CHEM 1300 Lecture Notes - Lecture 19: Dopant, Fluorite, Coordination Number
26 Jun 2018
School
Department
Course
Professor
Lecture 19 -Body Centered Cubic, Closed Packed Models, Packing Types
●Body centered cubic – BCC
oLength edges (4/√3)(r)
o2 atoms/unit cell
oCentre atom fully inside cell
oCoordination number 8
oPacking efficiency 68% (intermediate of Simple and FCC)
oCommonly seen in:
▪Alkali Metals
▪Fe
▪Groups 5+6
Packing
●2 types of packing
oHexagonal Closed Packed (HCP)
oCubic Closed Packed (CCP)
●HCP:
oCoordination Number 12
oPacking Efficiency 74%
o1st layer aligns in a row
▪Rows are staggered (shift one up/down and one right/left)
▪Accounts for trigonal shaped holes
o2nd layer falls into place over 1st layer holes
▪Forms 2 layers of holes
▪ABABAB Layering
o3rd layer falls into holes from 2nd layer
▪Alignment is equal to first layer (sits directly on stop)
▪E.g. Mg, Zn
●CCP (packing for ionic compounds)
oCoordination Number 12
oPacking Efficiency 74%
oFIRST TWO layers are HCP
▪3rd layer is an offset from both 1st and 2nd layer
▪Covers holes from 1st and 2nd layer
▪ABCABCABC layering
▪E.g. Ag, Au, Ar, Ni
oIn ionic solids:
▪Usually classified by an anion in lattice position
▪Cation in void space
▪Overall charge of unit cell is zero
▪FCC – Halides (group 1 – omitting cesium)
●Oxides (group 2)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Lecture 19 -body centered cubic, closed packed models, packing types. Body centered cubic bcc: length edges (4/ 3)(r, 2 atoms/unit cell, centre atom fully inside cell, coordination number 8, packing efficiency 68% (intermediate of simple and fcc, commonly seen in, alkali metals, fe, groups 5+6. 2 types of packing: hexagonal closed packed (hcp, cubic closed packed (ccp) Ccp (packing for ionic compounds: coordination number 12, packing efficiency 74, first two layers are hcp, 3rd layer is an offset from both 1st and 2nd layer, covers holes from 1st and 2nd layer, abcabcabc layering, e. g. Ag, au, ar, ni: in ionic solids, usually classified by an anion in lattice position, cation in void space, overall charge of unit cell is zero, fcc halides (group 1 omitting cesium) Oxides (group 2: bcc halides of cesium (cscl, fluorite (naf) cations are fcc, anions simple, change in lattice site will change classification of crystals.
