Atomic Structure(2008) (Chapter 1)

8/12/2019 Atomic Structure(2008) (Chapter 1)

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ATOMIC STRUCTURE


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Learning Objective

You should be able:

Configure electron configuration

Differentiate between each atomic bondingBriefly describe ionic, covalent, metallic,

hydrogen and van der waals bonds

Relate the atomic bonding with materialproperties


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Use Your Previous

Knowledge on:

Subatomic particle

Atomic numberAtomic mass

Isotopes and isobar


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AtomicStructure


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AtomicStructure


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Electron configuration

electron configuration is thearrangement of electrons in atom,molecule

Knowledge of the electronconfiguration of different atoms is

useful:understanding the structure of the

periodic table of elements.

describing the chemical bonds that hold


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Stable configuration

Stable elements have equal numbersof

Electrons

Protons Neutrons

Stable elements have a neutral

charge 1 Electron (-) plus

1 Proton (+) plus

1 Neutron (0) =

NO CHARGE


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lectron onfigur tionelectron configurationis the arrangement of

electronsin an atom, moleculeor otherbody

Electrons are on the shells around thenucleus.

Each shell has a name

The first shell is k

Followed by l, m, n, o, p & q
http://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Atomhttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Atomhttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/Atomhttp://en.wikipedia.org/wiki/Electron


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Shells hold only a limited number of electrons

Different shells hold different numbers

K holds only 2 electrons

L holds 8 electrons

M holds up to 18 electrons

Each shell (energy level) consist of subshell

(sublevel). Each type of sublevel holds a different orbitals.

An orbital is a space that can be occupied by up to

two electrons


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The number of available electron states in some of the electron shells and

subshells

Principal

Quantum

number, n

Shell

Designation

Subshells Number of

states

Number of electron

Per subshell Per shell

1 K s 1 2 2

2 L s 1 2 8

p 3 6

3 M s 1 2 18

p 3 6

d 5 10

4 N s 1 2 32

p 3 6

d 5 10

f 7 14


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Atomic Bonding in solids

Three types of primary or chemical bondare found in solids

Ionic

Covalent inter atomic bonding Metallic

Secondary Bonding Van der Waals

Hydrogen Bonding


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Ionic Bonding Electron are transferred to form a bond

Often found in compounds composed ofelectropositive elements (metals) and

electronegative elements (non metals)

Na valance

+1

Cl valance -1


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Crystal structure of ionic material


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9

Predominant bonding in Ceramics

Give up electrons Acquire electrons

He-

Ne-

Ar-

Kr-

Xe-

Rn-

F4.0

Cl3.0

Br2.8

I2.5

At2.2

Li1.0

Na0.9

K0.8

Rb0.8

Cs0.7

Fr0.7

H2.1

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

EXAMPLES: IONIC BONDING


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General characteristic and

propertiesCharacteristic

Non-directional Bond and strong bond.

Bonding Energy 150-370 Kcal/mol

Examples- NaCl 183 Kcal/mol, LiF 240 Kcal/mol

Properties

Generally solids at room temperature

High melting and boiling point The no. of charge on the ions

The size of ions


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Hard

brittle

Poor conductors of electricity in solid state

Good conductor in solution or whenmolten


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Covalent Bonding

Electrons are shared to form a bond
http://en.wikipedia.org/wiki/Image:Covalent.svg


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11

Molecules with nonmetals Molecules with metals andnonmetals Elemental solids

Compound solids (about column IVA)

He-

Ne-

Ar-

Kr-

Xe-

Rn-

F4.0

Cl3.0

Br2.8

I2.5

At2.2

Li1.0

Na0.9

K0.8

Rb0.8

Cs0.7

Fr0.7

H2.1

Be1.5

Mg1.2

Ca1.0

Sr1.0

Ba0.9

Ra0.9

Ti1.5

Cr1.6

Fe1.8

Ni1.8

Zn1.8

As2.0

SiC

C(diamond)

H2O

C2.5

H2

Cl2

F2

Si1.8

Ga1.6

GaAs

Ge1.8

O2.0

column

IVA

Sn1.8

Pb1.8

Adapted from Fig. 2.7, Callister 6e. (Fig. 2.7 is

adapted from Linus Pauling, The Nature of the Chemical Bond, 3rd edition, Copyright 1939 and1940, 3rd edition. Copyright 1960 by Cornell University.

EXAMPLES: COVALENT BONDING


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Covalent Bonding General Characteristics

Bonding energy 75-300 Kcal/mol

Covalent bonding most frequently occursbetween atoms with similar electronegativities.

Directional bond-strength of bond is not equalin all directions ( atoms do not connect in alldirection)

Low or No electrical conductivity

Very hard, high melting temperature Examples Si 84 Kcal/mol, GaAs 75 Kcal/mol,

Diamond 170 Kcal/mol


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Metallic Bonding

Founds in metals and

their alloys
http://localhost/var/www/apps/conversion/tmp/scratch_9/New%20Folder/C02METAL.MOV


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Metallic Bonding General Characteristics

Bonding energy 25-200 Kcal/mol

Nondirectional Bond-strength of bond is equal in

all directions

Good electrical conductivity-cloud electron are

free to move to conduct electricity

Ductile, opaque

Examples Na 26 Kcal/mol, Al 74 Kcal/mol, Cu 81Kcal/mol

It involves the delocalized sharing of free

electrons among a lattice of metal atoms.


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Secondary Bonding

Van der Waals Bonding Weak secondary bond (< 10 Kcal/mol)

Often bonding force between molecules

Example- PVC can be deformed by breaking Van

der Waals bonds between molecules

Hydrogen Bonding

Special type of secondary bond between somemolecules containing H

Examplebonds between molecules of water


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molecules

molecule is considered the smallest particle of

a pure chemical substance that still retains itscomposition and chemical properties.

Most common molecules are bound together

by strong covalent bonds

i.e F2, O2, H2(diatomic molecules) or H2O, CO2(host of compounds)

The smallest molecule is the hydrogenmolecule


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Ceramics

(Ionic & covalent bonding):

Metals

(Metallic bonding):

Polymers

(Covalent & Secondary):

Large bond energy

large Tm

large E

small aVariable bond energy

moderate Tm

moderate Emoderate a

Directional PropertiesSecondary bonding dominates

small T

small E

large a

SUMMARY: PRIMARY BONDS


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TypeIonic

Covalent

Metallic

Secondary

Bond EnergyLarge!

Variablelarge-Diamondsmall-Bismuth

Variablelarge-Tungstensmall-Mercury

smallest

CommentsNondirectional (ceramics)

Directionalsemiconductors, ceramics

polymer chains)

Nondirectional (metals)

Directionalinter-chain (polymer)

inter-molecular

SUMMARY: BONDING

Atomic Structure(2008) (Chapter 1)

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