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1、材料科学基础Fundamental of MaterialsLesson two*材料科学基础1.2 Atomic bondingu.Bonding forces and energiesFN : net forceFA : attractive forceFR : repulsive forceDateDate材料科学基础材料科学基础DateDate材料科学基础材料科学基础For atomic systems:Bonding energies:DateDate材料科学基础材料科学基础DateDate材料科学基础材料科学基础u.Primary interatomic bonds1. Ionic
2、 bondingIonic bonding is always found in compounds that are composed of both metallic and nonmetallic elements, elements that are situated at the horizontal extremities of the periodic table.DateDate材料科学基础材料科学基础DateDate材料科学基础材料科学基础Interionic ForcesZ1, Z2number of electrons removed or added from the
3、atoms during the ion formatione electron chargea interionic separation distance0permittivity of free space8.8510-12C2/(Nm2) DateDate材料科学基础材料科学基础Interionic EnergiesAttractive energyRepulsive energyDateDate材料科学基础材料科学基础Example problem 2.1Example problem 2.1If the attractive force between a pair of Mg2+
4、and S2- is 1.4910- 8N and if the S2- ion has a radius of 0.184nm, calculate a value for the ionic radius of the Mg2+ ion in nanometers.SolutionSolutionDateDate材料科学基础材料科学基础2. Covalent bondingMaterials with covalent bonding are characterized by bonds that are formed by sharing of valence electrons amo
5、ng two or more atoms.DateDate材料科学基础材料科学基础3. Metallic bondingMetallic bonding occurs in solid metals. In metals in solid state, atoms are packed relatively close together in a systematic pattern or crystal structure.DateDate材料科学基础材料科学基础u.Secondary bonding（Van Der waals bonding)The driving force for s
6、econdary bonding is the attraction of the electric dipoles contained in atoms or molecules.An electric dipole moment is created when two equal and opposite charges are separated.Neutral atomEDateDate材料科学基础材料科学基础Van Der waals bondingDateDate材料科学基础材料科学基础A dipole moment is defined as the charge value m
7、ultiplied by the separation distance between positive and negative charges, orDateDate材料科学基础材料科学基础uLondon forcesIf the interactions are between two dipoles that are induced in atoms or molecules, we refer to them as London forces.1. Van der waals interactionsDateDate材料科学基础材料科学基础Debye forcesWhen an i
8、nduced dipole interacts with a molecule that has a permanent dipole moment, we refer to this interaction as a Debye interaction.DateDate材料科学基础材料科学基础Keesom forcesIf the interactions are between molecules that are permanently polarized, we refer to these as Keesom interaction.DateDate材料科学基础材料科学基础2. Se
9、condary bondingFluctuating Dipole bondsThese bonding forces arise because the asymmetrical distribution of electron charge distribution in these atoms creates electric dipoles. DateDate材料科学基础材料科学基础Permanent Dipole bondsPermanent Dipole bonds exist between adjacent polar molecules. DateDate材料科学基础材料科学
10、基础3. Mixed bondingIonic-Covalent Mixed bonding Metallic-Covalent Mixed BondingMetallic-Ionic Mixed BondingXA and XB are the electronegativities of the atoms A and B in the compoundDateDate材料科学基础材料科学基础SummaryIonic bondingPrimary atomic bonds Covalent bondingMetallic bondingPermanent dipole bonds Secondary atomic bonds Fluctuating dipole bondsDateDate材料科学基础材料科学基础Examples and DiscussionsDateDate材料科学基础材料科学基础ExerciseDateDate材料科学基础材料科学基础Thank you !2 2 DateDate材料科学基础材料科学基础
