IB Chemistry HL 3.1 The Periodic Table Questions

Practise periodic trends, group reactions, oxide and redox chemistry, then explore transition-metal ions, variable oxidation states, ligands and colours.

Exam points

Infer group, period and s/p/d/f block from electron configurations; classify elements from periodic position.
Compare periodic trends in atomic/ionic radius, ionization energy, electron affinity and electronegativity.
Explain periodic-trend directions and exceptions using nuclear charge, shielding, sublevels and electron pairing.
Explain Group 1 reactivity with water down the group using electron loss, equations and observations.
Compare Group 17 reactivity and predict halide displacements with ionic equations and colour evidence.
Classify Period 3 oxides as basic, amphoteric or acidic using pH and acid-base reactions.
Write balanced equations for Group 1/2 and carbon or sulfur oxides reacting with water.
Calculate oxidation states in compounds and ions, including average values in mixed-valence Fe3O4.
Use oxidation-state changes to identify redox, formulas or systematic names with Roman numerals.
Explain variable transition-metal oxidation states from successive ionization energies and 4s/3d configurations.
Identify transition elements from incomplete d-subshells and relate them to magnetic or catalytic behaviour.
Recognise ligands and complex ions, and describe their characteristic transition-element chemistry.
Explain complex colours through d-orbital splitting and use absorbed wavelengths to infer observed colours.

Covered syllabus points

3.1.1—Organization 3.1.2—Electron configuration and position 3.1.3—Periodicity 3.1.4—Group trends 3.1.5—Metal/non-metal continuum 3.1.6—Oxidation states 3.1.7 (HL)—IE discontinuities 3.1.8 (HL)—Transition element properties 3.1.9 (HL)—Variable oxidation states 3.1.10 (HL)—Transition element colors

[Maximum number: 5]

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.

(a)

Distinguish between the terms group and period.

[ 1 ]

(b)

State the other most common ion of cobalt.

[ 1 ]

$\mathrm{Co}^{2+}$ ;

Marking guidance:

Accept +2, 2+, cobalt(II), II.

(c)

Explain why the complex $\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right] \mathrm{Cl}_{3}$ is coloured.

[ 3 ]

[Maximum number: 6]

Iron rusts in the presence of oxygen and water. Rusting is a redox process involving several steps that produces hydrated iron(III) oxide, $\mathrm{Fe}_{2} \mathrm{O}_{3} \bullet \mathrm{nH}_{2} \mathrm{O}$ , as the final product. The half-equations involved for the first step of rusting are given below.

Half-equation 1: $\quad \mathrm{Fe}(\mathrm{s}) \rightarrow \mathrm{Fe}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-}$

Half-equation 2: $\quad \mathrm{O}_{2}(\mathrm{aq})+4 \mathrm{e}^{-}+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow 4 \mathrm{OH}^{-}(\mathrm{aq})$

(a)

Identify the oxidation number of each atom in the three species in half-equation 2.

Figure for Question (a) — IB Chemistry HL

[ 2 ]

$\mathrm{O}_{2}(aq)+4e^{-}+2\mathrm{H}_{2}\mathrm{O}(l) \rightarrow 4\mathrm{OH}^{-}(aq)$

Oxidation numbers:

Species/atom	Oxidation number
O in $\mathrm{O}_{2}$	0
H in $\mathrm{H}_{2}\mathrm{O}$	+I
O in $\mathrm{H}_{2}\mathrm{O}$	-II
O in $\mathrm{OH}^{-}$	-II
H in $\mathrm{OH}^{-}$	+I

Species/atom	Oxidation number
O in $\mathrm{O}_{2}$	0
H in $\mathrm{H}_{2}\mathrm{O}$	+I
O in $\mathrm{H}_{2}\mathrm{O}$	-II
O in $\mathrm{OH}^{-}$	-II
H in $\mathrm{OH}^{-}$	+I

(b)

State the relationship between the electron arrangement of an element and its group and period in the periodic table.

[ 2 ]

(c)

Transition metals and their compounds often catalyse reactions. The catalyzed decomposition of hydrogen peroxide by CuO is an example. State two other examples of catalyzed reactions giving the transition metal or its compound acting as catalyst.

[ 2 ]

$\quad \mathrm{V}_{2} \mathrm{O}_{5}$ catalyses oxidation of $\mathrm{SO}_{2}$ / $\mathrm{V}_{2} \mathrm{O}_{5}$ is a catalyst in the Contact Process; Fe catalyses the reaction between $\mathrm{N}_{2}$ and $\mathrm{H}_{2}$ / Fe is a catalyst in the Haber Process; $\mathrm{Ni} / \mathrm{Pd} / \mathrm{Pt}$ catalyses hydrogenation / manufacture of margarine / addition of hydrogen to C=C / conversion of alkenes to alkanes;
$\mathrm{Pd} / \mathrm{Pt}$ is a catalyst in catalytic converters / $\mathrm{Pd} / \mathrm{Pt}$ catalyzes reaction of $\mathrm{NO}_{2}$ and $\mathrm{CO}$ / $\mathrm{NO}_{2}$ and (unburnt) fuel/exhaust gases;

[Maximum number: 4]

Iron may be extracted from iron (II) sulfide, FeS.

(a)

Justify why sulfur is classified as a non-metal by giving two of its chemical properties.

[ 2 ]

(b)

Iron (II) sulfide, FeS, is ionically bonded.

[ 1 ]

(i)

Outline, in terms of their electronic structures, why the ionic radius of the sulfide ion is greater than that of the oxide ion.

[ 1 ]

(c)

The first step in the extraction of iron from iron (II) sulfide is to roast it in air to form iron (III) oxide and sulfur dioxide.

[ 1 ]

(i)

Deduce the change in the oxidation state of sulfur.

[ 1 ]

[Maximum number: 1]

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.

Distinguish between the terms group and period.

[Maximum number: 2]

Half-equation 1: $\quad \mathrm{Fe}(\mathrm{s}) \rightarrow \mathrm{Fe}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-}$

Half-equation 2: $\quad \mathrm{O}_{2}(\mathrm{aq})+4 \mathrm{e}^{-}+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow 4 \mathrm{OH}^{-}(\mathrm{aq})$

State the relationship between the electron arrangement of an element and its group and period in the periodic table.

[Maximum number: 1]

Iron may be extracted from iron (II) sulfide, FeS.

Iron (II) sulfide, FeS, is ionically bonded.

Outline, in terms of their electronic structures, why the ionic radius of the sulfide ion is greater than that of the oxide ion.

[Maximum number: 1]

Bleaches in which chlorine is the active ingredient are the most common, although some environmental groups have concerns about their use.

Describe the colour change that occurs when aqueous chlorine is added to aqueous sodium bromide.

[Maximum number: 3]

Magnesium is a group 2 metal which exists as a number of isotopes and forms many compounds.

(a)

Magnesium burns in air to form a white compound, magnesium oxide. Formulate an equation for the reaction of magnesium oxide with water.

[ 1 ]

$\mathrm{MgO}(s)+\mathrm{H}_{2}\mathrm{O}(l) \rightarrow \mathrm{Mg(OH)}_{2}(s)$

or:
$\mathrm{MgO}(s)+\mathrm{H}_{2}\mathrm{O}(l) \rightarrow \mathrm{Mg}^{2+}(aq)+2\mathrm{OH}^{-}(aq)$

(b)

Describe the trend in acid-base properties of the oxides of period 3, sodium to chlorine.

[ 2 ]

[Maximum number: 1]

Nitrous acid, $\mathrm{HNO}_{2}$ , is a weak acid which can be used to make acidic buffers.

A $1.00 \mathrm{~mol} \mathrm{dm}^{-3}$ solution of nitrous acid was prepared. This solution contains two conjugate acid-base pairs.

State the oxidation state of nitrogen in nitrous acid, $\mathrm{HNO}_{2}$ .

[Maximum number: 1]

Which statement explains one of the decreases in first ionization energy (I.E.) across period 3?

Figure for Question 10 — IB Chemistry HL

The nuclear charge of element Al is greater than element Mg .

The electron-electron repulsion is greater, for the electron with the opposite spin, in element S than in element P.

A new sub-level is being filled at element S .

The p orbital being filled in element Al is at a lower energy than the s orbital in element Mg .

[Maximum number: 1]

Beryllium is a low-density metal that is used in specialized lightweight alloys.

Iron (III) chloride also exists as a dimer in the vapour phase, but iron, unlike beryllium, is a transition element.

Outline, in terms of its electronic structure, what identifies a transition element.

[Maximum number: 3]

Beryllium is a low-density metal that is used in specialized lightweight alloys.

Iron (III) chloride also exists as a dimer in the vapour phase, but iron, unlike beryllium, is a transition element.

The first four ionization energies of beryllium and iron are shown.

Figure for Question 12 — IB Chemistry HL

One common property of transition elements is that they have variable oxidation states. Discuss, referring to the graph, why iron, but not beryllium, displays this characteristic.

IE values of Fe gradually increase

AND

IE values of Be show a sudden rise

first and second ionization energies close together therefore do not form a +1 oxidation state / singly charged ion

further IEs of Fe are close to second IE, so the oxidation state/number of electrons Fe loses can vary «according to the oxidizing agents present»

Marking guidance:

Accept Be always loses 2 electrons /
forms $\mathrm{Be}^{2+}$ / only has +2 oxidation state
for M2 .

[Maximum number: 4]

Titanium and vanadium are consecutive elements in the first transition metal series.

Outline why transition metals form coloured compounds.

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Covered syllabus points

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Question 2

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Question 3

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