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CHAPTERCHAPTER 2:2:

InteratomicInteratomic BondinBondin

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e ruc ure o e om

Atom consists of nucleus encircled by moving electrons

The atomic number of an element is equal to the number of

electrons or protons in each atom.

of protons and neutrons in the atom.

The Avogadro number of an element is the number of atoms or

mo ecu es n a mo e.

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Atomic Models

2003Brooks/Cole

Publishing/ThomsonLearning

The atomic structure of sodium, atomic number 11, showing the electrons in the K,

L, and Mquantum shells

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THE PERIODIC TABLE Columns: Similar Valence Structure

6

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ELECTRONEGATIVITY Ranges from 0.7 to 4.0,

Large values: tendency to acquire electrons.

Smaller electronegativity Larger electronegativity

7

Electropositive elements:

Readily give up electrons

to become + ions.

Electronegative elements:

Readily acquire electrons

to become - ions.

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E = Bondin Enerr = E uil ibrium se arationEnergy @ r0 requiredto separate two atoms

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Basics of atomic bonding in solid state

Cr stal is a solid com osed of atoms ionsor molecules that demonstrate long rangeperiodic order in three dimensions

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Effect of temperature

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IONIC BONDING Occurs between + and - ions.

Requires electron transfer.

arge erence n e ec ronega v y requ re . Example: NaCl

Na (metal)

unstable

Cl (nonmetal)

unstableelectron

-CoulombicAttraction

stable

an on

stable

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IONIC BONDING

2003 Brooks/Cole Publishing / Thomson Learning

electronegativities. When sodium donates its valence electron to chlorine, eachbecomes an ion; attraction occurs, and the ionic bond is formed

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EXAMPLES: IONIC BONDING Predominant bonding in Ceramics

Give up electrons Acquire electrons

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Ionic Bonding is Nondirectional.

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COVALENT BONDING

Requires shared electrons

Example: CH4

C: has 4 valence e,

shared electronsfrom carbon atom

HCH4

H: has 1 valence e,

HH C

Electronegativities

are comparable.

shared electronsfrom hydrogenatoms

H

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COVALENT BONDING2003Brooks/ColePublishing/ThomsonLearning

Covalent bonding requires that electrons be shared between atoms in such a waythat each atom has its outer sporbital filled. In silicon, with a valence of four, fourcovalent bonds must be formed

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EXAMPLES: COVALENT BONDING

Molecules with nonmetals emen a so s o er o c a e

Compound solids (aboutcolumn IVA)

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Covalent Bonding:Covalent Bonding:

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METALLIC BONDING r ses rom a sea o ona e va ence e ec rons(1, 2, or 3 from each atom).

2003Brooks/ColePub

lishin

The metallic bond formswhen atoms ive u their

/ThomsonLearnin

valence electrons, which thenform an electron sea. Thepositively charged atom

attraction to the negativelycharged electrons

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SECONDARY BONDINGArises from interaction between dipoles

Fluctuating dipolesex: liquid H2

HH HH

H2 H2

clouds

+ - + -

Permanentdi oles-molecule induced

secondarybonding

bonding

+ - secondarybonding

+ --general case:

H Cl H Cl

secondary

bonding

se

-ex: liquid HCl

arybonding-

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SUMMARY: BONDINGType Bond Energy Comments

Variable

DirectionalCovalent large-Diamond

small-Bismuthsemiconductors, ceramics

polymer chains)

MetallicVariable

large-Tungsten Nondirectional (metals)sma - ercury

Directional-

inter-molecular

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Summary (Chapter 1-2)

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SUMMARY: PRIMARY BONDS

Ceramics Large bond energy

(Ionic & covalent bonding):

large Esmall a

Metals

(Metallic bonding):

Variab le bond energymoderate Tm

moderate Emoderate a

(Covalent & Secondary):

seco

Secondary bonding dominatessmall Tmsmall E

ybonding large a

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Reading Assignment:CHAPTER 2: Atomic Structure and Interatomic Bondingof Callister

Fundamental Concepts ec rons n oms The Periodic Table Bonding Forces and Energies

Secondary Bonding