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SPM Chemistry practice questions

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Question 1Matter and its importance / Jirim dan kepentingannya

Why can a gas be compressed easily while a solid cannot?

  1. The particles in a gas have no attractive forces at all between them.
  2. The particles in a gas are very far apart, leaving large empty spaces between them. Correct answer.
  3. The gas particles move randomly at high speed and keep hitting the walls of the container.
  4. The particles in a gas are much smaller than the particles in a solid.

Explanation

In a gas the particles are spaced very far apart, so most of the volume is empty space; when pressure is applied the particles can be pushed closer together. In a solid the particles are already packed closely in a fixed arrangement, so there is almost no free space left to squeeze. The large empty space, not the size of the particles, is therefore the reason a gas is compressible.

Question 2Matter and its importance / Jirim dan kepentingannya

Which of the following substances is composed of ions?

  1. Oxygen gas
  2. Ethanol
  3. Sodium chloride Correct answer.
  4. Carbon dioxide

Explanation

Sodium chloride is an ionic compound built from Na+ and Cl- ions held in a giant ionic lattice by strong electrostatic forces, so it is described as composed of ions. Oxygen, ethanol and carbon dioxide are covalent substances whose particles are molecules. The type of particle present is a key classification of matter.

Question 3Matter and its importance / Jirim dan kepentingannya

A solid changes directly into a gas without first becoming a liquid. What is this change of state called?

  1. Deposition
  2. Condensation
  3. Fusion
  4. Sublimation Correct answer.

Explanation

Sublimation is the direct change of a solid into a gas without passing through the liquid state, and it happens when the particles gain enough energy to escape from the solid lattice completely. Iodine and dry ice (solid carbon dioxide) sublime at room conditions. The reverse change, gas straight to solid, is deposition.

Question 4Matter and its importance / Jirim dan kepentingannya

A crystal of potassium manganate(VII) is dropped into water at 30 °C and into water at 70 °C. The purple colour spreads through the warmer water much faster. Which explanation is correct?

  1. The water particles at the higher temperature carry the purple colour to the bottom of the beaker.
  2. The two substances react chemically faster at the higher temperature.
  3. The particles gain kinetic energy and move faster, so diffusion happens more quickly. Correct answer.
  4. The particles of potassium manganate(VII) become smaller as the temperature rises.

Explanation

Diffusion is the spreading of particles from a region of higher concentration to a region of lower concentration due to their random motion. At a higher temperature the particles of both the crystal and the water have greater average kinetic energy and move faster, so they mix in a shorter time. Heating does not change particle size or cause a chemical reaction here.

Question 5Matter and its importance / Jirim dan kepentingannya

Crushed ice at 0 °C is heated gently and stirred until all of it has melted, and the temperature stays at 0 °C the whole time. What happens to the heat energy supplied?

  1. It is lost to the surroundings because the ice is much colder than the surrounding air in the laboratory.
  2. It is used to overcome the attractive forces between water molecules as the solid turns into a liquid. Correct answer.
  3. It is used to increase the average kinetic energy of the water molecules.
  4. It is stored as chemical energy in the water molecules that are formed.

Explanation

While a solid melts, the heat supplied is absorbed as the latent heat of fusion and is used to overcome the forces of attraction holding the particles in the solid lattice. The energy does not raise the average kinetic energy of the particles, so the temperature stays constant until all the solid has melted. A constant temperature therefore does not mean that no heat is being absorbed.

Question 6Matter and its importance / Jirim dan kepentingannya

Which statement correctly compares boiling with evaporation?

  1. Boiling occurs at any temperature, while evaporation occurs only at the boiling point of the liquid.
  2. Boiling occurs at a fixed temperature with bubbles forming throughout the liquid, while evaporation occurs at any temperature at the surface. Correct answer.
  3. Boiling happens only in pure liquids, while evaporation happens only in solutions and mixtures.
  4. Boiling takes place only at the surface of the liquid, while evaporation takes place throughout the whole liquid at all temperatures.

Explanation

Boiling happens at one fixed temperature, the boiling point, and vapour bubbles form throughout the liquid because the vapour pressure equals the atmospheric pressure. Evaporation happens at any temperature below the boiling point and only from the surface of the liquid. Both processes change liquid into vapour but differ in the conditions and the place where they occur.

Question 7Matter and its importance / Jirim dan kepentingannya

A mixture consists of two miscible liquids with boiling points of 78 °C and 100 °C. Which method is most suitable for separating them?

  1. Separating funnel
  2. Filtration
  3. Fractional distillation Correct answer.
  4. Sublimation

Explanation

Miscible liquids with different boiling points are separated by fractional distillation: the liquid with the lower boiling point vaporises first, is condensed and collected, and the second liquid is collected afterwards. The fractionating column allows repeated condensation and vaporisation so that a good separation is obtained. Filtration and separating funnels work with solids and immiscible liquids, not with miscible liquids.

Question 8Matter and its importance / Jirim dan kepentingannya

A pure solid is heated strongly. Its temperature rises to 80 °C and then stays constant for several minutes; it then rises again to 210 °C, where it stays constant until the substance has completely turned into a gas. Which deduction is correct?

  1. The substance boils at 80 °C and melts at a temperature of 210 °C.
  2. Between 80 °C and 210 °C the substance exists completely as a gas.
  3. At 80 °C the solid is melting and both solid and liquid are present. Correct answer.
  4. The substance must be an impure mixture because its heating curve shows two constant temperatures.

Explanation

Each flat section of the heating curve occurs while a change of state is taking place, since the heat supplied becomes latent heat instead of raising the temperature. The first plateau at 80 °C is the melting point, where solid and liquid coexist, and the second at 210 °C is the boiling point, where liquid and gas coexist. Between the two plateaus the substance is entirely liquid.

Question 9Matter and its importance / Jirim dan kepentingannya

A student heats two samples of naphthalene: sample P is pure, while sample Q contains a small amount of an impurity. Which observation is expected?

  1. Q melts at a higher temperature than P and over a narrower range of temperature.
  2. Q melts at a lower temperature than P and over a wider range of temperature. Correct answer.
  3. Q melts at the same temperature as P but takes a much longer time to melt completely.
  4. Q does not melt at all because the impurity raises the melting point of naphthalene.

Explanation

An impurity lowers the melting point of a substance and causes it to melt gradually over a range of temperatures rather than sharply at one value. The more impurity present, the lower the melting point and the wider the melting range. This is why a sharp melting point is used as a test for the purity of a solid.

Question 10Matter and its importance / Jirim dan kepentingannya

A sealed, flexible plastic bottle full of air is placed in a freezer, and after a while the bottle is slightly dented because its volume has decreased. Which explanation is correct?

  1. At the lower temperature the particles move more slowly, so the pressure inside the bottle decreases. Correct answer.
  2. The air particles combine with one another so that there are fewer particles inside the bottle.
  3. Some of the air particles escape through the walls of the plastic bottle and this makes it dent.
  4. The air particles shrink in size when they are cooled in the freezer.

Explanation

Cooling a fixed mass of gas reduces the average kinetic energy of its particles, so they hit the walls less often and with less force and the pressure inside the bottle falls. The greater atmospheric pressure outside then pushes the flexible bottle inwards until the pressures balance. The number and size of the particles do not change.

Question 11Matter and its importance / Jirim dan kepentingannya

In a solid, the particles are held in fixed positions but can vibrate about those positions. Which property of solids is best explained by this particle arrangement?

  1. Solids mix rapidly with water to form a solution.
  2. Solids have a fixed shape and are difficult to compress. Correct answer.
  3. Solids expand to fill the whole space available.
  4. Solids have a fixed volume but flow to take the shape of their container.

Explanation

Fixed particle positions give a solid a definite shape and volume, and the closely packed particles leave little empty space, so a solid resists compression. The particles vibrate but do not move from place to place.

Question 12Matter and its importance / Jirim dan kepentingannya

Fine smoke particles suspended in air are observed through a microscope and seen to move in a random, zig-zag path. What causes this motion?

  1. Repulsion between the smoke particles themselves.
  2. Unequal collisions of air molecules with the smoke particles. Correct answer.
  3. Steady convection currents circulating through the air.
  4. The smoke particles dissolving in the air.

Explanation

The smoke particles are struck unevenly by fast-moving air molecules, so the resultant force on a particle changes direction at random. This is Brownian motion and provides evidence for the random motion of particles in a gas.

Question 13Matter and its importance / Jirim dan kepentingannya

Which of the following substances is a mixture?

  1. Air Correct answer.
  2. Sodium chloride
  3. Distilled water
  4. Carbon dioxide

Explanation

A mixture contains two or more substances that are not chemically combined. Air contains nitrogen, oxygen, argon, carbon dioxide and other gases mixed together, so it is a mixture.

Question 14Matter and its importance / Jirim dan kepentingannya

A student wants to obtain pure copper(II) sulphate crystals from a saturated aqueous solution. Which procedure is most suitable?

  1. Filter the solution through filter paper, then heat the filtrate until it boils to dryness.
  2. Heat the solution to dryness in an evaporating dish, then scrape out the solid.
  3. Add more water to the solution, then evaporate it completely over a Bunsen flame.
  4. Cool the saturated solution, filter off the crystals, and rinse them with a little cold distilled water. Correct answer.

Explanation

Crystallisation relies on the solubility of copper(II) sulphate decreasing as the solution cools, so crystals form and can be filtered off. Rinsing with a little cold distilled water removes mother liquor without dissolving much of the product.

Question 15Matter and its importance / Jirim dan kepentingannya

In paper chromatography, a mixture of three coloured dyes is separated on paper with a suitable solvent. The dye spot that travels the greatest distance up the paper is the one that is

  1. made of the largest molecules in the mixture.
  2. least dense among the three dyes.
  3. least soluble in the solvent and most strongly attracted to the paper.
  4. most soluble in the solvent and least strongly attracted to the paper. Correct answer.

Explanation

In paper chromatography the solvent is the mobile phase and the water held on the paper is the stationary phase. A dye that dissolves readily in the solvent and is only weakly adsorbed on the paper is carried furthest, giving the largest Rf value.

Question 16Matter and its importance / Jirim dan kepentingannya

A mixture of cooking oil and water is shaken vigorously and then left to stand. Which method and reason are most suitable for separating the two liquids?

  1. Fractional distillation, because the two liquids have different boiling points.
  2. Use a separating funnel, because oil and water are immiscible and form two layers. Correct answer.
  3. Evaporate the mixture, because water changes to steam first.
  4. Filter through filter paper, because the oil is trapped in the paper.

Explanation

Oil and water are immiscible, so on standing they form two layers with the less dense oil on top. A separating funnel allows the lower aqueous layer to be run off first, after which the oil can be collected.

Question 17Matter and its importance / Jirim dan kepentingannya

Cotton wool soaked in concentrated ammonia solution and cotton wool soaked in concentrated hydrochloric acid are placed at opposite ends of a long horizontal glass tube. White fumes appear nearer to the hydrochloric acid end. Which statement explains this observation?

  1. Hydrogen chloride molecules diffuse faster because hydrochloric acid is a stronger acid.
  2. The white fumes form only when the tube is warmed, so the gases meet at the acid end.
  3. Ammonia molecules diffuse faster than hydrogen chloride molecules because ammonia has a lower relative molecular mass. Correct answer.
  4. Ammonia molecules are heavier than hydrogen chloride molecules, so they diffuse more slowly through the tube.

Explanation

At the same temperature, lighter molecules have higher average speeds, so ammonia (Mr = 17) diffuses faster than hydrogen chloride (Mr = 36.5). They therefore meet and form white ammonium chloride fumes closer to the hydrochloric acid end.

Question 18Matter and its importance / Jirim dan kepentingannya

Solid sodium chloride does not conduct electricity, but molten sodium chloride does. Which explanation is correct?

  1. In the solid, electrons are localized in covalent bonds; when molten, the electrons become free to move.
  2. Sodium chloride decomposes into neutral atoms when it melts.
  3. Melting changes the covalent bonds in sodium chloride into ionic bonds.
  4. In the solid, ions are held in fixed lattice positions; when molten, the ions are free to move. Correct answer.

Explanation

Sodium chloride is an ionic compound. In the solid the ions are locked in a lattice and cannot move, but on melting the lattice breaks down and the mobile ions carry charge through the liquid.

Question 19Matter and its importance / Jirim dan kepentingannya

A fixed mass of gas is compressed at constant temperature until its volume is halved. Which statement best explains why the pressure doubles?

  1. The particles themselves become smaller when the gas is compressed.
  2. The particles move faster because the temperature is constant and the gas is compressed into a smaller space.
  3. The mass of each gas particle increases as the volume decreases.
  4. The number of particles per unit volume doubles, so collisions with the container walls become more frequent. Correct answer.

Explanation

At constant temperature the average kinetic energy and speed of the particles stay the same. Halving the volume doubles the number of particles in each unit of volume, so the particles strike the walls twice as often and the pressure doubles.

Question 20Matter and its importance / Jirim dan kepentingannya

At the top of a mountain, pure water boils at about 90 °C instead of 100 °C. Which explanation is correct?

  1. The boiling point of water is fixed at 100 °C, so the thermometer must be faulty.
  2. The latent heat of vaporisation of water decreases at high altitude.
  3. The water molecules have less kinetic energy at high altitude because the surrounding air is colder.
  4. Lower atmospheric pressure means less energy is needed for molecules to escape as gas. Correct answer.

Explanation

Boiling occurs when the saturated vapour pressure of the liquid equals the external atmospheric pressure. At high altitude the atmospheric pressure is lower, so this equality is reached at a lower temperature.

Question 21Matter and its importance / Jirim dan kepentingannya

The nuclide notation for a chlorine atom is written as ³⁷₁₇Cl. How many neutrons are there in one atom of this nuclide?

  1. 20 Correct answer.
  2. 17
  3. 54
  4. 37

Explanation

The nucleon number (37) is the total number of protons and neutrons, while the proton number (17) is the number of protons. The number of neutrons is therefore 37 − 17 = 20. The 17 electrons are not involved in this subtraction because they are not nucleons.

Question 22Matter and its importance / Jirim dan kepentingannya

Which statement correctly describes the arrangement and movement of particles in a liquid?

  1. The particles are closely packed in an ordered pattern and only vibrate about fixed positions.
  2. The particles are far apart but held in fixed positions by strong forces between them.
  3. The particles are very far apart and move rapidly in random directions with almost no attraction between them.
  4. The particles are closely packed in a random arrangement and are able to slide past one another. Correct answer.

Explanation

In a liquid the particles are still close together and attracted to each other, but the arrangement is irregular rather than ordered. Because the forces are not strong enough to lock them in place, the particles can slide over one another, which is why a liquid flows and takes the shape of its container.

Question 23Matter and its importance / Jirim dan kepentingannya

An atom of an element has 7 protons. In which group of the Modern Periodic Table is this element placed?

  1. Group 17
  2. Group 1
  3. Group 2
  4. Group 15 Correct answer.

Explanation

A neutral atom with 7 protons has 7 electrons, arranged in shells as 2.5. The group number is determined by the number of electrons in the outermost occupied shell, so five valence electrons place the element in Group 15.

Question 24Matter and its importance / Jirim dan kepentingannya

Four gases are kept at the same temperature and pressure in identical containers. Which gas diffuses most rapidly through a small hole in its container?

  1. Nitrogen, N₂
  2. Oxygen, O₂
  3. Hydrogen, H₂ Correct answer.
  4. Carbon dioxide, CO₂

Explanation

At the same temperature, all gas molecules have the same average kinetic energy, so a molecule with a smaller mass must travel faster. Hydrogen has the smallest relative molecular mass (2), so its molecules have the highest average speed and diffuse most rapidly.

Question 25Matter and its importance / Jirim dan kepentingannya

A fixed mass of gas occupies 200 cm³ at 27 °C. It is heated at constant pressure until its volume becomes 300 cm³. What is the final temperature of the gas?

  1. 40.5 °C
  2. 450 °C
  3. 18 °C
  4. 177 °C Correct answer.

Explanation

Temperatures must first be converted to kelvin: 27 °C = 300 K. At constant pressure, volume is directly proportional to absolute temperature, so T₂ = 300 K × (300 ÷ 200) = 450 K. Converting back to degrees Celsius gives 450 − 273 = 177 °C.

Question 26Atomic structure / Struktur atom

The proton number of an atom is equal to the number of which particle?

  1. Nucleons
  2. Neutrons
  3. Protons Correct answer.
  4. Electrons

Explanation

Proton number (atomic number) is defined as the number of protons in the nucleus of an atom. For a neutral atom it also equals the number of electrons, but the defining particle is the proton. Neutrons and nucleons are counted by the nucleon number instead.

Question 27Atomic structure / Struktur atom

A chlorine atom has proton number 17. What is the electron arrangement of the chlorine atom?

  1. 2.8.6
  2. 2.7.8
  3. 2.8.8
  4. 2.8.7 Correct answer.

Explanation

A neutral chlorine atom has 17 electrons, which fill the shells in the order 2, then 8, then 7. The third shell is filled only after the first two shells are complete. This gives the arrangement 2.8.7, with seven valence electrons.

Question 28Atomic structure / Struktur atom

Which statement defines isotopes?

  1. Atoms of the same element that have different numbers of electrons
  2. Atoms of different elements that share the same number of neutrons
  3. Atoms of different elements that share the same nucleon number
  4. Atoms of the same element that have different numbers of neutrons Correct answer.

Explanation

Isotopes are atoms of the same element, so they have identical proton numbers, but they contain different numbers of neutrons. Because the neutron number differs, their nucleon numbers also differ. A change in electron number produces an ion, not an isotope.

Question 29Atomic structure / Struktur atom

A potassium atom is represented by the symbol ³⁹₁₉K. What is the number of neutrons in this atom?

  1. 39
  2. 58
  3. 19
  4. 20 Correct answer.

Explanation

The lower number (19) is the proton number and the upper number (39) is the nucleon number. Neutron number is found by subtracting proton number from nucleon number, giving 39 minus 19 equals 20. The 19 electrons are not part of the nucleus and are not counted.

Question 30Atomic structure / Struktur atom

An atom of element X has the electron arrangement 2.8.1. In which group of the Periodic Table is element X placed?

  1. Group 17
  2. Group 2
  3. Group 1 Correct answer.
  4. Group 18

Explanation

For a main-group element, the group number is given by the number of electrons in the outermost shell. Element X has one electron in its third shell, so it belongs to Group 1. Atoms with a single valence electron lose it readily to form 1+ ions.

Question 31Atomic structure / Struktur atom

The sulphide ion is written as S²⁻ and the sulphur atom has proton number 16. What is the number of electrons in the sulphide ion?

  1. 34
  2. 18 Correct answer.
  3. 14
  4. 16

Explanation

A sulphur atom contains 16 electrons because its proton number is 16. The 2− charge shows that the atom has gained two electrons, so the ion contains 16 plus 2 equals 18 electrons. Gaining electrons does not change the proton number.

Question 32Atomic structure / Struktur atom

Chlorine consists of 75% of the isotope ³⁵Cl and 25% of the isotope ³⁷Cl. What is the relative atomic mass of chlorine?

  1. 35.0
  2. 36.0
  3. 37.0
  4. 35.5 Correct answer.

Explanation

Relative atomic mass is the weighted average of the isotopic masses according to their abundances. The calculation is (75 × 35 + 25 × 37) divided by 100, which gives 35.5. This is why the relative atomic mass of chlorine is not a whole number.

Question 33Atomic structure / Struktur atom

Which statement about the nucleus of an atom is correct?

  1. It contains only neutrons and carries no charge at all.
  2. It contains protons and electrons and is negatively charged.
  3. It contains protons and neutrons and holds most of the mass. Correct answer.
  4. It occupies most of the volume of the atom and is neutral.

Explanation

The nucleus contains protons and neutrons, whose masses are concentrated in a tiny central region. Because protons are positive and neutrons are uncharged, the nucleus is positively charged overall. Electrons move in the shells outside the nucleus.

Question 34Atomic structure / Struktur atom

An ion M³⁺ has the electron arrangement 2.8. What is the proton number of atom M?

  1. 16
  2. 10
  3. 7
  4. 13 Correct answer.

Explanation

The arrangement 2.8 shows the ion has 10 electrons. The 3+ charge means the neutral atom has three electrons more than the ion, so the atom has 13 electrons. Since the atom is neutral, its proton number is also 13.

Question 35Atomic structure / Struktur atom

Four particles are described. P: 17 protons, 18 neutrons, 17 electrons. Q: 17 protons, 20 neutrons, 17 electrons. R: 18 protons, 17 neutrons, 18 electrons. S: 17 protons, 18 neutrons, 18 electrons. Which two particles are isotopes of the same element?

  1. P and Q Correct answer.
  2. P and S
  3. Q and R
  4. R and S

Explanation

Isotopes are atoms of the same element, meaning equal proton numbers, that differ in neutron number. P and Q both have 17 protons but 18 and 20 neutrons respectively, so they are isotopes of chlorine. P and S differ only in electrons, so they are the same atom and its ion.

Question 36Atomic structure / Struktur atom

Which row correctly describes a neutron?

  1. Relative mass 1, charge +1
  2. Relative mass 1, charge 0 Correct answer.
  3. Relative mass 1/1836, charge −1
  4. Relative mass 1/1836, charge 0

Explanation

A neutron is a neutral particle found in the nucleus. Its relative mass is about 1, while an electron has a relative mass of about 1/1836 and a charge of −1.

Question 37Atomic structure / Struktur atom

The nucleon number of an atom is the total number of which particles?

  1. Protons and electrons
  2. Neutrons only
  3. Protons only
  4. Protons and neutrons Correct answer.

Explanation

The nucleon number, also called the mass number, counts all particles in the nucleus. It is the sum of protons and neutrons, so electrons are not included.

Question 38Atomic structure / Struktur atom

What is the maximum number of electrons that can occupy the second shell of an atom?

  1. 2
  2. 8
  3. 18 Correct answer.
  4. 32

Explanation

The nth shell can hold a maximum of 2n² electrons. For the second shell, n = 2, so 2 × 2² = 8; the first shell holds only 2.

Question 39Atomic structure / Struktur atom

Two isotopes of the same element have identical chemical properties because they have the same

  1. same relative atomic mass
  2. same electron arrangement Correct answer.
  3. same neutron number in the nucleus
  4. same nucleon number of each atom

Explanation

Chemical properties depend mainly on the number and arrangement of electrons, especially the valence electrons. Isotopes of an element have the same proton and electron numbers but different neutron numbers.

Question 40Atomic structure / Struktur atom

A particle contains 12 protons, 12 neutrons and 10 electrons. What is its charge?

  1. 2−
  2. 12+
  3. 2+ Correct answer.
  4. 0

Explanation

Charge is found from protons minus electrons: 12 − 10 = +2. Neutrons are neutral and do not affect the charge.

Question 41Atomic structure / Struktur atom

An atom of element X has the electron arrangement 2.8.7. What is the charge of the ion that X forms most readily?

  1. 7−
  2. 1+
  3. 1− Correct answer.
  4. 2−

Explanation

An atom with arrangement 2.8.7 has seven valence electrons. It gains one electron to complete the outer shell, forming an ion with one negative charge.

Question 42Atomic structure / Struktur atom

The relative atomic mass of an element is defined as the average mass of its atoms compared with

  1. mass of one hydrogen atom
  2. mass of one proton
  3. 1/12 of a carbon-12 atom Correct answer.
  4. mass of one carbon-12 atom

Explanation

Relative atomic mass compares the average mass of an element's atoms with one-twelfth of the mass of a carbon-12 atom. The carbon-12 scale is the standard used in chemistry.

Question 43Atomic structure / Struktur atom

A fluoride ion, F⁻, has proton number 9. Which particle has the same electron arrangement as F⁻?

  1. Neon atom Correct answer.
  2. Oxygen atom
  3. Chlorine atom
  4. Magnesium atom

Explanation

The fluoride ion F⁻ has 9 + 1 = 10 electrons. A neutral neon atom also has 10 electrons, so the two species are isoelectronic.

Question 44Atomic structure / Struktur atom

A particle has 20 protons, 20 neutrons and 18 electrons. Which species is represented?

  1. K⁺
  2. Ca²⁺ Correct answer.
  3. Ca²⁻
  4. Ar

Explanation

The 20 protons identify the element as calcium. With 18 electrons, the particle has two fewer electrons than protons, giving a 2+ charge.

Question 45Atomic structure / Struktur atom

An ion E²⁻ has the electron arrangement 2.8.8. What is the proton number of atom E?

  1. 16 Correct answer.
  2. 14
  3. 20
  4. 18

Explanation

The ion E²⁻ has 18 electrons because 2.8.8 totals 18. A 2− ion has two more electrons than protons, so the proton number is 18 − 2 = 16.

Question 46Atomic structure / Struktur atom

Which scientist proposed that electrons move around the nucleus in fixed shells or energy levels?

  1. J. J. Thomson
  2. Ernest Rutherford
  3. Niels Bohr Correct answer.
  4. John Dalton

Explanation

Niels Bohr proposed in 1913 that electrons move around the nucleus in fixed shells or energy levels. Dalton described atoms as solid spheres, Thomson proposed the plum-pudding model, and Rutherford concluded that a small positive nucleus exists. Bohr's model introduced quantised electron shells.

Question 47Atomic structure / Struktur atom

An atom has the electron arrangement 2.8.5. How many electrons are in its outermost shell?

  1. 8
  2. 15
  3. 3
  4. 5 Correct answer.

Explanation

The outermost shell is the last occupied shell in the electron arrangement. In 2.8.5 the third shell contains 5 electrons, so there are 5 valence electrons. The numbers 3 and 8 refer to the number of shells and the second-shell occupancy, while 15 is the total number of electrons.

Question 48Atomic structure / Struktur atom

An atom of element X has the electron arrangement 2.8.2. What is the electron arrangement of the ion X²⁺?

  1. 2.8 Correct answer.
  2. 2.8.4
  3. 2.8.2
  4. 2.8.8

Explanation

An atom with electron arrangement 2.8.2 has two valence electrons and forms X²⁺ by losing these two electrons. Removing two electrons from the third shell leaves the arrangement 2.8, which is the stable neon configuration. No electrons are added, and the inner shells are unchanged.

Question 49Atomic structure / Struktur atom

An atom of element Y has the electron arrangement 2.8.6. In which period of the Periodic Table is element Y located?

  1. Period 6
  2. Period 3 Correct answer.
  3. Period 16
  4. Period 2

Explanation

The period number equals the number of occupied electron shells in an atom. The arrangement 2.8.6 has electrons in three shells, so element Y is in Period 3. The valence-shell value 6 shows it is in Group 16, not Period 16.

Question 50Atomic structure / Struktur atom

A sample of element Q consists of two isotopes, ⁶³Q and ⁶⁵Q. The relative atomic mass of Q is 63.6. What is the percentage abundance of ⁶⁵Q?

  1. 40%
  2. 30% Correct answer.
  3. 20%
  4. 70%

Explanation

Let the percentage abundance of ⁶⁵Q be x. Then 63(100 − x) + 65x = 63.6 × 100, which simplifies to 6300 + 2x = 6360, so x = 30. Therefore ⁶⁵Q is 30% abundant and ⁶³Q is 70% abundant.