1. You should be familiar with Coulomb’s Law. Would you be able to explain it?
2. Use Lewis symbols to show the formation of ionic bond between magnesium and
nitrogen.
3. Write an electron configuration for Co2+, the ion of calcium and the ion of nitrogen.
Co2+ : [Ar] 3d7
Ca2+: [Ar] = 1s2 2s2 2p6 3s2 3p6
N3- : [Ne] = 1s2 2s2 2p6
4. Which is larger, Mg2+ or O2-? Give a reason for your choice.
These are isoelectronic (same electron configuration), however, O2- would be larger
because it has gained two particles, whereas, Mg has lost two particles.
5. Write an equation to represent
a. the lattice energy of magnesium nitride.
Formation of gaseous ions from the solid
Mg3N2 (s) → 3 Mg2+ (g) + 2 N3- (g)
b. sublimation of rubidium
sublimation is solid to gas
Rb(s) → Rb (g)
c. dissociation of iodine gas
dissociation is splitting up the diatomic gas to atoms
½ I2 (g) → I (g)
d. electron affinity of iodine
adding an electron
I (g) + e- → I- (g)
e. ionization energy for potassium
energy to remove an electron
K (g) → K+ (g) + e-Could you use similiar equations to determine a lattice energy (if you knew the enthalpy
associated with each reaction)?
6. Briefly explain how covalent bonds form. You should be familiar with the energy(ies)
associated with the process.
7. Draw a Lewis dot structure for magnesium, silicon and phosphorous.
8. Draw possible Lewis structures for
ClO3BrF5
N2H4
ClO3- has resonance structures
SO3
9. Use bond energies to estimate ΔH for the following gas-phase reaction:
N N
+ 2H H
H
H
N
N
H
H
break N triple bond N = 945 kJ
break 2 H single bond H = 432 x 2
make N single bond N = 160
make 4 N single bond H = 391 x 4
sum bonds broken = 1809 kJ
sum bonds made = 1724 kJ
overall ∆H = 1809 – 1724 = 85 kJ
10. Can GeCl4 be Td? Can NCl5 be trigonal bipyramid? Can HCN be bent?
Yes, GeCl4 can be Td because Ge has 4 valence electrons.
NCl5 cannot exist because N cannot break the octet rule.
HCN is linear
H-C≡N:
11. For each of the following molecules/ions indicate the shape, hybridization about the
central atom and the expected bond angles.
COCl2
NSF
ICl4KrF2
2
COCl2 is triagonal planar, so C is sp hybridized with expected bond angles of 120o
NSF is bent (with S in the middle have N triple bond to S which is single bond to F, there
is a lone pair around S). The hybridization around S is sp2 (coordination number is
three). Bond angles are < 120
ICl4- is square plane (I is central atom. It is attached to the 4 Cl and surrounded by two
lone pairs). Angles will be ~90o (we are not doing hybridization for square plane)
KrF2 is linear (Kr in middle. Single bond to each F, with three lone pairs). It has
coordination number of 5.
12. Do you expect ICl2+ and ICl2- to have the same hybridization scheme?
ICl2+ (put I in the middle, surrounded by two Cl and two lone pairs) is similar to water.
Bent, 4 coordinate, sp3 hybridized.
ICl2- (put I in the middle, surrounded by two Cl and three lone pairs) is linear, 5
coordinate.
They have different hybridization schemes because they have different coordination
numbers.
13. Indicate whether the molecule is polar or non-polar. If the molecule is polar,
indicate the direction of the dipole moment. Remember, to determine overall polarity,
think about the symmetry (or lack thereof).
C2H4
H
H
non-polar
COCl2
H
H
HCN
SF6
O
Cl
polar
NO2
F
Cl
H
N
polar
F
F
S
F
F
F
non-polar
O
N
O
polar (bent)