L2. ATOMIC BONDING (post)maecourses.ucsd.edu/~jmckittr/mae20-wi11/C2-Atomic... · 2011-01-03 · 3...

1

1Chapter 2: Atomic bonding and properties

Atomic models

2Chapter 2: Atomic bonding and properties

Quantum numbers

•

p orbital

m1 = -1,0,+1

•

••

•

•

••

1/2

-1/2

s orbital

m1 = 0

m2 = -2,-1,0,+1,+2

d orbital

2

3Chapter 2: Atomic bonding and properties

p

d

f

s

4Chapter 2: Atomic bonding and properties

1s 2s 2pC

••••

•

•

↑

↓

2p

N

•

↑

↑

••••

•

•• ↓

O

↑

↓

•

↑

••••

•

•• ↓

• F

↑

↑

↓

•

↑

••••

•

•• ↓

•

•

Ne• inert gas• filled shell

↓

↓

↑

↑

↓

•

↑

••••

•••

•

••

+ 12 •↑

H+

••

↑

↓

+ 12

! 12

He

•••↑

Li

•••↑

↓•

Mg B

••••

↑•

3

5Chapter 2: Atomic bonding and properties

O

Se

Te

Po At

I

Br

He

Ne

Ar

Kr

Xe

Rn

F

ClS

Li Be

H

Na Mg

BaCs

RaFr

CaK Sc

SrRb Y

The Periodic Table• Columns: Similar Valence Structure

give

up

1egi

ve u

p 2e

give

up

3e iner

t gas

esac

cept

1e

acce

pt 2

e

6Chapter 2: Atomic bonding and properties

Electronegativity

Larger electronegativitySmaller electronegativity

4

7Chapter 2: Atomic bonding and properties

Force and energy vs. separation distance

8Chapter 2: Atomic bonding and properties

• Predominant bonding in ceramics

Ionic bonding

Give up electrons Acquire electrons

NaClMgOCaF2CsCl

5

9Chapter 2: Atomic bonding and properties

Covalent bonds

••

••• •

••C

H

HH

H

sharedelectronfrom H

sharedelectronfrom C

Sharing of electrons fromone atom to another

10Chapter 2: Atomic bonding and properties

Metallic bonds 'Cloud' of electrons

electron cloudaround + cores

Secondary bonds• Permanent dipoles-molecule induced

-general case:

-ex: liquid HCl

-ex: polymer

H Cl H Clsecondary bonding

secondary bonding

secondary bondingsecondary bonding

6

11Chapter 2: Atomic bonding and properties

Contribution of bond types

Metals

covalent

ionic

secondary

Polymers

Semiconductors

metallic

Ceramics and glasses

12Chapter 2: Atomic bonding and properties

• Bond length, r

• Bond energy, Eo

• Melting Temperature, Tm

Properties from bonding: Tm

r o r

Energyr

larger Tm

smaller Tm

Eo = “bond energy”

Energy

r o runstretched length

7

13Chapter 2: Atomic bonding and properties

• Coefficient of thermal expansion, α

Properties from bonding: α

ΔL

length, Lo

unheated, T1

heated, T2

r or

larger α

smaller α

Energyunstretched length

EoEo