Unit 1.5 Flashcards
Ionic solids?
a lattice of positive and negative ions
What is Nacl co-ordination number?
6:6
What does that mean?
1 sodium chloride = surrounded by 6 chloride ions
face centred cubic
Face centred cubic?
no molecule in middle of cube
ions = on corners of the lattice
What is CsCl coordinaton number?
8:8
Cs = lather than the sodium ion
more chlorides can get around it
Body centred
Properties of Ionic solids?
Hard but brittle
High melting points
Giant lattice with strong electrostatic forces
soluble in water
Polar and lattice has ions
If enough force = applied, the layers slide over each other and the ions repel each other
What is their electrical conductivity?
Poor when solid
but do conduct when molten as the ions = free to move
Covalent?
Macromolecules
e.g Carbon + Silicon
They both have allotropes e.g carbon = diamond + graphite
Allotrope def?
2 different structures but made of the same element
Each carbon is?
covalently bonded to 4 atoms
tetrahedral
very high melting point ( 3600 degrees)
uniformly bonded throughout
bond lengths = the same
Properties of Diamond?
used to make drill bits - glass + diamonds
insoluble in water
doesnt conduct electricity because there is no free electrons
( no attraction to the polar molecule)
strength of the bond + the geometric structure ( 300 kj mol-1)
Graphite?
also made of carbon
3 covalent bonds
4 electron = delocalised
weak vanderwaals ( 3KJ mol-1) to break
VDW = examples of induced dipole induced dipole
Physical properties of Graphite?
Strong bonds
soft + slippery
weak between layers, strong within
forms a lubricant
good conductor of electricity
low density
large amount of space between layers
Use of Graphite?
Sports equipment
Light weight
Simple moleculer solids?
Covalent bonds within but held by weak molecular
Individually - covalent
Weak VDW
