APSC 278 Lecture Notes - Lecture 1: Thermal Expansion, Thermal Energy, The Gap Band
Document Summary
Aspc 278 course notes: bonding and properties. Materials are compared in this respect: properties are controlled by: Properties controlled by bonding: melting temperature, density, thermal and electrical conductivity, coefficient of thermal expansion, stiffness. Bond energy (a measure of potential energy or energy needed to break the bond) diagram: this is net energy (between the replusive and attractive curves) is related inter-atomic separation. Equilibrium separation is at e = 0. Replusive force between atoms when they are extremely close. The minimum of the curve is the bonding energy. Types of bonds: primary bond (stronger): ionic, covalent, metallic. Ionic bond (non-directional) transfer of valance electrons between atoms. This bond is the most stable at the minimum of the net energy curve. % ionic character is based on the electronegativity. Covalent bond (directional; molecules form at preferred orientations) - sharing electrons between atoms. Metallic bond free valance electrons glue the ion core (positive) together in a (cid:862)sea of ele(cid:272)tro(cid:374)s(cid:863)
