Week 5 pt 3

Question 1

Oxidation States:

Answer 1

• Negative oxidation states are possible – the maximum is defined
  by the difference of the # of electrons in the free atom and a full
  octet shell.
• Stability of high oxidation state decreases down group.

Question 2

Inert pair effect:

Answer 2

The tendency of two electrons in the outermost
atomic s-orbital to remain unshared.

• i. The term inert-pair effect is often
  used in relation to the increasing
  stability of oxidation states that are
  two less than the group valency for
  the heavier elements.
• ii. The inertness of the 6s2 electron pair
  is due to a relativistic contraction
  (next slide).

Question 2

Relativistic Effects

Answer 2

• A nucleus with a large charge will cause an
  electron to have a high velocity.
• A higher velocity means an increased electron
  relativistic mass, and as a result the electrons
  will be near the nucleus more of the time.
• This contracts the radius.

Question 3

1st group of the p-block:

Answer 3

• Group Trends now become less obvious, because the
  metal/nonmetal line divides the group.
• Boron is a nonmetal, the rest of the group is metals.
• The structure of the pure solids greatly affects the
  melting point of group 13, causing there to be no
  discernable trend.

-Although there is no trend
in melting point, once the
material is melted, and
structural differences are
removed, there is a trend
in boiling point.

Question 4

Group 13: Covalent bonds

Answer 4

• Boron, a semimetal, favors covalent
  bond formation, as you might expect.
• All the other nuclei in group 13 can
  also form covalent bonds, and the
  +3 oxidation state is predominant in
  solution.
• Covalent bonds can form because
  the high charge density of the group
  13 ions, can polarize any anion to
  produce a polar covalent bond.

Question 5

Boron:

Answer 5

• Boron acts like a non-metal (all nonmetals have
  extremely complex oxygen and hydride chemistry).
• Non-metals have a tendency to form covalent bonds.
• It is mined as an oxide, either borax (Na2B4O7
  .4 H2O)
  or kernite (Na2B4O7
  .10 H2O), which differ in the
  number of hydrated water molecules.
• The structures are complex: either Borate Ion or Diborane

Question 6

Preparation and Uses of Boron:

Answer 6

• Mg metal is used to reduce boron from its oxide.
• Borosilicate glass (pyrex).
• Borax, sodium peroxoborate (cleaning)
• Boron carbide: One of the hardest substances
  known. Fibers used in bullet-proof clothing.

Question 7

Aluminum:

Answer 7

• Pure aluminum is a soft, weak metal with a low density.
• 99% aluminum alloyed with silicon and iron becomes hard and
  tough. This is the typical aluminum you see.
• Aluminum is very reactive with oxygen, but forms a protective,
  or passivation layer quite easily.