enriched chem Flashcards
two types of solids
amorphous and crystalline
define amorphous solid
local ordering and lack any long range 3D order and structure, solutions that have been frozen in place before reaching a high ordered structure (ex glass)
define crystalline solid
long range repeating 3D structures. Most elements and solid compounds form crystalline solids
classifications of crystalline solids
atomic solids = only atoms in crystal structure (ex diamond)
ionic solids = made from ions (ex salt)
molecular solids = molecules dispersed through crystal structure (ex ice)
definition of crystal lattice
molecules or ions are in a regular 3D pattern called a crystal lattice made up of repeating sub units (unit cells)
name all crystal systems (unit cells)
cubic tetragonal orthorhombic monoclinic hexagonal rhombohedral triclinic
name the bravais lattices for cubic crystal system
simple cubic = atoms at corners of cube (total = 1 atom)
body centred cubic = corners and one in centre (total = 2 atoms)
face centred cubic = corners and six faces of cube (total = 4 atoms)
how are layers placed in a closest packed structure (1st + 2nd)
on top of one another in an offset pattern, 2nd layer placed in indentations of first
state the packing efficiency for the cubic bravais lattices
simple = least efficiently packed 52% body = 68% face = most efficiently packed 74% (closest packed structure for a collection of spherical objects)
characteristics of crystal systems
cubic Y = 90, B = 90, A = 90, a, b=a, c=a
tetragonal Y = 90, B = 90, A = 90, a, b=a, c
orthorhombic Y = 90, B = 90, A = 90, a, b, c
monoclinic Y, B = 90, A = 90, a, b, c
hexagonal Y = 120, B = 90, A = 90, a, b=a, c
rhombohedral A, A, A, a, b=a, c=a
triclinic Y, B, A, a, b, c
describe placement of 3rd layers
3rd layer determines type of crystal system
placed directly above first layer = ABA system which forms hexagonal unit cells (ex of hexagonal closest packed structure)
placed not above first or second layer = ABC system which forms face centred cubic cells (ex of cubic closest packed structure)
describe allotropes of carbon
graphite, diamond and buckminsterfullerenes
define allotropy
the existence of different forms of the same element
define allotrope
distinct forms of an element generally in the same phase
characteristics of buckminsterfullerenes
discovered in 1985, they are molecules comprised of 60 carbon atoms and are shaped like soccer balls
characteristics of diamond
extremely hard, each carbon atoms is covalently bonded to four other carbon atoms in a tetrahedral structure which imparts great rigidity. no delocalized electrons so it doesn’t conduct electricity, less thermodynamically stable than graphite but forms under higher conditions of pressure
describe allotropes of sulfur
sulfur can be found in minerals, pyrite FeS, PbS, cinnabar, HgS, has more allotropes than any other element
in solid state = rhombic sulfur and monoclinic sulfur, both are made from the same s8 crown shaped ring
in gas state = sulfur in the s s2 s4 s8 forms are observed under different conditions of temperature and pressure
in liquid state = long polymeric chains of sulfur exist
characteristics of graphite
soft and slippery material, ideal for writing, carbon atoms bonded together in hexagonal sheets, layers interact weakly and slide across each other allowing graphite to be deposited, graphite conducts electricity, each carbon is covalently bonded to three other carbon atoms per layer leaving one delocalized electron per carbon
characteristics of rhombic sulfur
most stable form of sulfur, made up of cyclic s8 molecules, heating rhombic sulfur to 120 and slow cooling it gives monoclinic sulfur
characteristics of monoclinic sulfur
below 96 monoclinic sulfur converts back to rhombic
