第2课材料化学全英文课件.ppt

材料科学基础Fundamental of Materials Science 1.2 Atomic Bonding 1.2.2 Primary interatomic bonds 1. Ionic bonding Ionic 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. 2. Covalent bonding Materials with covalent bonding are characterized by bonds that are formed by sharing of valence electrons among two or more atoms. 3. Metallic bonding Metallic bonding occurs in solid metals. In metals in solid state, atoms are packed relatively close together in a systematic pattern or crystal structure. 1.2.3 Secondary bonding （Van der Waals bonding) The driving force for secondary 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. Dispersion force (London forces) If the interactions are between two dipoles that are induced in atoms or molecules, we refer to them as London forces. 1.2.4 Mixed bonding in materials 2. Physical absorption and chemical absorption 1.2.5 Bonding and properties Some properties can be related to the force-distance and energy-distance. For example: We cannot simply predict whether or not a material will be high or low strength, ductile or brittle ,simply based on the nature of bonding! We need additional information on the atomic, microstructure, and macrostructure of the material. However, the nature of bonding does point to a trend for materials with certain types of bonding and chemical compositions. Summary Discussions Example Exercise 1.If the attractive force between a pair of Mg2+and S2- is 1.49×10-8 N and if the S2- ion has a radius of 0.184nm, calculate a value for the ionic radius of the Mg2+ ion in nanometers. Solution 2.(a) Using the ionic radii data, calculate the coulombic force of attraction betw