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2 Estrutura Atomica e Ligacao 2 Estrutura Atomica e Ligacao InteratomicaInteratomica
IntroducaoIntroducaoPropriedades dependem Propriedades dependem dos arranjos dos arranjos geometricos dos atomos geometricos dos atomos e das interacoes (entre e das interacoes (entre atomos ou moleculas)atomos ou moleculas)
orbital electrons: n = principal quantum number
n=3 2 1
Nucleo: Z = # protons
N = # neutrons
Massa Atomica A ≈ Z + N
Atomo de Bohr
22
• have discrete energy states• tend to occupy lowest available energy state.
Incr
easi
ng e
nerg
y
n=1
n=2
n=3
n=4
1s2s
3s2p
3p
4s4p
3d
Electrons...ELECTRON ENERGY STATESELECTRON ENERGY STATES
33
He
Ne
Ar
Kr
Xe
Rn
inert
gases
accept
1e
accept
2e
giv
e u
p 1e
giv
e u
p 2e
giv
e u
p 3e
F Li Be
Metal
Nonmetal
Intermediate
H
Na Cl
Br
I
At
O
S Mg
Ca
Sr
Ba
Ra
K
Rb
Cs
Fr
Sc
Y
Se
Te
Po
• Columns: Similar Valence Structure
Tabela PeriodicaTabela Periodica
44
Ligacao AtomicaLigacao Atomica Forcas e Energias de LigacaoForcas e Energias de Ligacao
55
Energia de LigacaoEnergia de Ligacao
Resistencia MecanicaResistencia Mecanica Temperatura de FusaoTemperatura de Fusao Modulo de ElasticidadeModulo de Elasticidade Coeficiente de Expansao termicaCoeficiente de Expansao termica
Distancia de EquilibrioDistancia de Equilibrio Energia Total e minimaEnergia Total e minima Forcas de Atracao e repulsao sao Forcas de Atracao e repulsao sao
nulasnulas
66
Ligacoes AtomicasLigacoes Atomicas
IonicaIonica CovalenteCovalente MetalicaMetalica Van der WaalsVan der Waals
MoleculasMoleculas
77
Ligacao Ionica Ligacao Ionica
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
• Ocorre entre ions + e – • E necessario transferencia de eletrons
• Exemplo: NaCl
+_
88
• Requires shared electrons• Example: CH4
C: has 4 valence e, needs 4 more
H: has 1 valence e, needs 1 more
Electronegativities are comparable.
shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
COVALENT BONDINGCOVALENT BONDING
99
Arises from interaction between dipoles
• Permanent dipoles-molecule induced
• Fluctuating dipoles
+ - secondary bonding + -
H Cl H Clsecondary bonding
secondary bonding
HH HH
H2 H2
secondary bonding
ex: liquid H2asymmetric electron clouds
+ - + -secondary bonding
-general case:
-ex: liquid HCl
-ex: polymer
SECONDARY BONDINGSECONDARY BONDING
1010
• Arises from a sea of donated valence electrons (1, 2, or 3 from each atom).
• Primary bond for metals and their alloys
+ + +
+ + +
+ + +
METALLIC BONDINGMETALLIC BONDING
1111
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large!
Variablelarge-Diamondsmall-Bismuth
Variablelarge-Tungstensmall-Mercury
smallest
Comments
Nondirectional (ceramics)
Directional(semiconductors, ceramics
polymer chains)
Nondirectional (metals)
Directionalinter-chain (polymer)
inter-molecular
SUMMARY: BONDINGSUMMARY: BONDING
1212
• Bond length, r
• Bond energy, Eo
F F
r
• Melting Temperature, Tm
Eo=
“bond energy”
Energy (r)
ro r
unstretched length
r
larger Tm
smaller Tm
Energy (r)
ro
Tm is larger if Eo is larger.
PROPERTIES FROM BONDING: PROPERTIES FROM BONDING: TTMM
1313
• Elastic modulus, E
• E ~ curvature at ro
cross sectional area Ao
L
length, Lo
F
undeformed
deformed
L F Ao
= E Lo
Elastic modulus
r
larger Elastic Modulus
smaller Elastic Modulus
Energy
ro unstretched length
E is larger if Eo is larger.
PROPERTIES FROM BONDING: PROPERTIES FROM BONDING: EE
1414
• Coefficient of thermal expansion,
• ~ symmetry at ro
is larger if Eo is smaller.
L
length, Lo
unheated, T1
heated, T2
= (T2-T1) L Lo
coeff. thermal expansion
r
smaller
larger
Energy
ro
PROPERTIES FROM BONDING: PROPERTIES FROM BONDING:
1515
Ceramics(Ionic & covalent bonding):
Metals(Metallic bonding):
Polymers(Covalent & Secondary):
secondary bonding
Large bond energylarge Tm
large Esmall
Variable bond energymoderate Tm
moderate Emoderate
Directional PropertiesSecondary bonding dominates
small Tsmall Elarge
SUMMARY: PRIMARY SUMMARY: PRIMARY BONDSBONDS