Covalent

Bonding

Types of Bonding

Ionic Bonding occurs between metals and nonmetals.

Covalent Bonding occurs between two or more nonmetals.

Metallic Bonding occurs between metal atoms.

Molecular Compounds

Covalent bonds are the bonds formed between atoms who are sharing electrons.

A molecule is a neutral group of atoms joined together by covalent bonds.

A compound composed of molecules is a molecular compound.

Molecular formula is the chemical formula for a molecular compound. Examples: CO2 or NH3 See Pages

213 - 216

Molecular Compounds

Diatomic molecules are molecules that consist of two atoms. Example: N₂, O2, F₂, Cl₂, Br₂, I₂, H₂

Properties of Molecular Compounds

• Usually lower melting points than ionic compounds.

• Usually lower boiling points than ionic compounds.

See Page 214

Representing Molecules

Hydrocarbons

Molecular compounds that contain only carbon and hydrogen atoms.

H H H H H H H H H – C – C – C – C – C – C – C – C – H H H H H H H H H

Examples of Hydrocarbons Chains

Rings

Branches

Hydrocarbons

(Alkanes)

Methane CH₄ Ethane C₂H₆ Propane C₃H₈ Butane C₄H₁₀ Pentane C₅H₁₂ Hexane C₆H₁₄ Heptane C₇H₁₆ Octane C₈H₁₈ Nonane C₉H₂₀ Decane C₁₀H₂₂

General formula

for alkanes

CnH2n+2

Hydrocarbons

(Alkenes)

Methene CH2

Ethene C₂H4

Propene C₃H6

Butene C₄H8

Pentene C₅H10

Hexene C₆H12

Heptene C₇H14

Octene C₈H16

Nonene C₉H18

Decene C₁₀H20

General formula

for alkenes

CnH2n

Hydrocarbons

(Alkynes)

Ethyne C₂H2

Propyne C₃H4

Butyne C₄H6

Pentyne C₅H8

Hexyne C₆H10

Heptyne C₇H12

Octyne C₈H14

Nonyne C₉H16

Decyne C₁₀H18

General formula

for alkynes

CnH2n-2

Polymers • Molecules composed of a regularly

repeating structural sequence

• Extended chain structures are formed from simple molecules

Protein

Isomers Compounds that have the same formula but a different structure

Pentane, C5H12

glucose fructose galactose

Isomers

Naming Molecular Compounds (Other than hydrocarbons)

Prefixes Mono 1 Di 2 Tri 3 Tetra 4 Penta 5 Hexa 6 Hepta 7 Octa 8 Nona 9 Deca 10

Pg. 269

Rules for Naming Molecular Compounds

Name the elements in the molecule and indicate the number of each using the prefixes.

Ex. N2O5 dinitrogen pentaoxygen The suffix of the name of the second element is ‘-ide’. Ex. N2O5 dinitrogen pentaoxide

Rules for Naming Molecular Compounds

The vowel at the end of a prefix is dropped when the element begins with a vowel.

Ex. 1 oxygen would be monoxide not monooxide

If just one atom of the first element is in the formula, omit the prefix mono-.

Ex. CO2 would be carbon dioxide, not monocarbon dioxide

Write the name for each of the following:

1. P3Cl7

2. S3F4

3. N2Br6

4. N2O

5. C3H8

6. SF5

1. triphosphorus heptachloride

2. trisulfur tetrafluoride

3. dinitrogen hexabromide

4. dinitrogen monoxide

5. propane

6. sulfur pentafluoride

Due the following in your notes!

Due the following in your notes!

Write the formula for each of the following:

1. dihydrogen monoxide

2. trinitrogen pentasulfide

3. carbon dioxide

4. tetraphosphorus decaoxide

5. carbon tetrachloride

6. dinitrogen monoxide

1. H2O

2. N3S5

3. CO2

4. P4O10

5. CCl4

6. N2O

Empirical Formula

A formula with the lowest whole-

number ratio of elements in the

compound.

Molecular Formula

A chemical formula of a molecular

compound that shows the kinds and

numbers of atoms present in a

molecule of a compound.

Write the empirical formula for the following molecular formulas.

1. C6H14

2. N2O4

3. C4H8

4. C12H18O2

5. C12H22O11

1. C3H7

2. NO2

3. C2H4

4. C6H9O

5. C12H22O11

What are the only elements that exist in nature as uncombined atoms?

What term is used to describe such elements?

The noble gases.

Monatomic.

Which of the following gases in Earth’s

atmosphere would you expect to find as

molecules and which as individual

atoms?

a. nitrogen b. oxygen c. argon

d. chlorine e. helium f. hydrogen

Nitrogen, oxygen, chlorine, and

hydrogen would be molecules.

Argon and helium would be

individual atoms.

Homework

Write the names for the following: 1. N₂O₅ 2. P₃O₇ 3. S₃F₄ 4. CO₂ 5. N₂O₆ 6. N₂O 7. SO₃ 8. SF₆

Write the empirical formula for the following molecular formulas. 1. C₆H₁₄ 2. N₂O₄ 3. C₄H₈ 4. C₁₂H₁₈O₂ 5. N₄H₆O₄ 6. S₂O₇ 7. C₄H₃O₄ 8. C₁₂H₂₂O₁₁

Homework

Write the formulas for the following compounds: 1. dihydrogen tetraoxide 2. trinitrogen pentasulfide 3. carbon dioxide 4. tetraphosphorus decaoxide 5. dinitrogen monoxide 6. carbon tetrachloride

The Nature

of

Covalent

Bonding

Octet Rule

Atoms react by gaining or losing electrons so as to acquire the stable electron structure of a noble gas. (Atoms want to look like the noble gases, they want eight outermost electrons).

In order to obtain eight electrons, some atoms will share electrons with other atoms. When two atoms share two electrons (1 pair), it is called a single covalent bond.

See page 217

Unshared Electrons

Electrons that are not shared are called unshared pair electrons or lone pair electrons or nonbonding electrons.

See page 218

More Covalent Bonds

When two atoms share four electrons (two pairs), a double covalent bond is formed.

Double bonds are stronger and shorter than single bonds.

See pages 221-222

More Covalent Bonds

When two atoms share six electrons (3 pairs), a triple covalent bond is formed.

Triple bonds are stronger and shorter than double bonds and single bonds.

Polyatomic Ions

A polyatomic ion is a group of atoms that are covalently bonded, but has either a positive or negative charge. These ions behave as a unit.

See pages 223-225

Breaking the Bond

Bond dissociation energy is the energy required to break a covalent bond.

A strong bond (i.e. a triple bond) requires a large bond dissociation energy to break it.

See page 226

Resonance

Sometimes a molecule can have two or more legitimate Lewis structures due to the placement of single, double or triple bonds. This is known as resonance. If more than one structure is possible, then all structures must be drawn.

See page 227

Exceptions to the Octet Rule

Atoms that are happy with less than an octet: Be and B

Beryllium is happy with 4 electrons (2 pairs). Boron is happy with 6 electrons (3 pairs).

See pages 228-229

Exceptions to the Octet Rule

Some atoms are happy with more than an octet: P, S, I, Xe, Se, As

Some are happy with 10 electrons (5 pairs), others prefer 12 electrons (6 pairs).

See pages 228-229

List 3 ways in which the octet rule

can sometimes fail to be obeyed.

The octet rule cannot be satisfied in

molecules whose total number of

valence electrons is an odd number.

There are also molecules in which an

atom has fewer than a complete octet of

valence electrons.

There are also molecules in which an

atom has more than a complete octet.

Which of these compounds contain

elements that do not follow the octet

rule?

a. NF3 b. PCl2F3 c. SF4 d. SCl2

b and c do not follow the octet rule.

P and S atoms have 10 valence electrons.

Bonding

Theories

VSEPR Theory

Valence Shell Electron Pair Repulsion theory

VSEPR Theory

The repulsion between electron pairs causes molecular shapes to adjust so that the valence-electron pairs stay as far apart as possible.

The VSEPR theory plays a huge role in determining the polarity of molecules.

Chemquest 27 Molecular Shapes

See pages 232-233

VSEPR Theory

Some Molecular Shapes

Use VSEPR theory to predict the

shapes of the following species.

a. CO2 b. SiCl4 c. SO3

d. SCl2 e. CO f. H2Se

a. linear b. tetrahedral c. trigonal planar

d. bent e. linear f. bent

Predict the shape and bond angle

for the following:

a. CF4

b. PF3

c. F2O

d. BCl3

e. SiF4

a. tetrahedral, 109.5o

b. trigonal pyramidal, 107o (109.5o is acceptable)

c. bent, 104.5o

(109.5o is acceptable)

d. trigonal planar, 120o

e. tetrahedral, 109.5o

Molecular orbitals are produced when the atomic orbitals (s, p, d, f) of two atoms overlap.

A molecular orbital that can be occupied by two electrons of a covalent bond is called a bonding orbital.

When two atomic orbitals combine to form a molecular orbital that is symmetrical around the axis connecting two atomic nuclei, a sigma bond is formed.

Molecular Orbitals

Sigma Bonds

When two s orbitals combine, a sigma bond can form…

Sigma Bonds

…or when two p orbitals combine, a sigma bond can form.

When dealing with the p orbitals… after the sigma bond has been formed, the remaining p orbitals can form pi bonds.

Pi bonds

Pi bonds are weaker then sigma bonds because the orbitals creating the pi bonds do not overlap as much as the orbitals creating the sigma bond.

How are atomic and molecular

orbitals related?

When two atoms combine, their

atomic orbitals overlap to produce

molecular orbitals.

Hybrid Orbitals

Orbital hybridization provides information about both molecular bonding and molecular shape.

In hybridization, several atomic orbitals mix to form the same total number of equivalent hybrid orbitals.

5 types of hybridization: sp3, sp2, sp, dsp3, and d2sp3

Ex. 1s ___ 2s ___ 2p ___ ___ ___ 2s and 2p orbitals mix to give sp3. sp3 ___ ___ ___ ___

sp3 hybridization is based on the tetrahedral shape. If 4 electron regions are available around the atom, sp3 hybridization occurs.

2 H atoms 2 H atoms

1 C atom

When all 4 H atoms bond to the C atom, 4 sigma bonds form creating the methane molecule.

sp2 hybridization is based on the trigonal planar shape. If 3 electron regions are available around the atom, sp2 hybridization occurs.

2 H atoms 2 H atoms

1 C atom 1 C atom

When the sp2 orbitals overlap, a sigma bond forms. When the extra p orbital (in blue) overlaps,a pi bond forms. The s orbitals overlap with the outer sp2 orbitals and create sigma bonds.

sp hybridization is based on the linear shape. If only 2 electron regions are available around the atom, sp hybridization occurs.

Summary When determining hybridization, use Lewis structures to find the number of electron regions around the central atom(s).

If 4 electron regions are available around the central atom, sp3 hybridization will occur.

If 2 electron regions are available around the central atom, sp hybridization will occur.

If 3 electron regions are available around the central atom, sp2 hybridization will occur.

How are atomic and molecular orbitals

related?

When 2 atoms combine, their atomic orbitals overlap to produce molecular

orbitals.

What shape would you expect a simple carbon-containing compound to have if the carbon atom has the following hybridizations?

a. sp2 b. sp3 c. sp

a. trigonal planar b. tetrahedral c. linear

What types of hybrid orbitals are

involved in the bonding of the carbon

atoms in the following molecules?

a. CH4 b. H2C=CH2

c. HC≡CH d. N≡C-C≡N

a. sp3 b. sp2 c. sp d. sp

Indicate the hybrid orbitals used by each

carbon atom in the following compound.

H3C – C = C – C ≡ C – CH3

H H

sp3 sp3 sp sp sp2 sp2

Polar Bonds

and

Polar Molecules

Bond Polarity

Nonpolar covalent bonds are bonds where the bonding electrons are shared equally.

Polar covalent bonds are bonds where the bonding electrons are not shared equally.

See pages 237-238

Electronegativity

Electronegativity is the ability of an atom to attract electrons.

Electronegativity difference range

Most PROBABLE type of bond

0.0 to 0.4999 Nonpolar covalent

0.5 to 1.999 Polar covalent

Greater than or equal to 2.0

Ionic

Partial positive (δ⁺) charges and Partial negative (δ⁻) charges

H – F δ⁺ δ⁻

S – O δ⁺ δ⁻ 2.1 4.0

2.5 3.5

Polar Bonds

Dipole Moments

A molecule that has two poles is called a dipolar molecule or a dipole.

H – F

S – O

Polar Bonds

Polar / Nonpolar Molecules

To determine the polarity of the entire molecule, two factors must be taken into account: 1. The polarity of each bond that makes up the molecule. 2. The shape of the molecule.

1. Name the shape and give the approximate bond angle.

2. Describe what type of hybridization occurs with the central atom.

4. Is the molecule polar covalent or nonpolar covalent?

3. Are the bonds polar covalent or nonpolar covalent?

Network Solids

A solid substance that is entirely made up of covalently bonded atoms which build up to make a network. These are referred to as ‘giant molecules’.

Network solids typically have very high melting points (above 1000⁰C)

Examples include diamond (C), silicon carbide (SiC), silica (SiO₂)

What type of bond will form between

each pair of atoms – polar covalent,

nonpolar covalent, or ionic?

a. Na and O

b. P and O

c. Ba and Cl

d. O and O

e. N and Br

a. ionic

b. polar

c. ionic

d. nonpolar

e. polar

Draw structural formulas for each

molecule and identify polar covalent

bonds by assigning the partial positive

and partial negative symbols to the

appropriate atoms.

a. NH3 b. CCl4 c. H2O

State whether the following

compounds contain polar covalent,

nonpolar covalent, or ionic bonds,

based on their electronegativities.

a. KF

b. SO2

c. NO2

d. Cl2

a. ionic

b. polar covalent

c. polar covalent

d. nonpolar covalent