CHAPTER 12 – CHEMICAL BONDING - PowerPoint Presentation

Slide1

CHAPTER 12 – CHEMICAL BONDING

CHEMICAL BOND – A force that holds two or more atoms together as a unitIndividual atoms will naturally bond together to achieve a lower energy state (to be more stable)

3B-1 (of 42)

(9 –

34-42

+ 1-15

) (10 – 16-26

) (11- 27-42

+ 1-3

)Slide2

TYPES OF BONDS

Metal atoms easily lose electrons forming positive ions,

and nonmetal atoms easily gain electrons forming negative ions

1) METAL ATOMS AND NONMETAL ATOMS

3B-2

IONIC BOND – The electrostatic attraction between positive and negative ions

Ionic bonding forms giant crystalline

networks

containing billions of positive and negative ions that are strongly attracted together

Ionic bonding exists between metal and nonmetal ionsSlide3

+

Fe atoms

O atoms (molecules)

Fe

ions

and O

ions

Elemental Iron

Elemental Oxygen

Rust

3B-3Slide4

Nonmetal atoms attract each other’s valence electrons, and share the valence electrons between pairs of atoms

COVALENT BOND – The electrostatic attraction of shared electrons to the nuclei of bonding nonmetal atoms2) NONMETAL ATOMS

3B-4

Covalent bonding forms individual units called

molecules

, and while the atoms that covalently bond together strongly attract each other, the molecules that are created weakly attract each other

Covalent bonding exists between nonmetal atomsSlide5

3B-5

+

C atoms

Cl atoms (molecules)

CCl

4

molecules

Elemental Carbon

Elemental Chlorine

Carbon TetrachlorideSlide6

NONPOLAR COVALENT BOND – A bond in which 2 atoms are sharing electrons equally

POLAR COVALENT BOND – A bond in which 2 atoms are sharing electrons unequallyIONIC BOND – A bond in which two atoms have transferred electrons

Picture

3B-6Slide7

ELECTRONEGATIVITY – The attraction of an atom for shared electrons

The difference in the EN’s of 2 atoms tells the type of bond they make

Atom with the highest EN?F

Atom with the lowest EN?

Fr

EN Difference Bond

0.0

0.1 to 1.6

1.7

to 3.3

Nonpolar Covalent

Polar Covalent

Ionic

3B-7Slide8

N-N Bond

EN for N = 3.03.0 – 3.0 = 0.03B-8

 Nonpolar Covalent BondSlide9

Polar covalent bonds have partially positive and partially negative ends

DIPOLE MOMENT – The amount of separation of the positive and negative charges in a bond

C-O Bond

EN for C = 2.5, O = 3.5

3.5 – 2.5 =

1.0

H-S Bond

EN for H = 2.1, S = 2.5

2.5 – 2.1 = 0.4C –– Od+ d-

H –– Sd+ d-

DIPOLE MOMENT ARROW – Shows the direction of the dipole moment, pointing toward the negative end of the bond

C –– O

H –– S

3B-9

 Polar Covalent Bond

 Polar Covalent BondSlide10

Na-Cl Bond

EN for Na = 0.9, Cl = 3.03.0 – 0.9 = 2.1Na+ Cl

-

3B-10

 Ionic BondSlide11

+

BONDING IN IONIC COMPOUNDSAtoms form ions to obtain a stable, octet electron arrangement

Sodium chloride

Na

. .

.

Cl

: . .

A sodium chloride crystal is a symmetrical array of sodium and chloride ions in a 1:1 ratioEMPIRICAL FORMULA – The simplest whole number ratio of atoms of different elements in a compoundEmpirical Formula: NaCl

-

3B-11Slide12

+

Mg

2

. .

.

F

: . .

Magnesium fluoride

. .

.

F

:

. .

-

-

Empirical Formula: MgF

2

3B-12Slide13

K

Potassium nitride

K

+

+

+

K

.

.

N

:

.

-

3

Empirical Formula: K

3

N

3B-13Slide14

SIZES OF ATOMS AND IONS

Positive ions are smaller than their neutral atoms and negative ions are bigger than their neutral atoms

Na atom

Cl atom

Na

+

ion

Cl

-

ion

3B-14Slide15

1) The more energy levels an atom or ion has the larger it will be

2) With the same number of energy levels, the more protons an atom or ion has the smaller it will be

Li F Na Cl

Electrons

Energy Levels

Protons

Big to Small

3

2

33rd

9

2

9

4

th

11

3

11

1

st

17

3

17

2

nd

2

1

4

th

10

2

9

2

nd

10

2

11

3

rd

18

3

1

st

Li

+

F

-

Na

+

Cl

-

ISOELECTRONIC – Ions or atoms with the same number of electrons

Sizes of atoms or ions are determined by

3B-15Slide16

BONDING IN COVALENT MOLECULES

Atoms share electrons to obtain a stable, octet (or duet) arrangementsWater (H2O)

H

. .

.

O

: .

H

. .

H – O

:

H

←

LONE PAIR

← BONDING PAIR

LEWIS STRUCTURE – A diagram using electron dot notation to show how the valence electrons are arranged among bonded atoms

3B-16Slide17

To draw a proper Lewis Structure:

1 – Add up the valence e-s for all of the atoms in the molecule or ion

2 – Draw a skeletal structure by using pairs of electrons to make bonds

4 – If octets are not produced, make the atoms that have octets share more e

-

pairs with atoms that do not have octets

3 – Complete octets (or duets for H) for all atoms,

outer atoms first

, using the remaining valence e-s

3B-17Slide18

Cl S Cl

Sulfur dichloride, SCl2

6 + 7 + 7 = 20 valence e

-

s

3B-18Slide19

Phosphorus

tribromide, PBr3

5 + 7 + 7 + 7 = 26 valence e-s

Br P Br

Br

3B-19Slide20

Ammonia, NH

3

5 + 1 + 1 + 1 = 8 valence e-s

H N H

H

3B-20Slide21

Methane, CH

4

4 + 1 + 1 + 1 + 1 = 8 valence e-s

H

H C H

H

3B-21Slide22

Fluorine, F

2

7 + 7 = 14 valence e-s

F F

SINGLE BOND – One shared pair of e

-

s between two atoms

3B-22Slide23

Oxygen, O

2

6 + 6 = 12 valence e-s

O O

DOUBLE BOND – Two shared pairs of e

-

s between two atoms

3B-23Slide24

Nitrogen, N

2

5 + 5 = 10 valence e-s

N N

TRIPLE BOND – Three shared pairs of e

-

s between two atoms

3B-24Slide25

Hydrogen cyanide, HCN

1 + 4 + 5 = 10 valence e

-s

H C N

Carbon disulfide, CS

2

4 + 6 + 6 = 16 valence e

-

s

S C S

3B-25Slide26

O

O S OOSulfate, SO42-

6 + 4(6)

+ 2 = 32 valence e

-

s

2-

Ammonium, NH

4

+

H

H N H

H

5 + 4(1)

- 1 = 8 valence e

-

s

+

3B-26Slide27

O

O OO O O

Ozone, O3

6 + 6 + 6 = 18 valence e

-

s

O

O

O

or

O

O

O

↔

RESONANCE – When more than one Lewis structure can be drawn for a molecule or ion

RESONANCE STRUCTURES – The Lewis structures that can be drawn for the molecule or ion

The real ozone molecule is an average of its resonance structures

3B-27Slide28

O

O OO O O

O

O

O

↔

2 “1½” bonds

3B-28Slide29

MOLECULAR SHAPE

VSEPR THEORY (Valence Shell Electron Pair Repulsion) – All atoms and lone pairs attached to a central atom will spread out as far as possible to minimize repulsionA Lewis structure must be drawn to use the VSEPR Theory

3B-29Slide30

H

H C HH

STERIC NUMBER (SN) – The sum of the bonded atoms and lone pairs on a central atomThe steric number of carbon is 4 (SN = 4): 4 bonded atoms and no lone pairs

Tetrahedral

Bond angle is 109.5

°

H

C

H

H

H

3B-30Slide31

H N H

H

The steric number of nitrogen is 4 (SN = 4):

3 bonded atoms and 1 lone pairs

Trigonal Pyramidal

Bond angle is 108

°

N

H

H

H

3B-31Slide32

The steric number of oxygen is 4 (SN = 4):

2 bonded atoms and 2 lone pairsBentBond angle is 105

°

O

H

H

H O

H

3B-32Slide33

Formaldehyde, H

2CO

1 + 1 + 4 + 6

H

H C O

= 12 valence e

-

s

The steric number of carbon is 3 (SN = 3):

3 bonded atoms and 0 lone pairs

Trigonal

Planar

Bond

angle is 120

°

O

H

H

C

3B-33Slide34

SiS

2

4 + 6 + 6

S Si S

= 16 valence e

-

s

The steric number of silicon is 2 (SN = 2):

2 bonded atoms and 0 lone pairs

Linear

Bond angle is 180

°

S Si S

3B-34Slide35

SN

444332

Atoms 4

3

2

3

2 2

Shape Tetrahedral Trigonal Pyramidal Bent (109.5°) Trigonal Planar Bent (120°) Linear

3B-35

Lone

Pairs

0

1

2

0

1

0 Slide36

MOLECULAR POLARITY

A BOND is polar if it has a positive end and a negative endA MOLECULE is polar if it has a positive end and a negative end3B-36

To determine if a molecule is polar or nonpolar:

1) Draw the correct Lewis structure

Draw its correct shape

Use EN’s to determine if the

BONDS

in the molecule are polar or nonpolarFor the polar bonds, label the positive and negative ends with δ+ and δ-If a line can be drawn separating all δ+’s from all δ

-’s, the molecule is polar, if not its nonpolarSlide37

. .H O : H

O

H

H

δ

+

δ

-

δ

+

δ

-

EN’s: O = 3.5, H = 2.1

3.5 – 2.1 = 1.4



the O-H

BONDS

are polar

All of the

δ

+

’s can be separated from all of the

δ

-

’s, 

the H

2

O

MOLECULE

is polar

3B-37Slide38

N

δ

+

δ

-

δ

+

δ

-

EN’s: N = 3.0, H = 2.1

3.0 – 2.1 = 0.9



the N-H

BONDS

are polar

All of the

δ

+

’s can be separated from all of the

δ

-

’s, 

the NH

3

MOLECULE

is polar

H N H

H

H

H

H

δ

+

δ

-

3B-38Slide39

F

C F

F

F

δ

+

F

F C F

F

Carbon tetrafluoride, CF

4

4 + 4(7)

= 32 valence e

-

s

EN’s: C = 2.5, F = 4.0

4.0 – 2.5 = 1.5



the C-F

BONDS

are polar

All of the

δ

+

’s cannot be separated from all of the

δ

-

’s, 

the CF

4

MOLECULE

is nonpolar

δ

+

δ

-

δ

-

δ

-

δ

+

δ

-

δ

+

3B-39Slide40

REVIEW FOR TEST

Electromagnetic Radiation, PhotonsGround State, Excited StateOrbitalEnergy Levels (Sublevels and Number of Orbitals They Contain)Sublevels (Shape, Number, and Starting Energy Level)Orbital Notation

Electron Configuration NotationElectron Dot Notation

2B-40Slide41

REVIEW FOR TEST

Valence ElectronsOctetElectron PairPeriodic Trends in

Metal, Nonmetal Activity Atomic Radii Ionization Energy (and Write Equation) Electron Affinity (and Write Equation)

2B-41Slide42

REVIEW FOR TEST

Ionic Bonds, Covalent Bonds Electronegativity and its Periodic TrendBond Polarity from Electronegativities

Ion SizesLewis Structures for Ionic Compounds and Covalent CompoundsResonance Molecular ShapesMolecular Polarity

2B-42