1 when atoms meet. 2 bonding forces electron – electron repulsive forces nucleus – nucleus...

38
1 When Atoms Meet

Upload: ashley-weaver

Post on 16-Dec-2015

222 views

Category:

Documents


1 download

TRANSCRIPT

Page 1: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

1

When Atoms Meet

Page 2: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

2

Bonding Forces

Electron – electron repulsive forces

Nucleus – nucleus repulsive forces

Electron – necleus attractive forces

Bonds Forces that hold groups of atoms

together and make them function

as a unit.

Page 3: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

3

Metals and Nonmetals

Page 4: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

4

Types of Chemical Bonding

1. Metal with nonmetal:

electron transfer and ionic bonding

Page 5: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

5

Three models of chemical bonding

Electron transfer

Ionic

Page 6: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

6

Types of Chemical Bonding

1. Metal with nonmetal:

electron transfer and ionic bonding

2. Nonmetal with nonmetal:

electron sharing and covalent bonding

Page 7: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

7

Three models of chemical bonding

Electron transfer Electron sharing

Ionic Covalent

Page 8: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

8

Types of Chemical Bonding

1. Metal with nonmetal:

electron transfer and ionic bonding

2. Nonmetal with nonmetal:

electron sharing and covalent bonding

3. Metal with metal:

electron pooling and metallic bonding

Page 9: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

9

Three models of chemical bonding

Electron transfer Electron sharing Electron pooling

Ionic Covalent Metallic

Page 10: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

10

9.1

• The outer shell electrons of an atom• Participate in chemical bonding

1A 1ns1

2A 2ns2

3A 3ns2np1

4A 4ns2np2

5A 5ns2np3

6A 6ns2np4

7A 7ns2np5

Group # of valence e-e- configuration

Valence Electrons

Page 11: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

11

G. N. Lewis

Developed the idea in 1902.

Lewis Structures

Page 12: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

12

Nitrogen, N, is in Group 5A and therefore has 5 valence electrons.

N:.

..

:

N .. ..N :.

. :N ...

Place one dot per valence electron on each of the four sides of the element symbol.

Pair the dots (electrons) until all of the valence electrons are used.

Lewis Dot Symbols

Page 13: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

13

Lewis Dot Symbols

Page 14: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

14

The Octet RuleChemical compounds tend to form so that each atom, by gaining, losing, or sharing electrons, has eight electrons in its highest occupied energy level.

The same number of electrons as in the nearest noble gas

The first exception to this is hydrogen, which follows the duet rule.

The second exception is helium which does not form bonds because it is already “full” with its two electrons

Page 15: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

15

Li + F Li+ F -

Ionic Bond

1s22s11s22s22p5 1s21s22s22p6[He][Ne]

Li

1s 2s 2p

F

1s 2s 2p

+

Li+

1s 2s 2p

F-

1s 2s 2p+

Page 16: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

16

Lattice energy (E) increases as Q increases and/or

as r decreases.

cmpd lattice energyMgF2

MgO

LiF

LiCl

2957

3938

1036

853

Q= +2,-1

Q= +2,-2

r F < r Cl

Electrostatic (Lattice) Energy

E = kQ+Q-r

Q+ is the charge on the cation

Q- is the charge on the anionr is the distance between the ions

Lattice energy (E) is the energy required to completely separate one mole of a solid ionic compound into gaseous ions.

Page 17: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

17

A chemical bond in which two or more electrons are shared by two atoms.

How should two atoms share electrons?

F F+

7e- 7e-

F F

8e- 8e-

F F

F F

Lewis structure of F2

lone pairslone pairs

lone pairslone pairs

single covalent bond

single covalent bond

Covalent Bond

Page 18: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

18

Distribution of electron density of H2

H H

Page 19: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

19

8e-

H HO+ + OH H O HHor

2e- 2e-

Lewis structure of water

Double bond – two atoms share two pairs of electrons

single covalent bonds

O C O or O C O

8e- 8e-8e-double bonds double bonds

Triple bond – two atoms share three pairs of electrons

N N8e-8e-

N N

triple bondtriple bond

or

Page 20: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

20

H F FH

A covalent bond with greater electron density around one of the two atoms

electron richregion

electron poorregion e- riche- poor

+ -

Polar Covalent Bond

Page 21: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

21

Electron density distributions in

H2, F2, and HF.

Page 22: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

22

Electronegativities (EN)

The ability of an atom in a molecule to attract shared electrons to itself

Linus Pauling 1901 - 1994

Page 23: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

23

Covalent

share e-

Polar Covalent

partial transfer of e-

Ionic

transfer e-

Increasing difference in electronegativity

Classification of Bonds

Difference in EN Bond Type

0 Covalent

2 Ionic

0 < and <2 Polar Covalent

Page 24: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

24

Classify the following bonds as ionic, polar covalent, or covalent: The bond in CsCl; the bond in H2S; andthe NN bond in H2NNH2.

Cs – 0.7 Cl – 3.0 3.0 – 0.7 = 2.3 Ionic

H – 2.1 S – 2.5 2.5 – 2.1 = 0.4 Polar Covalent

N – 3.0 N – 3.0 3.0 – 3.0 = 0 Covalent

Classification of Bonds

Page 25: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

25

1. Draw skeletal structure of compound showing what atoms are bonded to each other. Put least electronegative element in the center.

2. Count total number of valence e-. Add 1 for each negative charge. Subtract 1 for each positive charge.

3. Use one pair of electrons to form a bond (a single line) between each pair of atoms.

4. Arrange the remaining electrons to satisfy an octet for all atoms (duet for H), starting from outer atoms.

5. If a central atom does not have an octet, move in lone pairs to form double or triple bonds on the central atom as needed.

Rules for Writing Lewis Structures

Page 26: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

26

Write the Lewis structure of nitrogen trifluoride (NF3).

Step 1 – N is less electronegative than F, put N in center

F N F

F

Step 2 – Count valence electrons N - 5 (2s22p3) and F - 7 (2s22p5)

5 + (3 x 7) = 26 valence electrons

Step 3 – Draw single bonds between N and F atoms.

Step 4 – Arrange remaining 20 electrons to complete octets

Page 27: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

27

Write the Lewis structure of the carbonate ion (CO32-).

Step 1 – C is less electronegative than O, put C in center

O C O

O

Step 2 – Count valence electrons C - 4 (2s22p2) and O - 6 (2s22p4) -2 charge – 2e-

4 + (3 x 6) + 2 = 24 valence electrons

Step 3 – Draw single bonds between C and O atoms

Step 4 - Arrange remaining 18 electrons to complete octets

Step 5 – The central C has only 6 electrons. Form a double bond.

2

Page 28: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

28

More than one valid Lewis structures can be written for a particular molecule

The actual structure of the carbonate ion is an average of the three resonance structures

O C O

O

- -O C O

O

-

-

OCO

O

-

-

Resonance

2 2 2

Page 29: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

29

Exceptions to the Octet Rule

The Incomplete Octet

H HBeBe – 2e-

2H – 2x1e-

4e-

BeH2

BF3

B – 3e-

3F – 3x7e-

24e-

F B F

F

3 single bonds (3x2) = 69 lone pairs (9x2) = 18

Total = 24

Page 30: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

30

Exceptions to the Octet Rule

Odd-Electron Molecules

N – 5e-

O – 6e-

11e-

NO N O

The Expanded Octet (central atom with principal quantum number n > 2)

SF6

S – 6e-

6F – 42e-

48e-

S

F

F

F

FF

F

6 single bonds (6x2) = 1218 lone pairs (18x2) = 36

Total = 48

Page 31: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

31

Bond Type

Bond Length

(pm)

C-C 154

CC 133

CC 120

C-N 143

CN 138

CN 116

Covalent Bond Lengths

Bond Lengths

Triple bond < Double Bond < Single Bond

Page 32: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

32

The energy required to break a particular bond in one mole of gaseous molecules is the bond energy.

H2 (g) H (g) + H (g) 436.4 kJ

Cl2 (g) Cl (g)+ Cl (g) 242.7 kJ

HCl (g) H (g) + Cl (g) 431.9 kJ

O2 (g) O (g) + O (g) 498.7 kJ O O

N2 (g) N (g) + N (g) 941.4 kJ N N

Bond Energy

Bond Energies

Single bond < Double bond < Triple bond

Covalent Bond Energy

Page 33: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

33

Frequency in Hz

3 x 1020 3 x 1016 3 x 1012 3 x 108 3 x 104

DissociationIonization

Vibration

Rotation

Light-Matter Interactions

Page 34: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

34

Vibrational Modes of WaterInfrared light

Page 35: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

35

Infrared Spectrum of Water

100015002000

Wavenumber (cm-1)

Abs

orba

nce

100020003000

Liquid

Gas

Reveal the interactions between molecules and their environments

Page 36: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

36

Infrared Spectrum of Caffeine

100020003000

Wavenumber (cm-1)

Abs

orba

nce

Identification of compounds

Page 37: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

37

Lab 1

Page 38: 1 When Atoms Meet. 2 Bonding Forces  Electron – electron repulsive forces  Nucleus – nucleus repulsive forces  Electron – necleus attractive forces

38

Acknowledgment

Some images, animation, and material have been taken from the following sources:

Chemistry, Zumdahl, Steven S.; Zumdahl, Susan A.; Houghton Mifflin Co., 6th Ed., 2003;

supplements for the instructor

General Chemistry: The Essential Concepts, Chang, Raymon; McGraw-Hill Co. Inc., 4th

Ed., 2005; supplements for the instructor

Principles of General Chemistry, Silberberg, Martin; McGraw-Hill Co. Inc., 1st Ed., 2006;

supplements for the instructor

NIST WebBook: http://webbook.nist.gov/

http://www.lsbu.ac.uk/water/vibrat.html

http://en.wikipedia.org/wiki/Caffeine

http://www.wilsonhs.com/SCIENCE/CHEMISTRY/MRWILSON/Unit%204%20Chemical%2

0Bonding%20Powerpoint1.ppt