chapter 13: phenomena

Chapter 13: Bonding: General Concepts

Chapter 13: Phenomena

Phenomena: Scientists measured the bond angles of some common molecules.

In the pictures below each line represents a bond that contains 2 electrons. If

multiple lines are drawn together these are double or triple bonds and contain 4

and 6 electrons respectively. What patterns do you notice from the data?

H HN

H

H HN

H

H +

O

CO

O

CN H

Cl ClC

Cl

Cl

B

F

Bond Angles: 107˚

Bond Angles: 109.5˚ Bond Angles: 109.5˚

Bond Angles: 120˚

C

O

Bond Angles: 105˚

Bond Angles: 119˚

Bond Angles: 120˚ Bond Angle: 117˚

Bond Angles: 180˚

Bond Angles: 180˚

a) b) c)

d)

g)

e)

h)

f)

i)

j)

S

O

Chapter 13

Bonding:

General Concepts

o Types of Bonding

o Electronegativity

o Lewis Structures

o Strength/Length of

Covalent Bonds

o Shapes of Molecules

(VSEPR)

o Polar Molecules

2

Big Idea: Bonds are formed

from the attraction

between oppositely

charged ions or by

sharing electrons.

Only the valence

electrons participate

in bonding. The shape

of the molecules

maximize the distance

between areas of high

electron density.


Lewis Structure Review

Drawing Lewis Structures that Obey the Octet Rule

Step 3: Determine number of bonds

# 𝑏𝑜𝑛𝑑𝑠 =𝑤𝑎𝑛𝑡𝑒𝑑−𝑣𝑎𝑙𝑒𝑛𝑐𝑒

2

Step 4: Determine number of electrons

# 𝑒− = 𝑣𝑎𝑙𝑒𝑛𝑐𝑒 − 2 𝑏𝑜𝑛𝑑𝑠

3

CO32- 1(C) 3(O) 2(e-) Total

Step 1:

(Determine

Valence e-)

Step 2:

(Determine

Wanted e-)



Resonance: A blend of Lewis structures into a

single composite hybrid structure.

Formal Charge = Valence e- – e- Surrounding Atom

4

O

O

O C

2-O

OO C O

O

OC

2- 2-

Note: Loan pairs count for 2 e- and bonds count for 1 e-.

O

O

O C

2-



Drawing Lewis Structures that Minimize Formal Charges (Only atoms in period 3 and later can

expand their octets)

Step 2: Find structure with lowest formal charges

5

SO2 1(S) 2(O) Total

Step 1:

(Determine

Valence e-)


Shapes of Molecules (VSEPR)

VSEPR (Valence-Shell Electron-Pair Repulsion Model):

Extends Lewis’s theory of bonding to account for

molecular shapes by adding rules that account for

bond angle.

Rule 1: Regions of high electron concentration

(bonds and lone pairs on the central atom) repel

one another and to minimize their repulsion,

these regions move as far apart as possible while

maintaining the same distance from the central

atom.

Rule 2: There is no distinction between single and

multiple bonds: a multiple bond is treated as a

single region of high electron concentration.

6



Rule 3: All regions of high electron density, lone

pairs and bonds, are included in a description of

the electronic arrangement, but only the

positions of atoms are considered when

reporting the shape of a molecule (molecular

shape).

Rule 4: The strengths of repulsion are in the order

lone pair – lone pair > lone pair – atom > atom –

atom.

7



Assigning Shape and Bond Angles of Molecules

Step 1: Draw the Lewis structure.

Step 2: Assign the electronic arrangement

around the central atom (linear, trigonal planer,

tetrahedral)

Step 3: Identify the molecular shape (linear,

bent, trigonal planer, trigonal pyramidal,

tetrahedral)

Step 4: Figure out the bond angle (allow for

distortion)

8

Note: Electronic arrangement includes all areas of electron density

(lone pairs and bonds).

Note: Molecular shape includes only bonds.



Possible Electronic Arrangements

9



Possible Molecular Arrangements

The names of the shapes of simple molecules and their bond angles. Lone pairs of electrons are not shown.

10



11

No Lone PairsTetrahedral

1 Lone PairTrigonal Pyramidal

2 Lone PairsBent

No Lone PairsTrigonal Planar

1 Lone PairBent

No Lone PairsLinear

3 Areas of

Electron

Density

2 Areas of

Electron

Density

4 Areas

of

Electron

Density



12

No Lone Pairs

Trigonal

Bipyramidal

2 Lone

Pairs

T-Shaped

3 Lone

Pair

Linear

1 Lone

Pair

Seesaw

5 Areas of

Electron Density



13

No Lone

Pairs

Octahedral

1 Lone Pair

Square

Pyramidal

3 Lone

Pairs

T-Shaped

4 Lone Pair

Linear

2 Lone Pairs

Square Planer

6 Areas of Electron

Density



Step 1: Draw Lewis Structure

Determine number of bonds


2

Determine number of electrons


Step 2: Determine Electronic Shape

Step 3: Determine Molecular Shape

Step 4: Determine Angle

14

CH4 1(C) 4(H) Total

Valence e-

Wanted e-



Step 1: Draw Lewis Structure (Obeys Octet Rule)

Determine number of bonds


2

Determine number of electrons


Step 2: Determine Electronic Shape

Step 3: Determine Molecular Shape

Step 4: Determine Angle

15

SO32- 1(S) 3(O) 2(e-) Total

Valence e-

Wanted e-


Student Question


What is the most likely shape of ICl4-?

Helpful Hint: Make sure that your formal

charges are minimized.

a) Octahedral

b) Trigonal Planar

c) Seesaw

d) Tetrahedral

e) None of the Above

16


Student Question

Polar Molecules

Is PCl4- polar or nonpolar?

Helpful Hint: Make sure that your formal

charges are minimized.

a) Polar

b) Nonpolar

17


Take Away From Chapter 13

Big Idea: Bonds are formed from the attraction

between oppositely charged ions or by sharing

electrons. Only the valence electrons participate in

bonding. The shape of the molecules maximize the

distance between areas of high electron density.

Lewis Structures

Be able to draw Lewis structures of covalent

compounds. (57,58)

Know how to calculate formal charges.(78,79)

Identification of most likely Lewis structure.

Know when multiple resonance structures are possible for a

compound.(60,61,65,73)

Know when atoms can expand their octets (group 3 and

greater).(80)

18

Numbers correspond to end of chapter questions.


Take Away From Chapter 13

Shape of Molecules (VSEPR) (88,91)

Know how to determine electronic shape.

Linear, trigonal planar, tetrahedral, trigonal bipyramidal, or

octahedral.

Know how to determine molecular shape.

Linear, angular, trigonal planar, trigonal pyramidal, T-

shaped, tetrahedral, seesaw, square planar, trigonal

bipyramidal, square pyramidal, or octahedral.

Know how to determine bond angles.

Polar Molecules

Be able to determine if a molecule is polar or non polar.

(93,94)

19

Numbers correspond to end of chapter questions.

chapter 13: phenomena

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