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Homework Chapter 8
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What is the difference between an amorphous solid and a crystalline solid?
A crystalline solid has a repeating geometric arrangement of order
whereas an amorphous solid lacks this property.
Using circles, draw regular two-dimensional arrangements that
demonstrate low packing efficiency and high packing efficiency.
The packing efficiency is the fraction of the unit cell actually engaged by the atoms. It
must always be less than 100% since it is impossible to pack spheres without having
some empty space between them.
Packing Efficiency. = (area of circle) / (area of unit cell)
For a square lattice as shown, the coordination number is 4 (the number of circles
touching any individual). The coordination geometry is square, as shown below.
Two-dimensional arrangement that demonstrate low packing efficiency:
Two-dimensional arrangement that demonstrate the high packing efficiency.
The larger coordination number and greater packing efficiency suggest that this
would be more stable lattice than the square one.
Iridium forms a face-centered cubic lattice, and an iridium atom is 271.4
pm in diameter. Calculate the density of iridium.
The radius of iridium atom= r = 271.4 pm / 2
= 135.7 pm
=135.7 x 10-10 cm
For a FCC lattice
r = √2 *a /4
Where 'a' is the length of the edge.
Hence 135.7 x 10-10 cm = √2 *a/4
a = 383.87 x 10-10 cm
The density of the solid will be = N *M / Nm * a3
N = number of atoms present in the FCC unit cell = 4
Nm = Avogadro number
Therefore density of iridium = 4 * 192.2 g/mol / 6.023 x1023 * (383.87 x 1010
=22.57 g /cm3
Manganese has a body-centered cubic unit cell and has a density of 7.88
g/cm3. From this information, determine the length of the edge of the
Atomic mass (m) of Mn atom is 54.9gmol-1
The number of atoms in BCC crystal lattice, Z=2 atoms
We find the density of molybdenum
7.88 = 𝑎3 6.023∗1023
𝑎3 = 7.88∗6.023∗1023
𝑎 = (23.1 ∗ 10−24 𝑐𝑚)3
𝑎 = 481 ∗ 10−10 𝑐𝑚
𝑎 = 481𝑝𝑚
The length is 481pm
What are the four types of intermolecular forces? Rank them based on
Ionic bonds > Hydrogen bonding > Van der Waals dipole-dipole interactions >
Van der Waals dispersion forces.
What is the relationship between polarizability and dispersion forces?
Dispersion forces are associated to the naturally occurring likelihoods of
having the electron spreading momentarily uneven in two atoms while
Polarizability refers to the weakness of a molecule to having its electron
distribution transformed by an external field.
Why are dipole-dipole forces typically stronger than dispersion forces?
Dipole-dipole interactions are founded upon “permanent” dipoles as an
object of the electron distribution within the molecule. Dispersion forces
are based on sudden dipoles. The short lifetimes of these dipoles lead to a
lesser amount of attraction than the dipole-dipole force
Which of the following compounds would be expected to form
ether), (b) CH4,
hydrogen bonds in the liquid state? (a) CH3OCH3 (dimethyl
(c) HF, (d) CH3COOH (acetic acid), (e) Br2, (f) CH3OH (methanol)
Answer: (c) HF, (d) acetic aci...