

Prefix

1 mono 6 hexa

2 di 7 hepta

3 tri 8 octa

4 tetra 9 nona

5 penta 10 deca

Naming Molecules

•Binary Molecular Compounds: (2 nonmetals)

•Exceptions:

•First element in the compound name does not use mono.

•Prefix that ends up with consecutive vowels: drop one vowel.

•P. 249 Q14-18

Naming Molecules

•Acids:

• If a compound produces hydrogen ions in solution, it is called an acid.

•Common acids:

•Write “hydro-” prefix in front of the first word.

•HX (X is a halogen) are all acids.

Naming Molecules

•Common acids:

•Oxyacids(acid containing a hydrogen atom and an oxyanion).•ClO3

- : Chlorate ion HClO3 : chloric acid•ClO2

- : Chlorite ion HClO2: chlorous acid

•NO3- : Nitrate ion HNO3: Nitric acid

•NO2- : Nitrite ion HNO2: Nitrous acid

Naming Molecules

•Common acids:

•Oxyacids(acid containing a hydrogen atom and an oxyanion).CO3

2-: carbonate ion H2CO3: carbonic acid

•SO42- :sulfate ion H2SO4 : sulfuric acid

•S2- : sulfide ion H2S : hydrosulfuric acid

•P. 251 Q19-30