FIZIK 1_2

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An Introduction to Material Science:

The classification of materials, model

theory and atomic energy, atomicbonding, ion and molecules

An Introduction to Material Science:

The classification of materials,model theory and atomic energy,

atomic bonding, ion and molecules

Fakulti Kejuruteraan dan Alam BinaPhysics for Engineers

By Dr. Huda Abdullah

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model theory and atomic energy

atomic bonding ions and molecules

Lecture Outline

Physics for Engineers

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ISSUES TO ADDRESS...

What promotes bonding?

What types of bonds are there?

What properties are inferred from bonding?

Atomic Structure & Interatomic

Bonding


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Atomic Structure and Bonding

Atoms are composed of electrons, protons, and

neutrons. Electron and protons are negative and

positive charges of the same magnitude, 1.6 10-

19 Coulombs

Neutrons?

- have no charge

http://www.youtube.com/watch?v=zEX2aGpIDBY

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Electrons in Atoms

The forcesin the atom are repulsions between

electrons and attraction between electrons

and protons. The neutrons play no significant

role. Thus, Z is what characterizes the atom


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Fakulti Kejuruteraan dan Alam Bina 6Physics for Engineers

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Atomic Structure (Freshman Chem.)

Atom Electrons : 9.11 x 10

-31

kgProtonsNeutrons

Atomic number= # of protons in nucleus of atom= # of electrons of neutral species

A [=] atomic mass unit= amu = 1/12 mass of 12C

Atomic wt= wt of 6.022 x 1023molecules or atoms

1 amu/atom = 1g/mol

C 12.011H 1.008 etc.

}1.67 x 10-27kg

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Fakulti Kejuruteraan dan Alam Bina 8Physics for Engineers

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Physics for Engineers Fakulti Kejuruteraan dan Alam Bina 9

Example

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Atomic Structure

Valence electrons determine all of thefollowing properties

1) Chemical

2) Electrical3) Thermal

4) Optical


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Electronic Structure

Electrons have wavelikeand particulateproperties. This means that electrons are in orbitalsdefined by a

probability.

Each orbital at discrete energy level is determined by

quantum numbers.

Quantum # Designation

n= principal (energy level-shell) K, L, M, N, O (1, 2, 3, etc.)

l= subsidiary (orbitals) s,p, d,f (0, 1, 2, 3,, n -1)

ml= magnetic 1, 3, 5, 7 (-lto +l)

ms= spin , -

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The number of Available Electron States in Some of the

Electron Shells and Subshells

Fakulti Kejuruteraan dan Alam Bina

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Electron Energy States

1s

2s2p

K-shell n = 1

L-shell n = 2

3s3p M-shell n = 3

3d

4s

4p4d

Energy

N-shell n = 4

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

Electrons...

Adapted from Fig. 2.4,Callister & Rethwisch 8e.

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

Most elements: Electron configuration not stable.

SURVEY OF ELEMENTS

Electron configuration

(stable)

...

...

1s22s22p 63s23p6 (stable)...

1s22s22p 63s23p 63d 10 4s24p6 (stable)

Atomic #

18...

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Element1s11Hydrogen

1s22Helium1s22s13Lithium

1s22s24Beryllium

1s22s22p15Boron

1s2

2s2

2p2

6Carbon...

1s22s22p6 (stable)10Neon1s22s22p 63s111Sodium

1s22s22p 63s212Magnesium

1s22s22p 63s23p113Aluminum...

Argon...

Krypton

Adapted from Table 2.2,

Callister & Rethwisch 8e.

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Electron Configurations

Valence electronsthose in unfilled shells Filled shells more stable

Valence electrons are most available for bondingand tend to control the chemical properties

Example: C (atomic number = 6)

1s2 2s22p2

valence electrons


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Electronic Configurations

Ex: Fe- atomic # = 26

valence

electrons

Adapted from Fig. 2.4,


1s

2s2p

K-shell n = 1

L-shell n = 2

3s3p M-shell n = 3

3d

4s

4p4d

Energy

N-shell n = 4

1s2 2s2 2p6 3s23p6 3d6 4s2


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Check:

Fakulti Kejuruteraan dan Alam Bina

1. Why are the atomic weights of the elementsgenerally not integer? Cite two reasons

2. Give electron configurations for the

a) Fe3+

b) S2-

c) Mn3+

d) Ca

2+


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The Periodic Table Columns: Similar ValenceStructure

Adapted from

Fig. 2.6,

Callister &

Rethwisch 8e.

Electropositive elements:

Readily give up electrons to become + ions.

Electronegative elements:

Readily acquire electrons to become - ions.

give

up1

e-

give

up

2e-

give

up

3e-

inertgas

es

accept1e-

accept2e-

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


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Ranges from 0.7to 4.0

Smaller electronegativity Larger electronegativity

Large values: tendency to acquire electrons.

Adapted from Fig. 2.7, Callister & Rethwisch 8e. (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


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Ionic bond metal + nonmetal

donates acceptselectrons electrons

Dissimilar electronegativities

Ex: MgOMg 1s22s22p63s2 O 1s22s22p4

[Ne] 3s2

Mg2+ 1s22s22p6 O2- 1s22s22p6

[Ne] [Ne]


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Occurs between + and - ions.

Requires electron transfer.

Large difference in electronegativity required.

Example: NaCl

Ionic Bonding

Na (metal)

unstable

Cl (nonmetal)

unstable

electron

+ -Coulombic

Attraction

Na (cation)

stableCl (anion)

stable


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Ionic Bonding

Energyminimum energy most stable

Energy balance of attractiveand repulsiveterms

Attractive energy EA

Net energy EN

Repulsive energy ER

Interatomic separation r

rA

nrB

EN= EA+ ER=

Adapted from Fig. 2.8(b),



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Bonding Force and Energy


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Predominant bonding in Ceramics

Adapted from Fig. 2.7, Callister & Rethwisch 8e. (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

Give up electrons Acquire electrons

NaCl

MgO

CaF 2

CsCl


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C: has 4 valence e-,

needs 4 more

H: has 1 valence e-,

needs 1 more

Electronegativitiesare comparable.

Adapted from Fig. 2.10, Callister & Rethwisch 8e.

Covalent Bonding

Similar electronegativity share electrons

Bonds determined by valences&porbitals dominate bonding

Example: CH4

shared electronsfrom carbon atom

shared electrons

from hydrogenatoms

H

H

H

H

C

CH4


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Primary Bonding

Metallic Bond-- delocalized as electron cloud

Ionic-Covalent Mixed Bonding

% ionic character=

whereXA&XBare Pauling electronegativities

%)100(x1 e(XA XB )

2

4

ionic73.4%(100%)xe1characterionic% 4)2.15.3(

2

Ex: MgO XMg= 1.2XO = 3.5


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Arises from interaction between dipoles

Permanent dipoles-molecule induced

Fluctuating dipoles

-general case:

-ex: liquid HCl

-ex: polymer





Secondary Bonding

asymmetric electronclouds

+ - + -secondarybonding

HH HH

H 2 H 2

secondarybonding

ex: liquid H 2

H Cl H Clsecondarybonding

secondarybonding

+ - + -

secondary bonding


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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


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Bond length, r

Bond energy, Eo

Melting Temperature, Tm

Tmis larger if Eois larger.

Properties From Bonding: Tm

ro r

Energy

r

larger Tm

smaller Tm

Eo =

bond energy

Energy

r

o r

unstretched length


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Coefficient of thermal expansion,

~ symmetric at ro

is larger if Eois smaller.

Properties From Bonding :

= (T2-T1)L

Lo

coeff. thermal expansion

L

length, Lo

unheated, T1

heated, T2

ro r

smaller

larger

Energy

unstretched length

E

oE

oPh i f E i

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