1 2 Estrutura Atomica e Ligacao Interatomica Introducao Introducao Propriedades dependem dos arranjos geometricos dos atomos e das interacoes (entre atomos ou moleculas) Nucleo: Z = # protons N = # neutrons Massa Atomica A Z + N Atomo de Bohr

2 have discrete energy states tend to occupy lowest available energy state. Electrons... ELECTRON ENERGY STATES

3 Columns: Similar Valence Structure Tabela Periodica

4 Ligacao Atomica Forcas e Energias de Ligacao Forcas e Energias de Ligacao

5 Energia de Ligacao Resistencia Mecanica Resistencia Mecanica Temperatura de Fusao Temperatura de Fusao Modulo de Elasticidade Modulo de Elasticidade Coeficiente de Expansao termica Coeficiente de Expansao termica Distancia de Equilibrio Energia Total e minima Energia Total e minima Forcas de Atracao e repulsao sao nulas Forcas de Atracao e repulsao sao nulas

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

7 Ligacao Ionica Ocorre entre ions + e – E necessario transferencia de eletrons Exemplo: NaCl + _

8 Requires shared electrons Example: CH 4 C: has 4 valence e, needs 4 more H: has 1 valence e, needs 1 more Electronegativities are comparable. COVALENT BONDING

9 Arises from interaction between dipoles Permanent dipoles-molecule induced Fluctuating dipoles -general case: -ex: liquid HCl -ex: polymer SECONDARY BONDING

10 Arises from a sea of donated valence electrons (1, 2, or 3 from each atom). Primary bond for metals and their alloys METALLIC BONDING

11 Type Ionic Covalent Metallic Secondary Bond Energy Large! Variable large-Diamond small-Bismuth Variable large-Tungsten small-Mercury smallest Comments Nondirectional (ceramics) Directional (semiconductors, ceramics polymer chains) Nondirectional (metals) Directional inter-chain (polymer) inter-molecular SUMMARY: BONDING

12 Bond length, r Bond energy, E o Melting Temperature, T m T m is larger if E o is larger. PROPERTIES FROM BONDING: T M

13 Elastic modulus, E E ~ curvature at r o E is larger if E o is larger. PROPERTIES FROM BONDING: E

14 Coefficient of thermal expansion, ~ symmetry at r o is larger if E o is smaller. PROPERTIES FROM BONDING: PROPERTIES FROM BONDING:

15 Ceramics (Ionic & covalent bonding): Metals (Metallic bonding): Polymers (Covalent & Secondary): Large bond energy large T m large E small Variable bond energy moderate T m moderate E moderate Directional Properties Secondary bonding dominates small T small E large SUMMARY: PRIMARY BONDS