8/13/2019 Lecture 2 Bonding and Properties

1/18

ISSUES TO ADDRESS...

What promotes bonding?

What types of bonds are there?

What properties are formed from bonding?

1

BONDING AND PROPERTIES

8/13/2019 Lecture 2 Bonding and Properties

2/18

Nucleus: Z = # protons

2

orbital electrons:

n = principalquantum number

n=3 21

= 1 for hydrogen to 94 for plutoniumN = # neutrons

Atomic mass A Z + N

Adapted from Fig. 2.1,

Callister 6e.

BOHR ATOM

8/13/2019 Lecture 2 Bonding and Properties

3/18

have discrete energy states tend to occupy lowest available energy state.

3

Electrons...

ELECTRON ENERGY STATES

8/13/2019 Lecture 2 Bonding and Properties

4/18

4

have complete s and p subshells

tend to be unreactive.

Stable electron configurations...

Adapted from Table 2.2,

Callister 6e.

STABLE ELECTRON CONFIGURATIONS

8/13/2019 Lecture 2 Bonding and Properties

5/18

5

Why? Valence(outer) shell usually not filled completely.

Most elements: Electron configuration not stable.

Electron configuration1s1

1s2 (stable)1s22s11s22s21s22s22p 1

1s2

2s2

2p2

...

1s22s22p 6 (stable)1s22s22p 63s11s22s22p 63s21s22s22p 63s23p 1...

1s22s22p 63s23p 6 (stable)...

1s22s22p 63s23p 63d 104s246 (stable)

Adapted from Table 2.2,

Callister 6e.

SURVEY OF ELEMENTS

8/13/2019 Lecture 2 Bonding and Properties

6/18

6

Columns: Similar ValenceStructure

Electropositive elements:

Readily give up electronsto become + ions.

Electronegative elements:

Readily acquire electronsto become - ions.

Adapted from

Fig. 2.6,

Callister 6e.

THE PERIODIC TABLE

8/13/2019 Lecture 2 Bonding and Properties

7/18

7

Ranges from 0.7to 4.0,

Smaller electronegativity Larger electronegativity

Large values: tendency to acquire electrons.

Adapted from Fig. 2.7, Callister 6e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the Chemical

Bond, 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell

University.

ELECTRONEGATIVITY

8/13/2019 Lecture 2 Bonding and Properties

8/18

8

Occurs between + and - ions.

Requires electron transfer. Large difference in electronegativity required.

Example: NaCl

IONIC BONDING

8/13/2019 Lecture 2 Bonding and Properties

9/18

9

Predominant bonding in Ceramics

Give up electrons Acquire electrons

He-

Ne-

Ar-

Kr-

Xe-

Rn-

F4.0

Cl3.0

Br2.8

I2.5

At2.2

Li1.0

Na0.9

K0.8

Rb0.8

Cs0.7

Fr0.7

H2.1

Be1.5

Mg1.2

Ca1.0

Sr1.0

Ba0.9

Ra0.9

Ti1.5

Cr1.6

Fe1.8

Ni1.8

Zn1.8

As2.0

CsCl

MgO

CaF2

NaCl

O3.5

Adapted from Fig. 2.7, Callister 6e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the Chemical

Bond, 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell

University.

EXAMPLES: IONIC BONDING

8/13/2019 Lecture 2 Bonding and Properties

10/18

10

Requires shared electrons

Example: CH4

C: has 4 valence e,

needs 4 more

H: has 1 valence e,needs 1 more

Electronegativities

are comparable.

Adapted from Fig. 2.10, Callister 6e.

COVALENT BONDING

8/13/2019 Lecture 2 Bonding and Properties

11/18

11

Molecules with nonmetals

Molecules with metals andnonmetals

Elemental solids (RHS of Periodic Table)

Compound solids (about column IVA)

He-

Ne-

Ar-

Kr-

Xe-

Rn-

F4.0

Cl3.0

Br2.8

I2.5

At2.2

Li1.0

Na0.9

K0.8

Rb0.8

Cs0.7

Fr0.7

H2.1

Be1.5

Mg1.2

Ca1.0

Sr1.0

Ba0.9

Ra0.9

Ti1.5

Cr1.6

Fe1.8

Ni1.8

Zn1.8

As2.0

SiC

C(diamond)

H2O

C2.5

H2

Cl2

F2

Si1.8

Ga1.6

GaAs

Ge1.8

O2.0

column

IVA

Sn1.8

Pb1.8

Adapted from Fig. 2.7, Callister 6e. (Fig. 2.7 is

adapted from Linus Pauling, The Nature of the Chemical Bond, 3rd edition, Copyright 1939 and1940, 3rd edition. Copyright 1960 by Cornell University.

EXAMPLES: COVALENT BONDING

8/13/2019 Lecture 2 Bonding and Properties

12/18

12

Arises from a sea of donated valence electrons

(1, 2, or 3 from each atom).

Primary bond for metals and theiralloys

Adapted from Fig. 2.11, Callister 6e.

METALLIC BONDING

8/13/2019 Lecture 2 Bonding and Properties

13/18

13

Arises from interaction between dipoles

Permanent dipoles-molecule induced

Fluctuating dipoles

-general case:

-ex: liquid HCl

-ex: polymer

Adapted from Fig. 2.13, Callister 6e.

Adapted from Fig. 2.14,

Callister 6e.

Adapted from Fig. 2.14,

Callister 6e.

SECONDARY BONDING

8/13/2019 Lecture 2 Bonding and Properties

14/18

14

Type

Ionic

Covalent

Metallic

Secondary

Bond Energy

Large!

Variable

large-Diamond

small-Bismuth

Variable

large-Tungsten

small-Mercury

smallest

Comments

Nondirectional (ceramics)

Directional

semiconductors, ceramics

polymer chains)

Nondirectional (metals)

Directional

inter-chain (polymer)

inter-molecular

SUMMARY: BONDING

8/13/2019 Lecture 2 Bonding and Properties

15/18

15

Bond length, r

Bond energy, Eo

FF

r

Melting Temperature, Tm

Tmis larger if Eois larger.

PROPERTIES FROM BONDING: TM

8/13/2019 Lecture 2 Bonding and Properties

16/18

16

Elastic modulus, E

E ~ curvature at ro

LF

Ao= E

Lo

Elastic modulus

r

larger Elastic Modulus

smaller Elastic Modulus

Energy

rounstretched length

E is larger if Eois larger.

PROPERTIES FROM BONDING: E

8/13/2019 Lecture 2 Bonding and Properties

17/18

17

Coefficient of thermal expansion, a

a~ symmetry at ro

ais larger if Eois smaller.

= a (T2-T1)L

Lo

coeff. thermal expansion

PROPERTIES FROM BONDING: a

8/13/2019 Lecture 2 Bonding and Properties

18/18

18

Ceramics

(Ionic & covalent bonding):

Metals

(Metallic bonding):

Polymers

(Covalent & Secondary):

Large bond energy

large Tm

large Esmall a

Variable bond energy

moderate Tm

moderate Emoderate a

Directional Properties

Secondary bonding dominates

small Tsmall Elarge a

SUMMARY: PRIMARY BONDS