Atomic Bonding in Solids - ilearn Notes Module 3 2009_S1 Lecture_3_Atomic structure and interatomic bonding 1 Atomic Bonding in Solids 1. Ionic Bonding 2. Covalent Bonding

Module 3 2009_S1 Lecture_3_Atomic structure and interatomic bondingMaster Notes 1

Atomic Bonding in Solids

1. Ionic Bonding2. Covalent Bonding3. Metallic Bonding4. Mixed Bonding-

primary bonding

A. Primary bonding of matter

1. Van Der Waals

2. Hydrogen3. Polar

B. Secondary bonding of matter

http://cwx.prenhall.com/petrucci/medialib/media_portfolio/text_images/FG12_28.JPG

Molecular orbital representation of p bonding in benzene. A computer-generated model of the benzene molecule. The planar s bond framework is clearly visible. The p orbitals above and below the C and H plane are highlighted


Ionic Bonding• Ion ≡ An Atom That Has Gained/Lost e-(s)

– Resulting Ion has +/- CHARGE• Ionic Bonding Occurs Between + & - Ions

– Requires Electron TRANSFER; e.g. NaCl

Na (metal) Unstable

1s22s22p63s1

Na (cation) Stable

1s22s22p6

Cl (nonmetal) Unstable

1s22s22p63s23p5electron

CoulombicAttraction

Cl (anion) Stable

1s22s22p63s6

+ -

X

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1. Ionic bonding


Give up electrons Acquire electrons

He -

Ne -

Ar-

Kr-

Xe-

Rn-

F4.0

Cl3.0

Br 2.8

I2.5

At2.2

Li1.0

Na0.9

K0.8

Rb0.8

Cs0.7

Fr0.7

H 2.1

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

1. Ionic bonding

Predominant bonding in Ceramics


• Hard and brittle materials.• Common bonding for ceramic materials.• Electrically and thermally insulative materials.

• Properties of ionic bonding.• Nondirectional: magnitude of bond is equal in

all directions around the ion.• High bonding energies (~600 - 1500 kJ/mol).• Reflected in high melting temperatures.• eg NACl(common salt!)

1. Ionic bonding-summary


2. Covalent bonding

• Requires SHARED Electrons (Co-valent)

• Example is CH4(methane)

– C: has 4 valence e-’s, needs 4 more

– H: has 1 valence e-, needs 1 more

• Characteristics– If A compound, Then

Electronegativities are comparable

– ≥ 4 valence e-’s Cl2

shared electrons from carbon atom

shared electrons from hydrogen atoms

H

H

H

H

C

CH4

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2. Covalent bonding

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CoValent Bonding Examples• NonMetallic Elemental

Molecules; e.g. F2

• Hydrogen Compounds; e.g., HF, HNO3

• Elemental Solids; e.g., C, Si, Ge

• Near Group-IVA Solid Compounds; e.g. GaAs

He -Ne -Ar-Kr-Xe-Rn-

F4.0Cl3.0Br 2.8I2.5At2.2

Li1.0Na0.9K0.8Rb0.8Cs0.7Fr0.7

H 2.1Be1.5Mg1.2Ca1.0Sr1.0Ba0.9Ra0.9Ti1.5Cr1.6Fe1.8Ni1.8Zn1.8As2.0SiCC(diamond)H2O C 2.5H2 Cl2F2Si1.8Ga1.6

GaAsGe1.8

O2.0

co

lIV

A

Sn1.8Pb1.8


Diamond:

(each C atom has four covalent bonds with four other carbon atoms)

2. Covalent bondingOther elements: carbon

Covalent Bonding is strongly directional


Check :

• Offer an explanation as to why covalently bonded materials are generally less dense than ionically or metallically bonded ones.

• Answer: Covalently bonded materials are less dense than metallic or ionically bonded ones because covalent bonds are directional in nature whereas metallic and ionic are not;

• when bonds are directional, the atoms cannot pack together in as dense a manner, yielding a lower mass density.


Mixed Ionic+Covalent Bonding• Many Compounds Exhibit

Ionic-Covalent Mixed Bonding

( )

1%1001 Ionic-% 4

2

⋅⎟⎟⎠

⎞⎜⎜⎝

⎛−=

−− BA XX

e

– where XA & XB are Pauling ElectroNegativities

• Example MgO: XMg = 1.3, XO = 3.5

( )%2.70

1%1001 Ionic-% 4

5.33.1 2

=⋅⎟⎟⎠

⎞⎜⎜⎝

⎛−=

−−

e


• 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 Nucleus

and is thus FIXED in Space• Generally Apply to Electro-Positive Elements

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

3. Metallic bonding

Module 3 2009_S1 Lecture_3_Atomic structure and interatomic bondingMaster Notes 13http://207.10.97.102/chemzone/lessons/03bonding/mleebonding/metallicblue.gif

3. Metallic bonding

Valence electrons are not bound to any particular atom in the solid and are more or less free to drift throughout the entire metal.

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

→ atoms pack closely.

Module 3 2009_S1 Lecture_3_Atomic structure and interatomic bondingMaster Notes 14http://207.10.97.102/chemzone/lessons/03bonding/mleebonding/metallicblue.gif

3. Metallic bondingMetallic bonds may be weak or strong.Bonding energies: range from 68 kJ/mol (0.7 eV/atom) for Hg to 850 kJ/mol (8.8 eV/atom) for W.Melting temperatures: -39 C for Hg and 3410 C for W.

Stronger bonds lead to higher melting temperature:atomic scale property ⇒ macroscale property.


85 and 96 percent tin, and the rest copper and/or lead

3. Metals Form Alloys

Metals do not combine with metals. They form Alloys which is a solution of a

metal in a metal.Examples are steel, brass, bronze and pewter.?? an alloy of copper & zinc

an alloy of copper & tin

an alloy of iron, carbon +


34108.8W15384.2Fe6603.4Al-390.7Hg

Metallic

>35507.4C14104.7Si

Covalent

28005.2MgO8013.3NaCl

Ionic

Melt. Temp (°C)

Energy (eV/atom)

SubstanceType

Bonding Energies and Melting Temperatures


SUMMARY•COVALENT: Molecules with nonmetals.•Molecules with metals and nonmetals.

•Elemental solids (RHS of Periodic Table).•Compound solids (about column IVA).- directional

• IONIC: occurs between two elements with low difference in theirelectronegativities (usually non-metalics), outer electrons are shared amongst the four neighbouring atoms- non directional

Metallic bonding


Secondary Bonding• Arises from Atomic or

Molecular DIPOLES• What’s a DiPole?

– Separation of the + & - Charge-Centers• Generates an

ELECTRIC Field within the Entity

• Fluctuating DIPOLES– Charge Centers Due

to SHORT-LIVED Charge Asymmentry

E-Field

asymmetric electron clouds

+ - + -secondary

bonding

• Liquifying Force for Electrically Neutral and Symetrical Molecules such as H2, N2


Secondary Bonding cont.• Ionic Bonding in some

Molecules results in a PERMANENT Dipole

• The +/- End of These Polar Molecules can Then Attract the -/+ Ends of Other Polar Molecules

• General Case + - secondary bonding + -

H Cl H Clsecondary bonding

secondary bonding

• e.g.; HCl Liquid

• e.g.; PolymerSolid


Secondary Bonding, H Bond• Recall that H has in Only a

Single Proton and Electron – NO Neutrons

• When H forms an Ionic Bond, it Gives Up (for the most part) the e-

– This Leaves the Hydrogen’s p+ Ionic Core Unscreened by any e-’s

– This Forms a Molecule with a POSITIVE (and Negative end)

• This Proton-Induced Dipole is quite Strong and Can Lead to relatively powerful Dipole Bonding– Classic Example = H2O

to Form Liquid or Solid


Hydrogen bonding: a special type of secondary bond exists between some molecules which

have hydrogen as one of the constituents.

Example:hydrogen bond in water.

Secondary Bonding, H Bond

Module 3 2009_S1 Lecture_3_Atomic structure and interatomic bondingMaster Notes 22Adapted from Fig. 2.14,Callister 6e.

- water is a polar moleculebecause oxygen is more electronegative than hydrogen

•The dipole moment of water provides a "handle" for interaction with microwave electric fields in a microwave oven.• Microwaves can add energy to the water molecules, they vibrate and heat the compounds.

Secondary Bonding, Polar


C Bonding-Type → Properties

Diamond: covalent (directional) bonds→ hardest known material

Graphite: covalent bonds within layers van der Waals b/w layers→ layers slide → soft, greasy (lubricant)


TypeIonic

Covalent

Metallic

Secondary

Bond EnergyLarge!

Variablelarge-Diamondsmall-Bismuth

Variablelarge-Tungstensmall-Mercury

smallest

CommentsNondirectional (ceramics)High MP high E

Directionalsemiconductors, ceramics

(polymer chains)variable MP variable E

Nondirectional (metals)Variable MP “sea of electrons”Variable E

Directionalinter-chain (polymer)

inter-molecular Low E


Summary: Primary Bonds

Ceramics(Ionic & covalent bonding):

Metals(Metallic bonding):

Polymers(Covalent & Secondary):

secondary bonding

Large bond energylarge Tm

large Esmall α

Variable bond energymoderate Tm

moderate Emoderate α

Directional PropertiesSecondary bonding dominates

small Tm

small Elarge α


Water molecules in solid ice and liquid water

Water can rupture along a side panel bottom seam due to water being left in the can during a cold night and expanding as it froze and causing rupture

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3/19/2009 Module 4 The nano-structure of crystalline solids

Materials Taxonomy

Primary Materials Groups– Metals– Polymers– Ceramics

All other Materials are a COMBINATION or SUBSET of this BASE SET

1. Ionic Bonding2. Covalent Bonding3. Metallic Bonding4. Mixed Bonding-

primary bonding

1. Van Der Waals

2. Hydrogen3. Polar

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Atomic Bonding in Solids - ilearn Notes Module 3 2009_S1 Lecture_3_Atomic structure and interatomic bonding 1 Atomic Bonding in Solids 1. Ionic Bonding 2. Covalent Bonding