Atomic solids; molecular solids; ionic solids Flashcards
What are the intermolecular forces which hold atomic solids?
dispersion forces (London forces)
- weak forces
- arise from instantaneous dipole at one atom inducing dipole in its neighbor
(thus get synchronized motion of electron in adjacent atoms)
what are the examples of atomic solids?
G18
Ar crystallizes at very low T in a cubic closest packed structure
What are the intermolecular forces acting on molecular solids?
dipole-dipole, dispersion, H-bonding
- still relatively weak
what is the effect of the varied intermolecular forces acting on molecular solids?
wide range of physical properties
what are the lattice points of a molecular solid occupied by?
molecules
what does methane crystallize into?
in face centered cubic structure
why do molecular solids have lower mp than ionic, network covalent and metallic solids?
due to their weak intermolecular forces
true or false; the particles of ionic solids have charges
true
true or false; the inter-particle forces are much greater in ionic solids
true
why is the inter-particle forces in ionic solids much greater than molecular solids?
they maximize their attraction; cations are surrounded by as many anions as possible and vice versa
where do the smaller ions lie in the packing of ionic solids?
in the spaces (holes) formed by close packed larger ions
true or false; the unit cell has the same cation: anion ratio as the empirical formula
true
what is the most common ratio that crystal structures adopt?
1:1 cation:anion ratio cubic closest packing eg. NaCl and ZnS
In NaCl structure; what type of array does the Cl- ions make?
cubic closed packed
in NaCl where do the smaller sodium ions fit into?
the holes or spaces within the lattice
What type of arrangement does the NaCl adopt?
face centred
how many Cl- ions surround each Na+ ions? (vice versa) CN
6
what holes are the Na+ ions filling?
octahedral of the fcc lattice of the Cl- ions
How many Cl- ions in the NaCl unit cell?
4
how many Na+ ions in the NaCl unit cell
4
where is the NaCl structure mostly found in?
G1 halides and hydrides
G2 oxides and sulfides
most AgX
What is Zinc blende?
ZnS
What type of array is ZnS packed?
cubic close packed array of S(2-) ions with the cations Zn(2+)
what holes are the Zn(2+) occupying in the S(2-) lattice? (vice versa)
half of the tetrahedral holes
how many S(2-) surround each Zn(2+) ions (vice versa) CN
4
how many Zn(2+) ions in a ZnS unit cell?
4
how many S(2-) ion in a ZnS unit cell
4
what is the ion ratio of ZnS
1:1
true or false; only 4 of 8 tetrahedral holes in the fcc unit cell are filled by Zn(2+)
true
What other compounds adopt the ZnS structure
Cu(i) halides, CdS, AgI
What determines the type of structure other compounds will adopt
the sizes of the cation:anion ratio
true or false; the space available in an octahedral hole is much larger than in a tetrahedral hole in a cubic close packed array
true
what radius ratio is needed for cation:anion for ZnS to be adopted?
> 414
radius ratio cation:anion for NaCl structure
> 414 but no more than 732 (between 414 and 732)
cation: anion radius ratio for CsCl structure; interpenetrating cubic arrays (most stable)
<732
what is anion to cation ratio of CsCl
0.92
what array forms the CsCl structure
cubic array of Cl- ion with Cs+ ions
which holes are Cs+ ions placed in
cubic holes
what is the lattice of CsCl constructed form?
cubic Cl-
what is the CN (coordination number) of cation and anion of CsCl
8
true or false; anions are generally larger than cations
true
