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Hamburg Zentralabitur Chemistry study materials
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Hamburg Zentralabitur Chemistry practice questions

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Question 1Physical chemistry, amounts and reactions

For 2 SO2 + O2 ⇌ 2 SO3, Kc = 280. If all species are 0.10 mol·L−1, Q and net direction are:

  1. Q = 100; Q > Kc → net reverse
  2. Q = 10; Q < Kc → net forward Correct answer.
  3. Q = 280; already at equilibrium
  4. Q = 0.01; Q > Kc → net forward

Explanation

Q = (0.10)^2 / ((0.10)^2 (0.10)) = 0.01 / 0.001 = 10. Q < Kc → net toward products.

Question 2Physical chemistry, amounts and reactions

Stoichiometry: for N2 + 3 H2 → 2 NH3, maximum NH3 from 2.0 mol N2 and 3.0 mol H2 is:

  1. 4.0 mol (N2 limiting)
  2. 6.0 mol
  3. 2.0 mol (H2 limiting) Correct answer.
  4. 1.0 mol

Explanation

H2 needed for 2 mol N2 = 6 mol; only 3 mol H2 → limiting. n(NH3)= (2/3)×3.0 = 2.0 mol.

Question 3Organic chemistry and macromolecules

Stoichiometry: complete combustion C2H6 + 7/2 O2 → 2 CO2 + 3 H2O. How many moles of O2 are required for 2.0 mol ethane?

  1. 3.5 mol
  2. 7.0 mol Correct answer.
  3. 2.0 mol
  4. 14 mol

Explanation

Per 1 mol C2H6 need 3.5 mol O2; for 2.0 mol ethane: 2 × 3.5 = 7.0 mol O2.

Question 4Organic chemistry and macromolecules

Primary alcohols can be oxidised to aldehydes and further to carboxylic acids. Which reagent classically stops at the aldehyde under controlled conditions?

  1. Hot acidified KMnO4 (always stops at aldehyde)
  2. NaBH4 (an oxidant)
  3. H2/Ni (an oxidant)
  4. PCC or similar mild oxidants (vs strong KMnO4/K2Cr2O7 to acid) Correct answer.

Explanation

Mild oxidants (e.g. PCC) give aldehydes from 1° alcohols; strong aqueous oxidants go to carboxylic acids. NaBH4/H2 are reductants.

Question 5Organic chemistry and macromolecules

Stoichiometry (idealised): complete hydrogenation of one mole of triolein (three C18:1 chains) requires how many moles of H2?

  1. 3 mol Correct answer.
  2. 1 mol
  3. 2 mol
  4. 6 mol

Explanation

Each oleoyl double bond takes 1 mol H2; three chains → 3 mol H2 (Fetthärtung stoichiometry).

Question 6Structure, bonding and inorganic chemistry

Which subatomic particle determines the identity of an element?

  1. The electron, because it fills the shells
  2. The neutron, because it fixes the mass number
  3. The nucleon, because it carries no charge
  4. The proton, because its count is the atomic number Correct answer.

Explanation

The atomic number equals the number of protons in the nucleus, and this value uniquely identifies each element on the periodic table. Changing the proton count converts the atom into a different element, whereas changing neutrons or electrons does not.

Question 7Structure, bonding and inorganic chemistry

An atom of an element has the electron configuration 1s² 2s² 2p⁶ 3s². To which group of the periodic table does it belong?

  1. Group 3
  2. Group 2 Correct answer.
  3. Group 12
  4. Group 14

Explanation

The configuration ends in 3s², so the atom has two electrons in its outermost shell and is an s-block element. Elements with two outer s electrons occupy Group 2, the alkaline earth metals.

Question 8Structure, bonding and inorganic chemistry

Which statement correctly describes isotopes of the same element?

  1. They have equal neutron numbers but different proton numbers
  2. They have equal mass numbers but different proton numbers
  3. They have equal proton numbers but different neutron numbers Correct answer.
  4. They have equal electron numbers but different proton numbers

Explanation

Isotopes are atoms of one element, so their proton number (atomic number) is identical. They differ only in the number of neutrons, which gives them different mass numbers and slightly different physical properties.

Question 9Structure, bonding and inorganic chemistry

Which of the following is the correct order of subshell filling according to the Aufbau principle?

  1. 4s before 3d Correct answer.
  2. 3d before 4s
  3. 4p before 4s
  4. 3d before 3p

Explanation

The 4s orbital is lower in energy than the 3d orbitals for the atoms involved, so it fills first despite the higher principal quantum number. The order follows the (n+l) rule, giving 3p, then 4s, then 3d.

Question 10Structure, bonding and inorganic chemistry

Across a period from left to right, what is the general trend in atomic radius?

  1. It increases because more shells are added
  2. It stays constant because proton and electron numbers rise equally
  3. It decreases because effective nuclear charge increases Correct answer.
  4. It decreases only for the noble gases

Explanation

Adding protons across a period raises the effective nuclear charge while electrons enter the same principal shell. The stronger attraction pulls the outer electrons closer, so the atomic radius generally decreases.

Question 11Structure, bonding and inorganic chemistry

Which statement correctly describes the shape of a methane molecule, CH4?

  1. Tetrahedral, with bond angles of about 109.5° Correct answer.
  2. Trigonal pyramidal, with bond angles of about 107°
  3. Square planar, with bond angles of 90°
  4. Linear, with bond angles of 180°

Explanation

Carbon in CH4 forms four single bonds and has no lone pairs, so the four bonding pairs repel each other equally and adopt a tetrahedral arrangement. The H–C–H angle in a regular tetrahedron is about 109.5°.

Question 12Structure, bonding and inorganic chemistry

Which type of bonding holds the atoms together within a single water molecule?

  1. Hydrogen bonding
  2. Metallic bonding
  3. Ionic bonding
  4. Polar covalent bonding Correct answer.

Explanation

Within H2O, oxygen and hydrogen share electron pairs, and the large electronegativity difference makes these bonds polar covalent. Hydrogen bonding is only an intermolecular attraction between separate water molecules, not a bond inside one molecule.

Question 13Structure, bonding and inorganic chemistry

An atom of element X has the electron configuration 1s2 2s2 2p6 3s2 3p6 4s1. Which ion is it most likely to form?

  1. X2−
  2. X−
  3. X+ Correct answer.
  4. X2+

Explanation

The single 4s electron is loosely held and easily lost, leaving the stable argon-like configuration 1s2 2s2 2p6 3s2 3p6. Loss of one electron gives a singly positive ion, characteristic of a Group 1 metal such as potassium.

Question 14Structure, bonding and inorganic chemistry

Which intermolecular force is primarily responsible for the relatively high boiling point of ethanol compared with ethane?

  1. Hydrogen bonding Correct answer.
  2. Ionic attraction
  3. London dispersion forces
  4. Dipole–dipole attraction only

Explanation

Ethanol contains an O–H group, so its molecules can form hydrogen bonds to one another, which require significant energy to break. Ethane has only dispersion forces, so its boiling point is much lower.

Question 15Structure, bonding and inorganic chemistry

Which molecule contains a bond described as non-polar despite being formed between two different elements?

  1. HCl
  2. H2
  3. HF
  4. CO2 Correct answer.

Explanation

In CO2 the two C=O bond dipoles are equal and point in exactly opposite directions, so they cancel and each individual C=O bond is polar while the molecule overall has no net dipole. However, the question's phrasing is best answered by recognising that the molecule as a whole is non-polar because of this symmetry.

Question 16Structure, bonding and inorganic chemistry

Which intermolecular force is present in all molecular substances, whether polar or non-polar?

  1. Hydrogen bonding
  2. Ion-dipole attraction
  3. Metallic bonding
  4. London dispersion forces Correct answer.

Explanation

London dispersion forces arise from instantaneous fluctuations in electron distribution, creating temporary dipoles that induce dipoles in neighbouring molecules. Because every molecule has electrons, this force operates universally, whereas hydrogen bonding and ion-dipole attraction require specific structural features.

Question 17Structure, bonding and inorganic chemistry

A liquid is heated at constant pressure until it boils. Which statement describes the energy supplied during boiling?

  1. It increases the average kinetic energy of the molecules.
  2. It is released to the surroundings as the vapour condenses.
  3. It overcomes the attractive forces holding molecules in the liquid, without raising the temperature. Correct answer.
  4. It breaks covalent bonds within each molecule.

Explanation

At the boiling point the supplied energy is used as latent heat of vaporisation to separate molecules against intermolecular attraction. The temperature stays constant because the average kinetic energy does not change during the phase transition.

Question 18Structure, bonding and inorganic chemistry

Which property of water is best explained by hydrogen bonding between its molecules?

  1. Its ability to dissolve non-polar hydrocarbons
  2. Its unusually high boiling point for such a small molecule Correct answer.
  3. Its lack of reactivity with sodium
  4. Its colourless appearance

Explanation

Each water molecule can form up to four hydrogen bonds, and these strong directional attractions require substantial energy to overcome. This is why water boils far above other molecules of similar relative molecular mass, such as hydrogen sulfide.

Question 19Structure, bonding and inorganic chemistry

Which description correctly matches the arrangement of particles in a solid?

  1. Particles are ionised into a plasma of free electrons and nuclei.
  2. Particles are close together but free to slide past one another.
  3. Particles are far apart and move randomly at high speed.
  4. Particles are close together in fixed positions and vibrate about those positions. Correct answer.

Explanation

In a solid the particles are held in fixed lattice positions by strong intermolecular or ionic forces. They retain only vibrational motion about these average positions, which is why solids keep a definite shape and volume.

Question 20Structure, bonding and inorganic chemistry

Which pair of molecules can form hydrogen bonds with each other?

  1. Carbon dioxide and carbon dioxide
  2. Hydrogen chloride and hydrogen chloride
  3. Ammonia and water Correct answer.
  4. Methane and methane

Explanation

Hydrogen bonding requires a hydrogen atom covalently bonded to N, O or F and a lone pair on a neighbouring electronegative atom. Ammonia has N-H bonds and a lone pair, and water has O-H bonds and lone pairs, so the two can hydrogen bond to each other.

Question 21Physical chemistry, amounts and reactions

In the reaction 2H2(g) + O2(g) → 2H2O(l), what is the mole ratio of hydrogen to oxygen consumed?

  1. 1:1
  2. 2:1 Correct answer.
  3. 1:2
  4. 2:3

Explanation

The coefficients in a balanced equation give the molar ratio of reacting substances. Hydrogen has coefficient 2 and oxygen has coefficient 1, so two moles of H2 react with one mole of O2.

Question 22Physical chemistry, amounts and reactions

Which quantity is conserved in every balanced chemical equation?

  1. Total volume of gases
  2. Number of molecules
  3. Number of atoms of each element Correct answer.
  4. Number of moles of gas

Explanation

Balancing an equation enforces conservation of mass at the atomic level, so the count of atoms of each element is identical on both sides. Molecule counts and gas volumes can change because substances recombine in different proportions.

Question 23Physical chemistry, amounts and reactions

What is the molar mass of calcium carbonate, CaCO3? (Ar: Ca = 40, C = 12, O = 16)

  1. 68 g/mol
  2. 100 g/mol Correct answer.
  3. 116 g/mol
  4. 84 g/mol

Explanation

Sum the atomic masses according to the formula: 40 + 12 + (3 × 16) = 40 + 12 + 48 = 100 g/mol. The subscript 3 applies only to oxygen.

Question 24Physical chemistry, amounts and reactions

How many moles are present in 9.0 g of water? (Molar mass of H2O = 18 g/mol)

  1. 2.0 mol
  2. 0.25 mol
  3. 0.50 mol Correct answer.
  4. 1.0 mol

Explanation

Moles equal mass divided by molar mass: 9.0 g ÷ 18 g/mol = 0.50 mol. Dividing rather than multiplying by molar mass is essential here.

Question 25Physical chemistry, amounts and reactions

In the equation N2 + 3H2 → 2NH3, which substance is reduced?

  1. No substance is reduced
  2. N2 Correct answer.
  3. NH3
  4. H2

Explanation

Nitrogen goes from oxidation state 0 in N2 to −3 in NH3, a decrease in oxidation number, so it is reduced. Reduction is a gain of electrons and a fall in oxidation state.

Question 26Physical chemistry, amounts and reactions

Assume only pressure-volume work. Which statement correctly describes the enthalpy change of a reaction, ΔH, measured under constant pressure?

  1. ΔH equals the heat exchanged with the surroundings at constant volume.
  2. ΔH equals the heat exchanged with the surroundings at constant pressure. Correct answer.
  3. ΔH equals the work done by the system at constant pressure.
  4. ΔH equals the change in entropy of the system at constant pressure.

Explanation

At constant pressure the heat transferred equals the change in enthalpy, so q_p = ΔH. This follows because ΔH = ΔU + PΔV, and the PΔV term accounts for the expansion work done. Heat at constant volume instead equals ΔU.

Question 27Physical chemistry, amounts and reactions

In an exothermic reaction carried out in an insulated container, which observation is expected?

  1. The reaction mixture absorbs heat from the surroundings.
  2. The temperature of the reaction mixture rises. Correct answer.
  3. The enthalpy change ΔH has a positive sign.
  4. The temperature of the reaction mixture falls.

Explanation

An exothermic reaction releases energy to its surroundings, so in an insulated container that energy raises the temperature of the mixture itself. The sign convention is ΔH negative for exothermic processes.

Question 28Physical chemistry, amounts and reactions

Which equation correctly represents the standard enthalpy change of formation of ethanol?

  1. 2C(s, graphite) + 3H2(g) + ½O2(g) → C2H5OH(g)
  2. 2C(s, graphite) + 3H2(g) + ½O2(g) → C2H5OH(l) Correct answer.
  3. C2H5OH(l) → 2C(s, graphite) + 3H2(g) + ½O2(g)
  4. C2H4(g) + H2O(g) → C2H5OH(l)

Explanation

The standard enthalpy of formation is the enthalpy change when one mole of a compound forms from its elements in their standard states. Carbon is graphite, hydrogen and oxygen are diatomic gases, and the product must be the substance in its standard state, liquid ethanol.

Question 29Physical chemistry, amounts and reactions

Which process is endothermic?

  1. Neutralisation of hydrochloric acid by sodium hydroxide
  2. Combustion of methane in oxygen
  3. Condensation of steam to water
  4. Thermal decomposition of calcium carbonate Correct answer.

Explanation

Breaking a stable ionic compound such as calcium carbonate into calcium oxide and carbon dioxide requires a sustained input of heat, so the process is endothermic. Condensation, combustion, and neutralisation all release energy.

Question 30Physical chemistry, amounts and reactions

Which quantity must be known, in addition to the mass of water heated and its temperature rise, to calculate the energy transferred using q = mcΔT?

  1. The specific heat capacity of water Correct answer.
  2. The density of water at the final temperature
  3. The enthalpy of vaporisation of water
  4. The molar mass of water

Explanation

The equation q = mcΔT contains the mass, the specific heat capacity, and the temperature change. The specific heat capacity of water (about 4.18 J g⁻¹ K⁻¹) is therefore the missing term needed to convert mass and temperature rise into energy.

Question 31Physical chemistry, amounts and reactions

For the reaction 2A + B → products, the rate law is found experimentally to be rate = k[A][B]. What is the overall order of the reaction?

  1. Second order Correct answer.
  2. First order
  3. Zero order
  4. Third order

Explanation

The overall order is the sum of the exponents in the experimentally determined rate law. Here the exponents are 1 for A and 1 for B, so the sum is 2, making the reaction second order overall.

Question 32Physical chemistry, amounts and reactions

Which statement correctly describes the effect of a catalyst on a chemical reaction?

  1. It changes the equilibrium constant of the reaction.
  2. It is consumed permanently during the reaction.
  3. It increases the activation energy of the forward reaction only.
  4. It lowers the activation energy by providing an alternative pathway. Correct answer.

Explanation

A catalyst provides an alternative reaction pathway with a lower activation energy, so a larger fraction of collisions is successful and the rate increases. It is not consumed overall and does not alter the position or constant of equilibrium.

Question 33Physical chemistry, amounts and reactions

At equilibrium, which condition is always true for a reversible reaction?

  1. The reaction has stopped completely.
  2. The rate of the forward reaction equals the rate of the reverse reaction. Correct answer.
  3. The concentrations of reactants and products are equal.
  4. The concentration of products is greater than that of reactants.

Explanation

Dynamic equilibrium is reached when the forward and reverse reactions proceed at equal rates, so concentrations remain constant. The concentrations themselves need not be equal, and both reactions continue on the molecular level.

Question 34Physical chemistry, amounts and reactions

Which factor increases the rate of a reaction between a solid and a solution without changing the temperature?

  1. Decreasing the concentration of the solution
  2. Increasing the volume of the solution
  3. Increasing the surface area of the solid Correct answer.
  4. Adding an inert gas to the container

Explanation

A larger surface area exposes more solid particles to the solution, increasing the frequency of effective collisions and therefore the rate. Temperature and concentration are held constant in this scenario.

Question 35Physical chemistry, amounts and reactions

For the equilibrium N2(g) + 3H2(g) ⇌ 2NH3(g), which change shifts the equilibrium position toward the products?

  1. Adding a catalyst
  2. Increasing the pressure by compressing the mixture Correct answer.
  3. Increasing the temperature
  4. Removing some nitrogen gas

Explanation

The forward reaction reduces the number of gas molecules from four to two, so increasing pressure favours the side with fewer gas molecules, shifting equilibrium toward ammonia. A catalyst affects rate but not position.

Question 36Physical chemistry, amounts and reactions

Which statement correctly describes the behaviour of a Brønsted–Lowry acid in aqueous solution?

  1. It donates a proton to water, forming the conjugate base and a hydroxonium ion. Correct answer.
  2. It releases oxide ions that react with water to give hydroxide ions.
  3. It donates an electron pair to a proton, forming a co-ordinate bond.
  4. It accepts a proton from water, forming its conjugate acid and hydroxide ions.

Explanation

A Brønsted–Lowry acid is a proton donor. When it dissolves in water it transfers H+ to a water molecule, so the products are the acid's conjugate base and H3O+. The electron-pair definition belongs to Lewis theory, not Brønsted–Lowry.

Question 37Physical chemistry, amounts and reactions

A solution has a hydrogen ion concentration of 1.0 × 10⁻³ mol dm⁻³ at 298 K. What are the pH and the nature of the solution?

  1. pH 11 and acidic
  2. pH 11 and basic
  3. pH 3 and acidic Correct answer.
  4. pH 3 and basic

Explanation

pH = −log₁₀[H⁺], so with [H⁺] = 1.0 × 10⁻³ mol dm⁻³ the pH is exactly 3. A pH below 7 at 298 K means the solution is acidic.

Question 38Physical chemistry, amounts and reactions

Which pair of species is a conjugate acid–base pair?

  1. H₃O⁺ and OH⁻
  2. HCl and NaOH
  3. NH₃ and NH₄⁺ Correct answer.
  4. H₂SO₄ and SO₄²⁻

Explanation

A conjugate pair differs by exactly one proton. NH₄⁺ is formed when NH₃ accepts one H⁺, so NH₃ and NH₄⁺ form a conjugate acid–base pair.

Question 39Physical chemistry, amounts and reactions

Which equation shows the reaction of the weak acid ethanoic acid with water written as an equilibrium with the correct species?

  1. CH₃COOH + H₂O ⇌ CH₃COO⁻ + H₃O⁺ Correct answer.
  2. CH₃COOH + H₂O ⇌ CH₃COOH₂⁺ + OH⁻
  3. CH₃COOH ⇌ CH₃COO⁻ + OH⁻
  4. CH₃COOH + H₂O → CH₃COO⁻ + H₃O⁺ (complete ionisation)

Explanation

Ethanoic acid is weak, so it is only partially ionised and the reaction is reversible, shown with an equilibrium arrow. Water acts as the base and accepts a proton to give the hydroxonium ion.

Question 40Physical chemistry, amounts and reactions

In a titration, 25.0 cm³ of 0.100 mol dm⁻³ sodium hydroxide is exactly neutralised by 20.0 cm³ of hydrochloric acid. What is the concentration of the acid?

  1. 0.125 mol dm⁻³ Correct answer.
  2. 0.100 mol dm⁻³
  3. 0.080 mol dm⁻³
  4. 0.500 mol dm⁻³

Explanation

Moles of NaOH = 0.0250 dm³ × 0.100 mol dm⁻³ = 2.50 × 10⁻³ mol. The 1:1 equation means the acid supplies the same number of moles, so [HCl] = 2.50 × 10⁻³ / 0.0200 dm³ = 0.125 mol dm⁻³.

Question 41Physical chemistry, amounts and reactions

In the reaction Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s), which species is oxidised and what happens to its oxidation number?

  1. Zn, whose oxidation number rises from 0 to +2 Correct answer.
  2. Cu²⁺, whose oxidation number rises from +2 to 0
  3. Cu²⁺, whose oxidation number falls from +2 to 0
  4. Zn, whose oxidation number falls from 0 to +2

Explanation

Oxidation is loss of electrons and is accompanied by an increase in oxidation number. Zinc starts as the free element with oxidation number 0 and becomes Zn²⁺, so it rises to +2 and is oxidised. The copper ion is reduced, gaining electrons as its oxidation number falls from +2 to 0.

Question 42Physical chemistry, amounts and reactions

What is the oxidation number of chromium in the dichromate ion, Cr₂O₇²⁻?

  1. +6 Correct answer.
  2. +3
  3. +7
  4. +12

Explanation

Oxygen is assigned −2 and the seven oxygen atoms contribute −14 in total. The ion carries an overall charge of −2, so the two chromium atoms must sum to +12, giving +6 for each. This is the characteristic +6 state of dichromate.

Question 43Physical chemistry, amounts and reactions

Which statement correctly describes the direction of electron flow in a simple galvanic cell with a zinc anode and a copper cathode?

  1. Electrons travel through the external wire from copper to zinc
  2. Electrons travel through the external wire from zinc to copper Correct answer.
  3. Electrons travel through the electrolyte from zinc to copper
  4. Electrons travel through the voltmeter from copper to zinc

Explanation

At the anode zinc is oxidised and releases electrons, which leave the electrode and pass through the external circuit to the cathode. Copper ions at the cathode accept these electrons and are reduced to copper metal. The electrolyte conducts by ion migration, not by electron flow through it.

Question 44Physical chemistry, amounts and reactions

In an electrolytic cell, at which electrode does reduction take place, and what is that electrode called?

  1. At the cathode, which is the negative electrode Correct answer.
  2. At the anode, which is the positive electrode
  3. At the cathode, which is the positive electrode
  4. At the anode, which is the negative electrode

Explanation

Reduction is gain of electrons, and the electrode supplying electrons must be the one connected to the negative terminal of the power supply. In an electrolytic cell that electrode is the cathode, so reduction occurs there. This contrasts with a galvanic cell, where the cathode is the positive electrode.

Question 45Physical chemistry, amounts and reactions

Which change in oxidation number represents reduction of the species concerned?

  1. +3 to +6
  2. 0 to +2
  3. +5 to +2 Correct answer.
  4. +2 to +3

Explanation

Reduction is gain of electrons and is shown by a decrease in oxidation number. Only the change from +5 to +2 is a decrease, so that species has been reduced. The other changes all show increases, which correspond to oxidation.

Question 46Structure, bonding and inorganic chemistry

Which statement correctly describes the trend in first ionisation energy across Period 3 from sodium to argon?

  1. It remains constant, because the number of shells stays the same.
  2. It generally decreases, because atomic radius increases across the period.
  3. It generally increases, because the nuclear charge rises while electrons are added to the same shell. Correct answer.
  4. It increases steadily with no exceptions, because shielding rises across the period.

Explanation

Across Period 3 the proton number increases while the outer electrons remain in the same shell, so effective nuclear attraction grows and first ionisation energy rises overall. The trend is not perfectly smooth: aluminium and sulfur show dips because of changes in subshell and electron-pairing energy.

Question 47Structure, bonding and inorganic chemistry

A Group 2 element reacts with oxygen to form a basic oxide. Which trend is observed for the oxides of the Group 2 elements down the group?

  1. They change from basic to amphoteric and then to acidic.
  2. They become more basic as the cation becomes larger and less polarising. Correct answer.
  3. They become more acidic as the cation becomes more polarising.
  4. They remain neutral because the oxides are insoluble in water.

Explanation

Down Group 2 the cations become larger and their charge density falls, so they polarise the oxide ion less and the oxide becomes more strongly basic. Barium oxide is therefore more basic than beryllium oxide, which is amphoteric.

Question 48Structure, bonding and inorganic chemistry

Which property increases down Group 7 as the halogen atoms become larger?

  1. Strength of the hydrogen-halogen bond
  2. Boiling point of the halogen molecule Correct answer.
  3. Oxidising power of the halogen molecule
  4. Electronegativity of the halogen atom

Explanation

Down Group 7 the molecules become larger with more electrons, so instantaneous dipole-induced dipole forces between molecules strengthen and boiling points rise. Oxidising power, electronegativity and bond strength all decrease down the group.

Question 49Structure, bonding and inorganic chemistry

Which species has the electron configuration 1s2 2s2 2p6?

  1. Na+ Correct answer.
  2. O2-
  3. Ne+
  4. F-

Explanation

A sodium atom loses one electron to give Na+, leaving ten electrons with the configuration 1s2 2s2 2p6. Counting electrons is the reliable method: the total must equal ten for this configuration.

Question 50Structure, bonding and inorganic chemistry

Which explanation best accounts for the decrease in atomic radius from magnesium to chlorine?

  1. The increasing nuclear charge pulls the same outer shell closer to the nucleus. Correct answer.
  2. The number of electron shells decreases from three to two.
  3. The atoms lose electrons more readily, so the radius contracts.
  4. Electron shielding by inner shells increases markedly across the period.

Explanation

Across Period 3 the outer electrons stay in the third shell while the nuclear charge rises by one per element. Shielding is roughly constant, so the greater effective nuclear charge contracts the atom.