A-MT-Ch01-Introduction-&-crystals

51022electronscm3 2 ioniccrystals

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Unformatted text preview: ss these 4 types of crystals 1. Metallic crystals Consider an atom with one loosely bound electron: o Na (11 electrons = 2 + 8 + 1 electron) o Cu (29 electrons = 2 + 8 + 18 + 1 electron) In metallic crystals, electrons become practically free The positively charged ion cores are held together by a “sea” of electrons Metallic crystals have high electrical conductivity Example: Copper, Cu o 29 protons, 29 electrons, 34 neutrons o Molar mass = (29 + 34) g / mol = 63 g / mol o Avogadro’s number = 6 × 1023 atoms / mol o Mass density of Cu = 9 g / cm3 o Atoms per cm3 = 6 × 1023 atoms / mol × (1/63) mol / g × 9 g / cm3 = = 8.5 × 1022 atoms / cm3 o Electrons per cm3 = 8.5 × 1022 electrons / cm3 2. Ionic crystals Two types of atoms with large difference in electronegativity One atom has a loosely bound electron One atom has one electron missing from a noble‐gas configuration (this is a highly electronegative atom) Transfer of the loosely bound electron to the electronegative atom occurs Chapter 1 – page 12 Thus the ionic c crystal con nsists of posi itive and neg gative ions No free electrons N Io onic crystals are insulato ors Ex xample: Sod dium chloride, NaCl o Na 1 electrons = = 2 + 8 + 1 el ectron) (11 o Cl (17 7 electrons = = 1 8 – 1 elec ctron) or o NaCl is an insulato 3. Covalent crystals s Atoms with p A partially filled d outer shells bond by sh haring electrons to fill th he outer she ells Bonds between like atom ms are...
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This note was uploaded on 04/03/2014 for the course ECSE 2210 taught by Professor Huang during the Fall '12 term at Rensselaer Polytechnic Institute.

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