In Fig. 1.16, identify the trends in the first ionization energies of the elements in (a) descending group 1 , (b) descending group 13, (c) crossing the first row of the $d$-block, (d) crossing the row of elements from B to Ne, (e) going from Xe to $\mathrm{Cs}$, and (f) going from $\mathrm{P}$ to $\mathrm{S}$. Rationalize each of the trends you have described.

What explanation can you give for the decrease in solubility of the alkaline earth metal sulfates in the sequence $\mathrm{CaSO}_4>\mathrm{SrSO}_4>\mathrm{BaSO}_4$ ?

(a) Draw possible stereoisomers for the trigonal bipyramidal $\left[\mathrm{SiF}_3 \mathrm{Me}_2\right]^{-}$anion $\left(\mathrm{Me}=\mathrm{CH}_3\right)$. An X-ray diffraction study of a salt of $\left[\mathrm{SiF}_3 \mathrm{Me}_2\right]^{-}$ shows that two $\mathrm{F}$ atoms occupy axial sites. Suggest why this stereoisomer is preferred over the other possible structures that you have drawn. (b) Account for the fact that members of the series of complexes $\left[\mathrm{PtCl}_4\right]^{2-},\left[\mathrm{PtCl}_3\left(\mathrm{PMe}_3\right)\right]^{-}$, $\left[\mathrm{PtCl}_2\left(\mathrm{PMe}_3\right)_2\right]$ and $\left[\mathrm{PtCl}\left(\mathrm{PMe}_3\right)_3\right]^{+}$do not possess the same number of stereoisomers.

(a) Construct an MO diagram for the formation of $\mathrm{O}_2$; use only the valence orbitals of the oxygen atoms. (b) Use the diagram to rationalize the following trend in $\mathrm{O}-\mathrm{O}$ bond distances: $\mathrm{O}_2, 121 \mathrm{pm} ;\left[\mathrm{O}_2\right]^{+}, 112 \mathrm{pm}$; $\left[\mathrm{O}_2\right]^{-}, 134 \mathrm{pm} ;\left[\mathrm{O}_2\right]^{2-}, 149 \mathrm{pm}$. (c) Which of these species are paramagnetic?

Using VB theory and the Lewis structure model, determine the bond order in (a) $\mathrm{H}_2$, (b) $\mathrm{Na}_2$, (c) $\mathrm{S}_2$, (d) $\mathrm{N}_2$ and (e) $\mathrm{Cl}_2$. Is there any ambiguity with finding the bond orders by this method?

Calculate the enthalpy of combustion of methane, if the standard enthalpies of formation of methane, carbon dioxide, and water are $-74.85$,$−393.5$ and $−286 \text{ kJ/mol}$, respectively.

The first four ionization energies of an atom $\mathrm{X}$ are 403 , 2633,3900 and $5080 \mathrm{~kJ} \mathrm{~mol}^{-1}$. Suggest to what periodic group $\mathrm{X}$ belongs and give reasons for your choice.

(a) Write down an equation that defines the process to which the value of $I E_4$ of $\mathrm{S} n$ refers. Is this process exothermic or endothermic? (b) To what overall process does a value of $\left(I E_1+I E_2+I E_3\right)$ for $\mathrm{Al}$ refer?

An electron has the quantum numbers $n=4, l=1, m_l=0$ and $m_x=+\frac{1}{2}$. Is the electron in a $4 s, 4 p$ or $4 d$ atomic orbital?

Draw energy level diagrams to show the ground state electronic configurations of only the valence electrons in an atom of (a) $\mathrm{F}$, (b) $\mathrm{Al}$ and (c) $\mathrm{Mg}$.

An electron has the quantum numbers $n=4, l=1, m_l=0$ and $m_x=+\frac{1}{2}$. Is the electron in a $4 s, 4 p$ or $4 d$ atomic orbital?

Using the list of naturally occurring isotopes in Appendix 5, determine the number of electrons, protons and neutrons present in an atom of each isotope of (a) $\mathrm{Al}$, (b) $\mathrm{Br}$ and (c) Fe, and give appropriate notation to show these data for each isotope.

Figure shows the emission spectrum of sodium. Low-pressure sodium street lamps depend upon this bright yellow emission from sodium atoms excited by an electrical discharge. Figure shows a simple spectrum (see figure caption), but the National Institute of Standards and Technology (NIST) atomic spectra database lists 5888 lines in the emission spectrum of sodium. Suggest three reasons why no other lines are visible in Fig. (b) The wavelengths of the yellow lines in Fig. are close to $589 \mathrm{~nm}$. To what frequency does this correspond? (c) Give a general explanation of how a series of spectral lines such as those in Fig. arises.

Using the list of naturally occurring isotopes in Appendix 5, determine the number of electrons, protons and neutrons present in an atom of each isotope of (a) $\mathrm{Al}$, (b) $\mathrm{Br}$ and (c) Fe, and give appropriate notation to show these data for each isotope.