Unit 04

Chemical Bonding

Valence e-

– Valence e- - e- in the highest occupied energy level of an element’s atom

– Same as group # for groups 1 & 2– Subtract 10 from groups 13-18

• electrons used in chemical bonding

Lewis Dot Structure – shows number of valence e-

Ex: bromine

Br● ●

●●●

● ●

Valence e-

White Board Practice

K C

O Ar

● ●

●

●

●

●

●

●

●

●

●

● ●

●●

●●

●●

Learning Check

Which Lewis Dot Structure is incorrect?A.

Mg B

S Xe

● ●

●

●

●

●

●

●

●

●

●

● ●

●●

●●

●●

●

B. D.

C.

Octet Rule:

- when forming compounds atoms want to have 8 e- (s2p6) like the noble gases (except He)

Na (atom)

1s22s22p63s1

●

lose 1 e-

Na (cation)

+1s22s22p6

octetUsing the Dot Structure

Na (neutral

atom)

Na (cation)

lose 1 e- +

●

Mg (neutral

atom)

Mg (cation)

lose 2 e-2+

●

Cations (metals): positively charged ion, tend to lose e-

●

B

(neutral atom)

B (cation)

lose 3 e- +3●

●

Cations ca+ion

+1

+2 +3

gain 2e-

Cl

(neutral atom)

O (neutral

atom)

Cl (atom)

1s22s22p63s23p5

●

gain 1 e-

Cl (chloride ion)

-1s22s22p63s23p6

octetUsing the Dot Structure

Cl

(chloride ion)

-

●

O

(oxide ion)

2-●

●●

●

● ●

●gain 1e-

●

●●●

●

●●

●●

●

valence

● ●

●●●

● ●

●

●

●

Anions (Nonmetals) – negatively charged ions, gain e-

gain 3e- N

(neutral atom)

●

N

Nitride ion)

●●

●●

●

●●

●●

●●

●

-3

-2

Anions

-1-3

White Board Practice

N

I

Li

Ca

●

●

●

●

●

N

(nitride ion)

3-gain 3e-

●

●●

●●●

●

●

●

●

●

●

●

●●

I

(chloride ion)

gain e-

●

●●

●●

●●

●

-

●

LiLose 1 e- +

CaLose 2e- +2

●

●

Ionic Compound:

1. ionic compounds form crystals2. high melting and boiling points3. hard and brittle4. conduct electricity when dissolved in water

or melted

Properties

•Composed of a metal (cation) and nonmetal (anion)•Ionic bond – oppositely charged ions attract•Electrically neutral (+) = (-)•Generally called salts

Ionic Bonding

Na Cl

1. Sodium and Chlorine

●● ●

●●

●

●

●

donates e-

Na+ ● Cl●

●●

●

●

●

●

2. Potassium and Oxygen

K O● ●

●

●

●●

donates e -

K+● O

●●●

●●

●

●

●

+

+

K●

donates e-

K+

-2

+1 -2

-

K2O

NaCl

+1 -1

Does O have 8?

Al

3. Aluminum and Bromine

Mg N●

●●

●●

Mg+2● N

●●●

●●

●

●●

+● Mg+2

-3

● ●●●

●●

●

●

Al+3

● Br●

●●

●

●

●

●

+

●

●

Br● ●

●●

●●

●Br

● ●●●

●●

●Br

+3 -1

● Br●

●●

●

●

●

●

● Br●

●●

●

●

●

●

-

-

-+2 -3

Mg

4. Magnesium and Nitrogen

Mg●

●

●

●

N●

●

●●

●

Mg+2● N

●●●

●●

●

● -3

AlBr3

Mg3N2

Does Al have moreelectrons?

Does N have 8 yet?

What about Mg’s other e-?

Does N have 8 yet?

Ionic Bonding– Title left side of spiral Ionic Bonding– Copy the problem– Draw the Lewis Structure for ea. element used in

bonding– CATION = RED– ANION = BLUE/GREENISH– Show donated e- with an arrow– Show New ions charges– Put a BOX around the Formula

EXAMPLE:

1. Potassium & Fluorine

K●

F● ●

●●

●●+ ● K + F● ●

●●

●●●●

KF

-

Bonding in Metals

• Metallic bonds – the attraction between positive ions and surrounding mobile electrons

Sea of ElectronsMetal cations

• Good conductors of electrical current, ductile (wires), malleable (forced into shapes)

Covalent Compounds

• Also called MOLECULAR COMPOUNDS• Formed from 2 or more nonmetals

• Low melting and boiling point

CharacteristicCovalent compoundMolecular compound

Ionic compound

Representative unit MoleculeFormula unit (balance

of oppositely charged ions)

Type of elements Nonmetallic Metallic combined with nonmetallic

Melting & Boiling point

Low High

Important differences between covalent and ionic compounds

Covalent Bonds– Forms when 2 atoms share a pair of valence e-

Types of Covalent Bonds1. Single Covalent Bond – two atoms share a pair of e-

Ex: F2

F F● ●

●●

●●

● ●●●●

●● ●F F● ●

●●

●●

● ●●●●

●● ●and F F

● ●●●

●

●●●●

●● ●

Unshared pair – e- not shared between atoms

What makes this bonding work?Atoms have 8 e- in their outer level to make them stable

Ex: H2

H● H● H H

Why does H2 only need 2 e- to be stable?first energy level only contains 2 e-

Covalent Bonds

2. Double Covalent Bond – 2 pairs of e- are shared between atomsEx: O2

O●●

●●●

●●O

●●●●●

●O● ●

● O and●●●

● ● ●

● ●O● ● O

● ●

● ●●

●

Covalent Bonds

3. Triple Covalent Bond – 3 pairs of e- are shared between atomsEx: N2

NN●●

●●

●N●●

●●

●N●

● N●● and N●

●●●● ●● ●● ●

Covalent Bonds

Covalent Lewis Dot Structures

1. Draw each atom’s Lewis Structure2. Connect single electrons until each atom has 8 e- (H

only 2)3. The central atom is often the first atom written & is

usually the atom w/the least # of e-. (Exception – H can’t be the central atom)

4. Place the unshared pairs around the atoms so ea. is stable (8 around it, except H – only 2)

Examples:1. Br2

Br● ●

● ●●

●

●Br● ●

●●

●

●

●Br● ●

●●

●

●Br● ●

●

●●

●

Covalent Lewis Dot Structures

2. NH3

N●

● ●

●

●

H●

H●

H●

N● ●

HH

H

3. CO2

C●

●

●

●

O

O● ●

● ●●●

●●●

●

●●

CO O● ●

●●

● ●

●●

4. CCl4

C ●

●

●

Cl●

Cl●

Cl●C ClCl

Cl

5. H2O

H●

O● ●●

●●

●

●

Cl

● ●

● ●● ●

● ●

● ●● ●

● ●

●●

●●

●●

●●●

● ●

Cl● ●

● ●● ●

●●

● ●

● ●

●●

● ●

●●

●●

●●

●●

H●

O

H

H● ● ●

●

White Board Practice Problems:

1. CH4

C●

●

●

●

H●

H●

H●

H●

C H

H

HH

2. H2

White Board Practice Problems:

H HHH● ●

3. PH3

White Board Practice Problems:

P ●

● ●

●

●

H●

H●

H●

P● ●

HH

H

4. OF2

White Board Practice Problems:

O● ●●

●●●

F●

F

● ●

● ●● ●

● ●

●●

●●●

O● ●

● ● F● ●

● ●

●●F● ●

●●

● ●

5. CHI3

White Board Practice Problems:

C●

●

●

●

H●

I●

I

● ●

● ●● ●

● ●●

●●

●●

I●

● ●

● ●

●● C I

II

●●

H● ●● ●

●●

● ●

● ●● ●

●●

●●

Title Left Side: Covalent Bonding Practice

Draw the molecule then tell me how many double bonds does it have?

1. CO2

Draw the molecule then tell me what kind of covalent bond is formed.

2. P2

Draw the following molecules.3. SiO2

4. CH4

VSEPR Theory

• Explains the shapes of molecules. • The VSEPR theory states: b/c electrons repel each

other, molecules adjust their shapes so that the valence e- pairs are as far apart from each other as possible.

• These are called electrostatic balanced positions

Shape Formula Bond Angle ElectronsLinear AX2 180o 4 shared

0 unshared

Linear AX 180o 1 shared3 unshared

Bent AX2 105o 2 shared2 unshared

Trigonal Pyramidal

AX3 107o 3 shared1 unshared

Tetrahedral AX4 109.5o 4 shared0 unshared

Trigonal Planar AX3 120o 4 shared0 unshared

Contains a double bond

Bond Polarity

Polar Covalent Bond – when 2 atoms are joined by a covalent bond and the bonding electrons are not shared equally

Nonpolar Covalent Bond – when 2 atoms are joined by a covalent bond and the bonding electrons are shared equally

Bond Polarity

Differences between polar, nonpolar, and ionic bonds

How do you determine if a bond is polar, nonpolar, or ionic?

Subtract the electronegativities of the bonding atoms (p. 265 in textbook)

Electronegativity Differences & Bond Type

Type of BondElectronegativity Difference Range

Nonpolar Covalent Bond 0.0 – 0.4

Polar Covalent Bond 0.5 – 1.67

Ionic Bond greater than 1.67

Determine if the bonds between the following atoms are polar, nonpolar, or ionic:

H 2.2C 2.55 0.35 Nonpolar

1. Hydrogen and Carbon

2. Oxygen and Carbon

3. Potassium and Chlorine

4. Fluorine and Fluorine

O 3.44C 2.55 0.89 Polar

K 0.82Cl 3.16 2.34 Ionic

F 3.98F 3.98 0.0 Nonpolar

Polar Molecule – a molecule with a positive and negative end. Polar bonds must be present.

• Take into account if the molecule is symmetrical and if polar bonds are present.

Polarity of Molecule

Polarity of Molecule

It is possible to have polar bonds but not a polar molecule!• Carbon dioxide has 2 polar bonds and is linear (symmetrical).• Bond polarities cancel out b/c they are in opposite directions.

CarbonOxygen Oxygen

Draw the dot structure of the following molecules – then predict the shape and polarity

1. I2

2. H2S

3. CHCl3

4. CO2