2 Estrutura Atomica e Ligacao Interatomica - PowerPoint PPT Presentation

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2 Estrutura Atomica e Ligacao Interatomica

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2 Estrutura Atomica e Ligacao Interatomica Introducao Propriedades dependem dos arranjos geometricos dos atomos e das interacoes (entre atomos ou moleculas) – PowerPoint PPT presentation

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Title: 2 Estrutura Atomica e Ligacao Interatomica


1
2 Estrutura Atomica e Ligacao Interatomica
  • Introducao
  • Propriedades dependem dos arranjos geometricos
    dos atomos e das interacoes (entre atomos ou
    moleculas)

Atomo de Bohr
Nucleo Z protons
N neutrons
Massa Atomica A Z N
2
ELECTRON ENERGY STATES
Electrons...
have discrete energy states tend to occupy
lowest available energy state.
3
Tabela Periodica
Columns Similar Valence Structure
4
Ligacao Atomica
  • Forcas e Energias de Ligacao

5
Energia de Ligacao
  • Resistencia Mecanica
  • Temperatura de Fusao
  • Modulo de Elasticidade
  • Coeficiente de Expansao termica

Distancia de Equilibrio
  • Energia Total e minima
  • Forcas de Atracao e repulsao sao nulas

6
Ligacoes Atomicas
  • Ionica
  • Covalente
  • Metalica
  • Van der Waals

Moleculas
7
Ligacao Ionica
  • Ocorre entre ions e

E necessario transferencia de eletrons
Exemplo NaCl
_

8
COVALENT BONDING
Requires shared electrons
Example CH4
C has 4 valence e, needs 4 more
H has 1 valence e, needs 1 more
Electronegativities are comparable.
9
SECONDARY BONDING
Arises from interaction between dipoles
Fluctuating dipoles
Permanent dipoles-molecule induced
-general case
-ex liquid HCl
-ex polymer
10
METALLIC BONDING
Arises from a sea of donated valence
electrons (1, 2, or 3 from each atom).
Primary bond for metals and their alloys
11
SUMMARY BONDING
Type
Bond Energy
Comments
Ionic
Large!
Nondirectional (ceramics)
Variable
Directional
Covalent
large-Diamond
(semiconductors, ceramics
small-Bismuth
polymer chains)
Variable
Metallic
large-Tungsten
Nondirectional (metals)
small-Mercury
Directional
inter-chain (polymer)
Secondary
smallest
inter-molecular
12
PROPERTIES FROM BONDING TM
Bond length, r
Melting Temperature, Tm
Bond energy, Eo
Tm is larger if Eo is larger.
13
PROPERTIES FROM BONDING E
Elastic modulus, E
E curvature at ro
E is larger if Eo is larger.
14
PROPERTIES FROM BONDING a
Coefficient of thermal expansion, a
a symmetry at ro
a is larger if Eo is smaller.
15
SUMMARY PRIMARY BONDS
Ceramics
Large bond energy large Tm large E small a
(Ionic covalent bonding)
Metals
Variable bond energy moderate Tm moderate
E moderate a
(Metallic bonding)
Polymers
Directional Properties Secondary bonding
dominates small T small E large a
(Covalent Secondary)
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