Problem 48
A The following are isoelectronic species: \(\mathrm{Cl}^{-}, \mathrm{K}^{+},\) and \(\mathrm{Ca}^{2+} .\) Rank them in order of increasing (a) size, (b) ionization energy, and (c) electron attachment enthalpy.
Problem 49
Compare the elements \(\mathrm{Na}, \mathrm{B}, \mathrm{Al},\) and \(\mathrm{C}\) with regard to the following properties: (a) Which has the largest atomic radius? (b) Which has the most negative electron attachment enthalpy? (c) Place the elements in order of increasing ionization energy.
Problem 50
Two elements in the second transition series (Y through Cd) have four unpaired electrons in their 3+ ions. What elements fit this description?
Problem 53
Nickel(II) formate \(\left[\mathrm{Ni}\left(\mathrm{HCO}_{2}\right)_{2}\right]\) is widely used as a catalyst precursor and to make metallic nickel. It can be prepared in the general chemistry laboratory by treating nickel(II) acetate with formic acid (HCO,H). \(\mathrm{Ni}\left(\mathrm{CH}_{3} \mathrm{CO}_{2}\right)_{2}(\mathrm{aq})+2 \mathrm{HCO}_{2} \mathrm{H}(\mathrm{aq}) \rightarrow\) $$ \mathrm{Ni}\left(\mathrm{HCO}_{2}\right)_{2}(\mathrm{aq})+2 \mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}(\mathrm{aq}) $$ Green crystalline \(\mathrm{Ni}\left(\mathrm{HCO}_{2}\right)_{2}\) is precipitated after adding ethanol to the solution. (a) What is the theoretical yield of nickel(II) formate from 0.500 g of nickel(II) acetate and excess formic acid? (b) Is nickel(II) formate paramagnetic or diamagnetic? If it is paramagnetic, how many unpaired electrons would you expect? (c) If nickel(II) formate is heated to \(300^{\circ} \mathrm{C}\) in the absence of air for 30 minutes, the salt decomposes to form pure nickel powder. What mass of nickel powder should be produced by heating 253 mg of nickel(II) formate? Are nickel atoms paramagnetic?
Problem 55
Why is the radius of \(\mathrm{Li}^{+}\) so much smaller than the radius of Li? Why is the radius of \(\mathrm{F}^{-}\) so much larger than the radius of F?
Problem 56
Which ions in the following list are not likely to be found in chemical compounds: \(\mathrm{K}^{2+}, \mathrm{Cs}^{+}, \mathrm{Al}^{4+}, \mathrm{F}^{2-},\) and \(\mathrm{Se}^{2-} ?\) Explain briefly.
Problem 58
The ionization of the hydrogen atom can be calculated from Bohr's equation for the electron energy. $$ E=-(N R h c)\left(Z^{2} / n^{2}\right) $$ where \(N R h c=1312 \mathrm{kJ} / \mathrm{mol}\) and \(Z\) is the atomic number. Let us use this approach to calculate a possible ionization energy for helium. First, assume the electrons of the He experience the full \(2+\) nuclear charge. This gives us the upper limit for the ionization energy. Next, assume one electron of He completely screens the nuclear charge from the other electrons, so \(Z=1 .\) This gives us a lower limit to the ionization energy. Compare these calculated values for the upper and lower limits to the experimental value of \(2372.3 \mathrm{kJ} / \mathrm{mol} .\) What does this tell us about the ability of one electron to screen the nuclear charge?
Problem 61
Write electron configurations to show the first two ionization processes for potassium. Explain why the second ionization energy is much greater than the first.
Problem 62
What is the trend in ionization energy when proceeding down a group in the periodic table. Rationalize this trend.
Problem 63
(a) Explain why the sizes of atoms change when proceeding across a period of the periodic table. (b) Explain why the sizes of transition metal atoms change very little across a period.
