Chapter 15/16Bonding

Types of Chemical Bonds

A. Ionic bond: Results from the electrostatic

attraction between positive and negative ions

B. Covalent bond: Resulting from the sharing of

electrons

A+ : B-

1. A + B

A : B

2. Chemical bonds between unlike atoms are never really ionic

or covalent, fall somewhere in between

3. How do we determine whether a bond is ionic or covalent?

a. Compare electronegativities

(ability of an atom to attract electrons)

b. Electronegativity difference

4.% ionic character

100% 50% 5% 0%

4.0 1.7 0.3 0. 0

ionic Polar covalent Nonpolar

covalent

5. Nonpolar covalent:

a. share electrons equally

b. No charge

6. Polar covalent:

a. share electrons unequally

b. Have a partial positive (δ+) and a partial negative charge (δ-)

7. Examples:

Using the following chart classify bonds between the following,

which bond will be more negative?

Element EN value

Sulfur 2.5

Hydrogen 2.1

Cesium 0.7

Chlorine 2.5

a) H-S b) Ce-S c) S-Cl

C.Metallic bonding

1. happens with solids and liquids

2. metal atoms give electrons

3. electrons slide through the material (not transferred to a negative)

Covalent bonding and molecular compounds

1. Share electrons

2. Still using valance electrons

3. Share 1 pair of electrons: a single bond

4. Two shared pairs: a double bond

5. Three shared pairs: a triple bond

6. Examples:

a) H2 H +H = H:H

H-H

b. O2

c. N2

7. Octet rule: Chemical compounds tend to form so that each

atom, by gaining, losing, or sharing electrons, has an octet

of electrons in its highest occupied energy level

a. He is happy with 2 electrons

b. exceptions to the octet rule

Structures

1. Molecular structure: shows the types and numbers of atoms

PH3

2. Lewis structure:

a. Atomic symbols represent nuclei and inner-shell electrons

b. Dot-pairs or dashes between two atomic symbols

c. Will have shared pairs and unshared pairs

ex. Cl-Cl

3. Structural formula

a. Indicates the kind, number, arrangement, and bonds of

the atoms in a molecule

b. H-P-H

H

4.Examples:

a. Draw the Lewis structure of iodemethane (CH3I)

b. Ammonia (NH3)

4 Step Method 1. Add total valence e-

2. Draw skeleton structure

3. Subtract bonded e- from total valence e-

4. Distribute remaining e- (in pairs) to satisfy octet rule

Examples:

SO2

NO3-

• Resonance

1. Refers to bonding in molecules that cannot be correctly represented

by a single Lewis structure

2. SO3

Ionic bonding and Ionic Compounds

1. Electron-dot structure

a. NaCl

b. CaF2

3. PCl3

*4. AlCl3

2. Lattice: The energy released when one mole of an ionic crystalline compound is formed

from gaseous ions.

Metallic Bonding

1. metallic bond: resulting from the attraction between

positive ions and surrounding mobile electrons

The VSEPR Theory

(Valence-Shell Electron Pair Repulsion Theory)

The pairs of electrons in the valence shell will repel each other until they are as far away from other electron pairs as they can be.

Molecular Atoms bonded Lone pairs Type Formula Formula

Shape to central atom of electrons of molecule example Structure

around central

atom

Linear NA NA AB HCl H – Cl

Linear 2 0 AB2 CO2 O = C = O

Bent 2 1 or 2 AB2E H2O O

H H

Trigonal 3 0 AB3 AlCl3 Cl

Planar Al

Cl Cl

Trigonal 3 1 AB3E NH3 N

Pyramidal H H H

Molecular Atoms bonded Lone pairs Type Formula Formula

Shape to central atom of electrons of molecule example Structure

around central

atom

Tetrahedral 4 0 AB4 CH4 H

C

H H

H

E: stands for unshared electron pair

***Make sure you put dots around the elements where they needed them.

2. How do we use this table?

A. Draw the shape of PCl3.

(Is it eitherAB3 or AB3E)

B. CS2 Is it AB2 or AB2E

To move or not to move: 1. Polarity a. Nonpolar molecules

1. electrons shared equally

2. molecule doesn’t move

b. Polar molecules 1. electrons shared unequally

2. molecule would move in the direction of

strongest pull

2. CF4

3. CSO

Hybridization

1. The blending of two or more orbitals to make a new

orbital with a new shape

2. Helps explain the bonding and geometry of some Group

15 and Group 16 elements

3. Hybridization rules

How to find the (-) areas:

a. each bond type counts as 1 area of – charge

b. Each unshared pair of electrons count

c. NEVER COUNT HYDROGEN

d. areas of hybridization

(-) charge types

2 sp

3 sp2

4 sp3

e. Examples

1. CH4

2. NH3

3. CO2

4. NOF

Bond length

A. The average distance between two bonded atoms, minimum potential energy

1. Longest - single bonds

2. Middle - double bonds

3. Shortest - triple bonds

B. Bond energy

1. Energy required to break a chemical bond and form

neutral atoms

2. can be related to bond length

a. Long bond length needs low energy to break it apart

b. Short bond length will need high energy

3. chart

bond Bond length Bond energy

H-H 74 436

C-H 110 414

N-H 98 389

N-N 140 159

Other properties of polarity

1. Boiling point a. Temp at which a liquid turns to a

gas

b. The greater attraction of charges, the higher the boiling point

c. Ionic - highest

NaCl + -

- +

d. Polar covalent - middle

&+ &-

&- &+

e. Nonpolar covalent - lowest

2. Intermolecular forces

a. Dipole-dipole

1. Polar molecules

2. The attraction between the + pole of one molecule

and the - pole of a different molecule

3. Has a middle boiling point

b. London dispersion force 1. Nonpolar 2. The attraction between the

temporary pole of one molecule with an adjacent molecule

3. Low boiling point

c. hydrogen bonding

1. attraction between a hydrogen atom and an unshared pair of electrons on a strongly electronegative atom (fluorine, oxygen, nitrogen

2. EN difference between hydrogen and fluorine makes them highly polar

3. highest boiling points

Melting points/freezing points

A. ionic bonds

1. Strongest attraction

2. Highest melting/freezing point

B. Polar bonds

1. Somewhat strong bonds

2. Middle values

C. Nonpolar bonds

1. Weakest attractions

2. Lowest melting/freezing points

D. Ex. Rank from lowest to highest

1) boiling point

2) freezing /melting points

H2O NaCl F2

Quiz Q’s

1.Draw the correct shape of compound.

2.Name the shape.

3.What are the bond angles?

4.What is the hybridization?

5.What type of molecule is it (polar or nonpolar)?

BCl3