Download for the quiz on 6 mar

Suggested problems for quiz 6 March
19.21 Arrange the following elements in order of increasing ionization energy:
a. P
b. K c. Al d. F
19.27 Which element in each of the following pairs has more nonmetallic character?
a. S or Te
b. Cl or P
c. Bi or Br
19.43 Explain why the properties of boron differ so markedly from the properties of the
other group 3A elements.
19.98 Explain why acid strength increases in the order
HClO < HClO2 < HClO3 < HClO4
19.21 Ionization energy decreases going down the periodic table. It also increases going
to the right – as Zeff increases, the electrons are held more tightly.
Starting with the lowest… K < Al < P < F
19.27 Which is closer to the “nonmetals” part of the periodic table?
a. S
b. Cl c. Br
19.43 Of the group 3A elements, boron is the only one on the “nonmetals” side of the
line. The rest of the group 3A elements participate in ionic bonding, and form ions.
Boron, on the other hand, forms compounds through sharing of electrons in covalent
bonds.
19.98 In order to have a stronger acid, you want to make the O-H bond weaker. (There
is a figure on p.646 in Ch. 15 which may help with this…) If you increase the number of
oxygens in the molecule, you are drawing more electron density away from the Cl by
bonding it to more (greater number of) electronegative O atoms. By doing so, you wind
up with a partial positive charge on the Cl in HClO4, which draws more electron density
away from the O-H bond (the acidic region of the molecule), which weakens that bond –
makes deprotonation easier. Deprotonation is easier when your conjugate base ends up
with less electron density/charge, and the presence of the additional O’s in the
perchlorate anion helps draw that charge away. Thus, perchloric acid is the strongest
acid of the group.
**In this chapter, I’ve noticed that our book has more “memorization” based questions
and fewer concept-based questions. I’m going to give you a few other concept-based
questions (below) from other sources, because I really don’t need you to memorize the
names of 20 different phosphorus compounds… see more questions below. Bottom
line… understand the periodic table trends within rows and groups.
1. How does Zeff influence atomic size and IE across a row of elements?
2. How are bond energy, bond length, and reactivity related for similar compounds?
3. The compound NF3 is quite stable, but NCl3 is very unstable (it was first synthesized
by P.L Dulong, who lost three fingers and an eye studying its properties). The
compounds NBr3 and NI3 are very rare. Account for the instability of these halides of N.
1. Going to the right across a row, Zeff increases due to the presence of more protons in
the nucleus, without additional shielding (no extra layers of electrons). More protons =
more positive charge = outer electrons pulled in more tightly. Thus, it would follow that
as you go to the right in a row, in general, atomic radius decreases. Similarly, as the
outermost electrons are held more tightly on the right side of a row (due to the increased
number of protons in the nucleus on the right compared to the left), IE tends to be higher
on the right, if you’re comparing within the same row.
2. Longer bonds contain less energy, as a general rule; shorter bonds are stronger
bonds. Therefore, longer bonds are easier to break, and they are also therefore more
reactive.
3. N is small, being in row 2 of the periodic table. F is also quite small. Br, I, and Cl are
larger halogens, though. It becomes more challenging to fit these larger halogens
around the small N – that’s why the halides containing the larger halogens are less
stable.