The ionic model: notes and practice questions

Antimony (Sb) and Bismuth (Bi) are elements in group 15 of the periodic table.

(a) Antimony has two stable isotopes. 57.21% of antimony atoms contain 70 neutrons and the remainder contain 72 neutrons.

(i) Deduce the nuclear symbol of the isotope of antimony containing 72 neutrons. Use section 6 of the data booklet.

(ii) Calculate, to two decimal places, the relative atomic mass of antimony.

Bismuth(III) nitrate, $Bi(NO_3)_3$, is a common salt of bismuth.

(b) (i) The compound contains both ionic and covalent bonds. State which particles are joined by covalent bonds and which are joined by ionic bonds.

(ii) Distinguish between covalent and ionic bonding in terms of electron distribution.

(iii) State the enthalpy term that characterizes the strength of the bonding between the ions in an ionic solid.

(iv) Write an equation for the formation of aqueous bismuth(III) nitrate from solid bismuth(III) oxide and nitric acid.

(v) Calculate the volume, in $cm^3$, of $1.50 \text{ mol dm}^{-3}$ nitric acid required to react completely with $5.00 \text{ g}$ of solid bismuth(III) oxide.

(vi) Predict, with a reason, whether bismuth(III) oxide is expected to be primarily acidic, basic or amphoteric.

(vii) Discuss how the relative reactivity of zinc and bismuth could be established using the metals and aqueous solutions of their nitrates.

(viii) Discuss the products formed at the electrodes during the electrolysis of aqueous bismuth(III) nitrate. Use the standard electrode potential $E^\ominus(Bi^{3+}/Bi) = +0.32 \text{ V}$ and section 24 of the data booklet.

Bismuth compounds are sometimes used in fireworks to produce special effects.

(c) (i) State the feature of the atomic emission spectrum of an element that corresponds to its first ionization energy.

(ii) Calculate the wavelength, in nm, that corresponds to the first ionization energy of bismuth. Use sections 1, 2 and 8 of the data booklet.

(iii) Explain why the first ionization energy of bismuth is lower than that of polonium (Po), in terms of nuclear charge and electron shielding.

A sample of chlorine consists of two isotopes, $^{35}Cl$ and $^{37}Cl$.

(a) Contrast the sub-atomic structure of these two isotopes.

(b) (i) The sample of chlorine is analysed in a mass spectrometer, producing a spectrum for the $Cl_2^+$ ion. The spectrum shows three peaks at m/z values of 70, 72 and 74. Explain the origin and relative heights of these three peaks, given that the abundance of $^{35}Cl$ is approximately three times that of $^{37}Cl$.

(ii) A more precise measurement finds the composition by mass to be: $^{35}Cl$: 75.76%, $^{37}Cl$: 24.24%. Calculate the relative atomic mass of chlorine from this sample, giving your answer to two decimal places. (Use isotopic masses of 35.0 and 37.0 for this calculation).

Magnesium chloride, $MgCl_2$, and manganese(II) chloride, $MnCl_2$, are two ionic compounds.

(c) (i) Deduce the type of bonding in magnesium chloride, $MgCl_2$, using electronegativity values from section 9 of the data booklet.

(ii) Determine the lattice enthalpy of magnesium chloride, assuming the bonding is purely ionic. Use sections 9, 10 and 12 of the data booklet and the following data:

Enthalpy of formation of magnesium chloride = $-641 \text{ kJ mol}^{-1}$

(iii) Explain, with reference to electron configurations, why the ionic radii of $Mg^{2+}$, $Mn^{2+}$ and $Cl^-$ are different. Use section 10 of the data booklet.

(iv) Predict, with a reason, which has the stronger ionic bonding, manganese(II) chloride, $MnCl_2$, or magnesium chloride.

Magnesium chloride is white, but manganese(II) chloride is pale pink.

(d) (i) State the condensed electron configuration of a manganese atom.

(ii) State the reason, in terms of electron configuration, why manganese(II) chloride is coloured.

(iii) Manganese(II) chloride absorbs light with a wavelength of approximately 530 nm. Describe why this is consistent with the observed colour of the compound. Use sections 2 and 15 of the data booklet.

A copper key is to be electroplated with manganese using an aqueous solution of manganese(II) chloride as the electrolyte.

(e) (i) Deduce the half-equations for the reactions occurring at the anode (made of pure manganese) and the cathode (the copper key).

(ii) Deduce a balanced chemical equation for the reaction of fluorine gas with the aqueous chloride ions in the electrolyte.

Strontium is an alkaline earth metal in group 2 of the periodic table, used to produce the red colour in fireworks.

(a) In a sample of strontium, 10.0% of the atoms have a mass number of 86 and the remainder have a mass number of 88.

(i) Deduce the nuclear symbol of the isotope of strontium with mass number 86. Use section 6 of the data booklet.

(ii) Calculate, to two decimal places, the relative atomic mass of this sample of strontium.

(iii) Explain why the first ionization energy of strontium is greater than that of rubidium.

(b) Strontium nitrate has the formula $Sr(NO_3)_2$.

(i) The compound contains both ionic and covalent bonds. State which particles are joined by covalent bonds and which are joined by ionic bonds.

(ii) Contrast covalent and ionic bonds in terms of how the valence electrons are involved.

(iii) Write a balanced chemical equation for the formation of strontium nitrate solution from the reaction of solid strontium hydroxide with nitric acid.

(iv) Calculate the volume, in $cm^3$, of $1.50 \text{ mol dm}^{-3}$ nitric acid required to react completely with $5.00 \text{ g}$ of solid strontium hydroxide.

(v) Predict, with a reason, whether strontium oxide is acidic, basic or amphoteric.

(vi) Describe an experiment to establish the relative reactivity of strontium and zinc using the metals and aqueous solutions of their nitrates.

Brass is an alloy of copper and zinc.

(a) Describe the bonding in brass.

(b) Suggest why brass conducts electricity but zinc sulfide, an ionic compound, does not conduct electricity in the solid state.