Question
Lithium and boron are elements in period 2 of the periodic table. Lithium occurs in group 1 (the alkali metals) and boron occurs in group 3. Isotopes exist for both elements.
Every element has its own unique line emission spectrum.
(i) Define the terms atomic number, mass number and isotopes of an element.
Atomic number:
Mass number:
Isotopes of an element:
(ii) Distinguish between the terms group and period.
(iii) Deduce the electron arrangements of the lithium ion, \({\text{L}}{{\text{i}}^ + }\), and the boron atom, B.
\({\text{L}}{{\text{i}}^ + }\):
B:
(iv) Naturally occurring boron exists as two isotopes with mass numbers of 10 and 11. Calculate the percentage abundance of the lighter isotope, using this information and the relative atomic mass of boron in Table 5 of the Data Booklet.
v) Lithium exists as two isotopes with mass numbers of 6 and 7. Deduce the number of protons, electrons and neutrons for each isotope.
(i) Distinguish between a continuous spectrum and a line spectrum.
(ii) Draw a diagram to show the electron transitions between energy levels in a hydrogen atom that are responsible for the two series of lines in the ultraviolet and visible regions of the spectrum. Label your diagram to show three transitions for each series.
(i) Explain why metals are good conductors of electricity and why they are malleable.
(ii) Iron is described as a transition metal. Identify the two most common ions of iron.
iii) Deduce the chemical formulas of lithium oxide and iron(II) oxide.
Lithium oxide:
Iron(II) oxide:
Answer/Explanation
Markscheme
(i) Atomic number:
number of protons (in nucleus/atom);
Mass number:
(sum of) number of protons and neutrons (in nucleus/atom);
Isotopes of an element:
atoms of same element / atoms with same number of protons/atomic number/Z but different number of neutrons/mass number/A;
Penalize once only use of the term element in the three definitions, for example, number of protons in an element or number of protons and neutrons in an element or element with the same atomic number but different mass number.
(ii) Group: (elements in vertical) columns in periodic table and Period: (elements in horizontal) rows in periodic table;
Allow elements in same group have similar chemical properties and within a period, atoms have same number of shells/energy levels (but number of electrons in valence/outer shell increases).
Allow groups distributed vertically and periods distributed horizontally / OWTTE.
Allow group number gives number of valence/outer shell electrons (for maingroup elements) and period gives same number of shells/energy levels.
(iii) Li+: 2/1s2;
B: 2,3/1s22s22p1;
(iv) correct mathematical expression set-up \({\text{(e.g. }}\left( {\frac{x}{{100}}} \right)(10) + \left[ {\frac{{(100 – x)}}{{(100)}}} \right](11) = 10.81)\);
19%;
Award [2] for correct final answer.
(v) 
Award [1 max] for correct number of neutrons for both isotopes if numbers of protons or electrons is not given.
Award [1 max] for correct number of protons and electrons for both isotopes if number of neutrons is not given or if numbers of neutrons are incorrect.
(i) Continuous spectrum: radiation spread over all wavelengths/frequencies/energies/colours / OWTTE;
Line spectrum: radiation (absorbed/emitted) at certain/specific wavelengths/frequencies/energies/colours / OWTTE;
Allow series of (separate/discrete) lines which converge/get closer together at high energy / OWTTE.
(ii) 
showing y-axis labelled as energy/E or labelling at least two energy levels
(\(n = 1\), \(n = 2\) etc. but not for \(n = 0\));
showing energy levels converging;
showing jumps to \(n = 1\) for ultraviolet series;
showing jumps to \(n = 2\) for visible series;
UV and visible must be labelled.
(i) metals have delocalized electrons / sea of electrons which are mobile/can move / OWTTE;
layers/positive ions/cations/atoms slide past/over each other / OWTTE;
Do not accept nuclei for M2.
(ii) Fe2+ and Fe3+ ;
(iii) Lithium oxide: Li2O and Iron(II) oxide: FeO;
Examiners report
Many candidates defined the atomic number, mass number and isotopes correctly although the weaker candidates incorrectly used the term element instead of atom and others defined mass number in terms of molar mass instead of sum of protons and neutrons in the nucleus. Distinguishing between a group and a period and deducing the electron arrangements of Li+ and boron was handled well by majority of candidates. Many candidates struggled to calculate the percentage abundance of the lighter isotope whereas in part (v), most candidates correctly deduced the number of protons, neutrons and electrons in the two isotopes of lithium.
Distinguishing between a continuous and line spectrum in part (b) proved difficult for many candidates. Similarly, drawing a diagram to show the electron transitions between energy levels in a hydrogen atom was challenging for many candidates. Common errors seen were: starting incorrectly at \(n = 0\), not showing convergence or mixed up between the ultraviolet and visible lines.
In Part (c), although the explanation of why metals are good conductors of electricity was answered well, some candidates did not refer to delocalized or sea of electrons. Explanation of why metals are malleable proved to be difficult for many candidates. Identifying the two most common ions of iron and deducing chemical formulas was correctly answered by majority of the candidates.
Question
Calcium nitrate contains both covalent and ionic bonds.
Nitrogen also forms oxides, which are atmospheric pollutants.
State the formula of both ions present and the nature of the force between these ions.
Ions:
Nature of force:
State which atoms are covalently bonded.
Outline the source of these oxides.
State one product formed from their reaction with water.
State one environmental problem caused by these atmospheric pollutants.
Answer/Explanation
Markscheme
\({\text{C}}{{\text{a}}^{2 + }}\) and \({\text{NO}}_3^ – \);
electrostatic (attraction);
Do not accept ionic.
nitrogen/N and oxygen/O;
Do not accept nitrate/NO3–.
Accept atoms in nitrate/NO3–.
produced by high temperature combustion;
Accept combustion/jet/car engines / car exhaust/emissions / lightning / action of bacteria/microorganisms.
Do not accept combustion/burning, cars, planes, jets, factories, power plants etc.
nitric acid/\({\text{HN}}{{\text{O}}_{\text{3}}}\) / nitrous acid/nitric(III) acid/\({\text{HN}}{{\text{O}}_{\text{2}}}\);
Accept “forms acidic solutions / acid rain”.
acid deposition/rain / respiratory problems / corrosion problems / decomposition of ozone layer / photochemical smog / acidification/pollution of lakes / damage to plants/ trees;
Accept “acid rain” in either part (ii) or part (iii) but not both.
Do not accept air pollution.
Examiners report
This question was surprisingly very poorly answered. In part (a), it was distressing to see a large number of candidates who could not write the correct charge or formula of nitrate ion. In addition, the terminology appears to have confused a number of candidates and for the nature of force, ionic bonding was often stated which was incorrect, as electrostatic attraction was required. In (a) (ii), again candidates failed to answer the question and nitrate was commonly given which was not accepted. The question specifically asked for the atoms involved.
This question was surprisingly very poorly answered. In part (a), it was distressing to see a large number of candidates who could not write the correct charge or formula of nitrate ion. In addition, the terminology appears to have confused a number of candidates and for the nature of force, ionic bonding was often stated which was incorrect, as electrostatic attraction was required. In (a) (ii), again candidates failed to answer the question and nitrate was commonly given which was not accepted. The question specifically asked for the atoms involved.
In part (b), the Aim 8 component of AS 3.3.2 was assessed and this was very poorly answered overall. Inevitably, owing to some overlap in assessment statements these concepts would be more familiar to those studying the Environmental Chemistry option, but undoubtedly studying other options assists in other areas, such as organic chemistry. In (b) (i), many candidates gave generic answers such as cars or factories which did not score. In (ii), many incorrect answers were given such as nitrogen oxides, hydrogen or ozone. In (iii), acid rain was frequently seen and many referred to depletion of the ozone layer. However it was extremely disappointing that many candidates gave the greenhouse effect or global warming or air pollution as the answer, which of course scored no marks.
In part (b), the Aim 8 component of AS 3.3.2 was assessed and this was very poorly answered overall. Inevitably, owing to some overlap in assessment statements these concepts would be more familiar to those studying the Environmental Chemistry option, but undoubtedly studying other options assists in other areas, such as organic chemistry. In (b) (i), many candidates gave generic answers such as cars or factories which did not score. In (ii), many incorrect answers were given such as nitrogen oxides, hydrogen or ozone. In (iii), acid rain was frequently seen and many referred to depletion of the ozone layer. However it was extremely disappointing that many candidates gave the greenhouse effect or global warming or air pollution as the answer, which of course scored no marks.
In part (b), the Aim 8 component of AS 3.3.2 was assessed and this was very poorly answered overall. Inevitably, owing to some overlap in assessment statements these concepts would be more familiar to those studying the Environmental Chemistry option, but undoubtedly studying other options assists in other areas, such as organic chemistry. In (b) (i), many candidates gave generic answers such as cars or factories which did not score. In (ii), many incorrect answers were given such as nitrogen oxides, hydrogen or ozone. In (iii), acid rain was frequently seen and many referred to depletion of the ozone layer. However it was extremely disappointing that many candidates gave the greenhouse effect or global warming or air pollution as the answer, which of course scored no marks.