Week-1 Atomic Structure and Inter Atomic Bonding

8/2/2019 Week-1 Atomic Structure and Inter Atomic Bonding

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3/15/20121

Atomic Structure and InteratomicBonding:

Callister Chapter 2

• What promotes bonding? • What types of bonds are there?

• What properties are conditional from bonding?

consider carbon: graphite and diamond

graphite – soft, "greasy"

diamond – hardest material known

• How are atoms arranged?

atomic structure



2

Atomic Structure

• atom – electrons – 9.11 x 10-31 kgprotons neutrons

• 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 6.023 x 1023 molecules or atoms

1 amu/atom = 1g/mol

CH

12.011

1.008 etc.Bohr model ofatomic structure

ElectronCloud

Nucleus



3/15/201233

Atomic Structure

• Valence electrons determine all of thefollowing properties

1) Chemical

2) Electrical3) Thermal

4) Optical



4

Electronic Structure

• Electrons have wavelike and particulateproperties.

– This means that electrons are in orbitals defined by aprobability.

– Each orbital at discrete energy level determined byquantum 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)

m l = magnetic 1, 3, 5, 7 (-l to +l)

m s = spin ½, -½

Bohr & Schrodinger



5

Electron Energy States

1s

2s 2p

K -shell n = 1

L-shell n = 2

3s 3p M -shell n = 3

3d

4s

4p 4d

Energy

N -shell n = 4

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

Electrons...

Adapted from Fig. 2.4,Callister 7e.

I n c r e a s i n g

e n e r g y

l e v e l s



The number of available electron in some of theelectron shell and sub shells



Electron Configurations

• Valence electrons – those in unfilled shells• Filled shells more stable

• Valence electrons are most available forbonding and tend to control the chemical

properties

– example: C (atomic number = 6)

1s 2 2s 2 2p 2

valence electrons



8

Electronic Configurations

ex: Fe - atomic # =

26

Adapted from Fig. 2.4,

Callister 7e.

1s

2s 2p

K -shell n = 1

L-shell n = 2

3s 3p M -shell n = 3

3d

4s

4p 4d

Energy

N -shell n = 4

1s 2 2s 2 2p 6 3s 2 3p 6 3d 6 4s 2

Valenceelectrons

I n c r e a s i n g

e n e r g y

l e v e l s



3/15/20129

The Periodic Table• Columns: Similar Valence Structure

Adapted fromFig. 2.6,Callister 7e.

g i v e

u p 1 e

g i v e

u p

2 e

g i v e

u p

3 e

i n e r t g a s e s

a c c e p t 1 e

a c c e p t 2 e

O

Se

Te

Po At

I

Br

He

Ne

Ar

Kr

Xe

Rn

F

ClS

Li Be

H

Na Mg

BaCsRaFr

CaK Sc

SrRb Y

Elements of Group IA have one valence electron.Elements in Group 4A have four valence electrons, etc





3/15/201211

Smaller electronegativity Larger electronegativityAdapted from Fig. 2.7, Callister 7e. (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

• Electronegativity is the ability of an atom toattract electrons to itself.



Interactions between atoms

• Electrons in the outermost levels interact first.• When the outer shells are unfilled, atoms

gain, lose, or borrow electrons which is thebasis of bonding.

Eg NaCl



13

BondingProperties

13

Ionic bond – metal + nonmetal

donates acceptselectrons electrons

Dissimilar electronegativities

ex: MgO Mg 1s 2 2s 2 2p 6 3s 2 O 1s 2 2s 2 2p 4

[Ne] 3s 2

Mg2+ 1s 2 2s 2 2p 6 O2- 1s 2 2s 2 2p 6 [Ne] [Ne]



14

• Occurs between + and - ions.

• Requires electron transfer. • Large difference in electronegativity require• Example: NaCl

Ionic Bonding

Na (metal)unstable

Cl (nonmetal)unstable

electron

+ -

Coulombic Attraction

Na (cation)stable

Cl (anion)stable



1515

Ionic Bonding

• Energy – minimum energy most stable – Energy balance of attractive and repulsive terms

Attractive energy E A

Net energy E N

Repulsive energy E R

Interatomic separation r

r A

n r B

E N = E A + E R = + -

Adapted from Fig. 2.8(b),Callister & Rethwisch 8e.



16

• Predominant bonding in Ceramics

Adapted from Fig. 2.7, Callister 7e. (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

CaF2CsCl



Chapter 2 -

3/15/201217

C: has 4 valence e - ,needs 4 more

H: has 1 valence e - ,needs 1 more

Methane gas .

Adapted from Fig. 2.10, Callister 7e.

Covalent Bonding• similar electronegativity share electrons

• bonds determined by valence – s & p orbitalsdominate bonding

• Example: CH4shared electronsfrom carbon atom

shared electrons

from hydrogenatoms

H

H

H

H

C

CH4

Electronegativitiesare comparable.



3/15/2012 18

• NonMetallic ElementalMolecules; e.g. F2

• Hydrogen Compounds;e.g., HF, HNO3

• Elemental Solids; e.g.,C, Si, Ge

• Near Group-IVA SolidCompounds; e.g. GaAs

Covalent bonding

Covalent bonds are formed by sharing of the valence electronsCovalent bonds are very directional

Covalent bond model: an atom can have at most 8-N’ covalent

bonds, where N’ = number of valence electrons

Covalent bonds can be very strong, eg diamond, SiC, Si, etc,also can be very weak, eg Bismuth

Polymeric materials exhibit covalent type bonding.



19

• Electrons Shared By All Atoms

– “sea of electrons” around “ion cores”

• Ion Cores

– Atom Gives Up e- to the “sea”, leaving remaining

Atom with a Positive Ionic Charge

• The Ion contains the Large & Heavy Nucleusand is thus FIXED in Space

• Generally Apply to Electro-Positive Elements

– e.g.; Transition Metals such as Ti, Ni, Zn

Metallic bonding

A metallic bond is non-directional(bonds form in any direction)

atoms pack closely high density.



20http://207.10.97.102/chemzone/lessons/03bonding/mleebonding/metallicblue.gif

Metallic bonds may be weak or strong.

Bonding energies: range from 68 kJ/mol (0.7 eV/atom) forHg to 850 kJ/mol (8.8 eV/atom) for W.Melting temperatures: -39 C for Hg and 3410 C for W.

Metallic bonding

Metals can be reshaped high melting points

hardness electrical conductivity

http://www.launc.tased.edu.au/online/sciences/PhysSci/pschem/metals/Reshape.htm

http://www.launc.tased.edu.au/online/sciences/PhysSci/pschem/metals/Melt.htm

http://www.launc.tased.edu.au/online/sciences/PhysSci/pschem/metals/Hardness.htm

http://www.launc.tased.edu.au/online/sciences/PhysSci/pschem/metals/Elecond.htm

http://www.launc.tased.edu.au/online/sciences/PhysSci/pschem/metals/Elecond.htm

http://www.launc.tased.edu.au/online/sciences/PhysSci/pschem/metals/Hardness.htm

http://www.launc.tased.edu.au/online/sciences/PhysSci/pschem/metals/Melt.htm

http://www.launc.tased.edu.au/online/sciences/PhysSci/pschem/metals/Reshape.htm



21

Mixed Ionic+Covalent Bonding• Many Compounds Exhibit

Ionic-Covalent Mixed Bonding• semiconducting compounds such as GaAs, ZnSe

2

4100%

%Ionic 1 1

A B X X

e

--

- – where X A & X B are Pauling ElectroNegativities

• Example MgO: X Mg

= 1.2, X O

= 3.5

ionic73.4%(100%)xe1characterionic% 4

)2.15.3(

2

-

--



22

Determine how ionic the bonds between thefollowing atoms would be

Sodium andchlorine

Na E0 0.9Cl E0 3.0

Δ=2.168% ionic

Carbon andnitrogen

C E0 2.5

N E0 3.0

Δ=0.5

10% ionic

90%covalent

Potassium andsuphur

K E0 0.8

S E0 2.5

Δ=2.1

50% ionic

2

4100%

%Ionic 11

A B X X

e

--

-

XA XB % Ionic

electronegativity

chargesfrom

periodic table



Covalent vs Ionic Bonding

• The polarity of a covalentbond is the partial ioniccharacter

• Real bonds liesomewhere between ionic

and covalent• The difference in

electronegativitycorresponds directly to thepercent ionic character ofthe bond

Very few materials have pure ionic or covalent bonding;electronegativity inpart defines how much time electronsspend between ion cores…



24

Type Substance Energy(eV/atom)

Melt. Temp(°C)

IonicNaCl 3.3 801

MgO 5.2 2800

CovalentSi 4.7 1410

C 7.4 >3550

Metallic

Hg 0.7 -39

Al 3.4 660Fe 4.2 1538

W 8.8 3410

Bonding Energies and MeltingTemperatures



Dipole Forces• Electrostatic interactions

between adjacentmolecules are called

Dipole Forces• The most extreme form of

dipole forces result fromthe interaction of a

hydrogen atom with ahighly electronegativeatom resulting inhydrogen bonding.

Secondary bonding – Dipole Forces



Dispersion Forces (or Van der Waalsforces)

• Interactions resulting frommomentary concentration

variations in the electronclouds of adjacent atoms

• The interactions are briefand weak, but largemolecules (such as

polymers) haveopportunities for manysimultaneous interactions

http://www.elmhurst.edu/~chm/vchembook/122Adensityice.html



27

Hydrogen Bonding

Hydrogen bonding in HF

solid ice

liquid water

Special type of secondary

bonding, exists between somemolecules that have hydrogenas one of constituents

The increase in volume of ice is about9%. This increase causes enoughforce to break most rigid containers.

This is the same force, repeated on a daily basis, that creates "pot holes" in the roads inthe winter time.

p y



28Adapted from Fig. 2.14,Callister 6e.

•The dipole moment of water provides a "handle" forinteraction with microwave electric fields in a microwaveoven.

• Microwaves can add energy to the water molecules, theyvibrate and heat the compounds.

Secondary Bonding, Polar

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/diph2o.html

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/diph2o.html



29

C Bonding-Type → Properties

Diamond:covalent (directional) bonds

Graphite:covalent bonds within layersvan der Waals b/w layers

layers slide soft, greasy (lubricant)

hardest known material



• Bond energy, Eo

• Bond length, r

FF

r

• Melting Temperature, Tm

if bonding energy Eo is largemelting temperature Tmis large.

Properties from Bonding: TM



LF

Ao = E

Lo

Elastic modulus

r

larger Elastic Modulus

smaller Elastic Modulus

Energy

r o

unstretched length

Properties from Bonding: E• Elastic modulus, E

• E ~ curvature at r o if slope r=ro is steepModulus is high



• Coefficient of thermal expansion, a

= a(T2-T1)

L

Lo

coeff. thermal expansion

Properties from Bonding: a

• a ~ symmetry at ro Eg. Thermostats for central

heating

a is larger if E o is smaller.



Bonding Energies and MeltingTemperatures for Various Substances



34

Summary: Primary Bonds

Ceramics (Ionic & covalent bonding):

Metals (Metallic bonding):

Polymers

(Covalent & Secondary):

Large bond energylarge Tm large Esmall a

Variable bond energymoderate Tm moderate Emoderate a

Directional Properties

Secondary bonding dominatessmall Tm

small Elarge a



Reading:

The structure of crystalline solids Part I:Callister Chapter 3.

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Week-1 Atomic Structure and Inter Atomic Bonding