Problems are listed in approximate order of difficulty. A single dot (•) indicates straigh...

Problems are listed in approximate order of difficulty. A single dot (•) indicates straightforward problems involving just one main concept and sometimes requiring no more than substitution of numbers in the appropriate formula. Two dots (••) identify problems that are slightly more challenging and usually involve more than one concept. Three dots (•••) indicate problems that are distinctly more challenging, either because they are intrinsically difficult or involve lengthy calculations. Needless to say, these distinctions are hard to draw and are only approximate.

•• The simple estimation of atomic properties as described in Problems 1 and 2 does not always work very well. Here is a well-known example where it is fairly unsuccessful: The electron affinities of 17Cl and 35Br are 3.62 and 3.36 eV. Assuming that electron affinity varies linearly within the groups of the periodic table, what would you predict for the electron affinity of 9F? The observed value is 3.40 eV.

Problems 1–2

1. •• Because of the way that atomic properties vary smoothly along the rows and columns of the periodic table, one can often predict the properties of an element from the known properties of its neighbors. (This is how Mendeleev predicted the existence and several properties of the elements now called scandium, gallium, and germanium.) (a) The ionization energies of 20Ca and 38Sr are 6.11 eV and 5.70 eV. If one guessed that ionization energies should change linearly as one moves through a group, what would one predict for the ionization energy of 56Ba? (The observed value is 5.21 eV.) (b) Use the same argument to predict the electron affinity of 35Br, given that 17Cl has electron affinity 3.61 eV and 53I has 3.06 eV. (The observed value is 3.36 eV.) (c) Predict the radius of the 9F atom, given that 7N and 8O have radii of 0.075 and 0.065 nm. (The actual value for 9F is 0.057 nm.)

2. •• (a) The electron affinities of 26Fe and 27Co are 0.163 and 0.661 eV. Using arguments similar to those outlined in Problem 1, predict the electron affinity of 28Ni. (The observed value is 1.156 eV.) (b) In the same way, predict the boiling point of 32Ge, given that the boiling point of 14Si is 3540 K and that of 50Sn is 2876 K. (The observed value is 3107 K.) (c) Similarly, predict the melting point of 86Rn, given that those of 36Kr and 54Xe are 116 K and 161 K. (The observed value is 202 K.)