Atomic Structure(2008) (Chapter 1)
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Transcript of 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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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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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
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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