CHEM104
QUIZ 1
Spring 2010
INSTRUCTIONS:
- This Quiz is due Monday Jan. 24, to be handed in during class
- There is no time constraint on this quiz
- For this quiz, do not use your text, but you may consult a Periodic Table.
- Be sure to make a photocopy, or record a copy of your work that you’ll need for
…
What happens next:
- Monday after class I will post the answers to Quiz 1.
- Check my answers against your, identify what mistakes you made and why
- Hand in the corrected Quiz 1 by Tuesday 5PM.
1. For the following pairs of items, say:
(a) in what way(s) they are similar and (b) in what way(s) they differ.
i.
a metal and an ionic solid
(a) way(s) they are similar:
a. both have a crystal structure of repeating units
(b) in what way(s) they differ
a. a metal is composed of only one atom, whereas an ionic solid must have at
least two different elements as ions.
b. Many properties differ: malleability, electric conductivity, solubility
c. Metallic bonds are covalent while ionic bonds are …ionic.
ii.
a metal and a network solid
(a) way(s) they are similar:
a. both have a crystal structure of repeating units
b. both can be composed of a single element
(b) in what way(s) they differ
a. a metal lattice is (usually) a closed packed one, ccp or hcp, or bcc. A network solid
has an open lattice, not so closed packed.
b. Many properties differ: malleability, hardness …
iii.
an ionic solid and a molecular solid
(a) way(s) they are similar:
a. both have a crystal structure of repeating units
(b) in what way(s) they differ
a. The molecular solid has shorter stronger bonds (covalent) between atoms of
the molecule and longer weaker bonds between molecules. All the bonds in
ionic solids are (pretty much) the same.
b. Many properties differ: melting point, solubility.
c. The materials behave differently when their solid structure is destroyed.
Ionic materials give separated (solvated) ions; molecular solids retain the
molecules when melted or dissolved.
iv.
NaCl and CsCl
(a) way(s) they are similar:
a. both are ionic solids
b. both have a 1:1 composition
(b) in what way(s) they differ
a. NaCl is a FCC structure while CsCl is a simple cubic lattice.
2. What is the empirical formula of the unit cell shown below?
(explain your work)
The grey balls are Ca(2+) and the lime balls are F-.
There are 8 F ions (yellow green) inside and
(8 x 1/8) = 1 Ca ions (grey) at the vertices plus
(6 x ½) = 3 Ca at the face centers
so the ratio is 4 Ca” 8 F which is CaF2 (or the mineral Fluorite)
3. The Mars Rover brought back a “mystery metal”. Lab tests showed that it
crystallizes in a fcc cubic lattice with cell edge a = 508.42 pm (data from X-ray
diffraction) and its density is 11.724 g cm-3 (from density experiments).
What is the atomic weight of this metal? Could it be one known on Earth?
I use the formula:
Rearranged:
Density = Z x at.wt./ (A x a3)
Density x (A x a3) / Z = atomic weight
(11.724 g cm-3) x (6.022 ^23 atom/mol) x (5.0842 ^-8 cm)3 /4 = 231. 97 g/mol
So the Martian metal could be Thorium (Th) At. Wt. 232.