Section 2: Matter, atomic structure and the periodic table

Write the electron arrangement first, then read the trend from it. Say which particle and which energy level before you explain a property.

A lesson for this section

Quick checks: multiple choice

Question 1 · Both levels

Which describes the particles in a liquid?

Question 2 · Both levels

Under a microscope, specks of smoke in a small cell of air are seen to jiggle about at random. What causes this?

Question 3 · Both levels

Cotton wool soaked in concentrated ammonia is put in one end of a long glass tube, and cotton wool soaked in concentrated hydrochloric acid in the other. A white ring of ammonium chloride forms nearer the acid end. (Mr: NH₃ = 17, HCl = 36.5) Why?

Question 4 · Both levels

When iodine crystals are warmed gently in a beaker, a purple vapour forms and no liquid is seen. What is this change of state called?

Question 5 · Both levels

A forensic chemist wants to find out whether a black ink is a mixture of several dyes. Which technique should she use?

Question 6 · Both levels

Ethanol (boiling point 78 °C) and water (100 °C) mix completely. Which technique separates ethanol from the mixture, and why?

Question 7 · Both levels

Rock salt is a mixture of sodium chloride and sand. Which order of steps gives pure dry sodium chloride?

Question 8 · Both levels

Which of these is a chemical change?

Question 9 · Both levels

When magnesium ribbon is heated strongly in an open crucible, the mass of the solid increases. How is this consistent with the law of conservation of mass?

Question 10 · Higher Level

Which is an assumption of the kinetic theory model of an ideal gas?

Question 11 · Higher Level

The kinetic theory model of an ideal gas cannot explain why steam condenses to water when it is cooled. Which assumption of the model causes this?

Question 12 · Both levels

Which describes the neutron?

Question 13 · Both levels

Chlorine-35 and chlorine-37 are isotopes of chlorine. How do their atoms differ?

Question 14 · Both levels

Aluminium has atomic number 13. How many protons, neutrons and electrons are in one ²⁷Al³⁺ ion?

Question 15 · Both levels

In Rutherford's experiment, most alpha particles passed straight through a thin gold foil, but a very few bounced back. What did the few that bounced back show?

Question 16 · Both levels

A student dips a clean wire loop in an unknown salt and holds it in a blue Bunsen flame. The flame turns lilac. Which metal ion is present?

Question 17 · Both levels

The emission spectrum of the light from a street lamp shows two bright lines very close together in the yellow, at about 589 nm, and little else. Which element is in the lamp?

Question 18 · Both levels

What is the arrangement of electrons in main energy levels in a calcium atom (atomic number 20)?

Question 19 · Both levels

Which ion has the same arrangement of electrons as an argon atom (2, 8, 8)?

Question 20 · Both levels

In the current model of the atom, what is an orbital?

Question 21 · Both levels

Which idea from Bohr's model of the atom is still part of the current model?

Question 22 · Higher Level

Which is the electron configuration of a chromium atom (atomic number 24)?

Question 23 · Higher Level

The 19th electron of a potassium atom goes into the 4s sublevel rather than the 3d. Why?

Question 24 · Higher Level

What is the shape of a p orbital?

Question 25 · Higher Level

Oxygen has the configuration 1s² 2s² 2p⁴. How many unpaired electrons does an oxygen atom have?

Question 26 · Higher Level

The hydrogen spectrum has a series of lines in the ultraviolet. Electrons fall to which energy level to give these lines?

Question 27 · Higher Level

A line in the hydrogen spectrum has a frequency of 6.17 × 10¹⁴ Hz. Taking h as 6.63 × 10⁻³⁴ J s, what is the energy of one photon of this light?

Question 28 · Higher Level

What is meant by an atom in an excited state?

Question 29 · Both levels

Mendeleev left gaps in his periodic table of 1869. Why is this seen as a great strength of his table?

Question 30 · Both levels

In the modern periodic table, in what order are the elements arranged?

Question 31 · Both levels

A small piece of potassium is dropped into a trough of water. What happens?

Question 32 · Both levels

Chlorine water is added to colourless potassium bromide solution and the mixture turns orange. What does this show?

Question 33 · Both levels

Why are the elements of group 18 very unreactive?

Question 34 · Both levels

An element has the electron arrangement 2, 8, 5. Where is it in the periodic table?

Question 35 · Both levels

How does electronegativity change across period 2 from lithium to fluorine?

Question 36 · Both levels

Which halogen is a red-brown liquid at room temperature?

Question 37 · Both levels

Which statement about elements of group 1 and group 17 at room temperature is correct?

Question 38 · Higher Level

Bromine has the configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁵. In which block of the periodic table is it?

Question 39 · Higher Level

The first ionisation energy of aluminium (578 kJ/mol) is lower than that of magnesium (738 kJ/mol). Why?

Question 40 · Higher Level

The first ionisation energy of oxygen (1314 kJ/mol) is lower than that of nitrogen (1402 kJ/mol). Why?

Question 41 · Higher Level

Atomic radius falls across period 3 from sodium to chlorine. Why?

Question 42 · Higher Level

First ionisation energy falls down group 1 from lithium to potassium. Why?

Question 43 · Higher Level

The first ionisation energy of sodium is 496 kJ/mol and the second is 4562 kJ/mol. Why is the second so much larger?

Theory and practical questions

Isotopes of magnesiumWritten question, both levels · 9 marks

Magnesium (atomic number 12) occurs naturally as three isotopes: magnesium-24, magnesium-25 and magnesium-26.

(a) Define the term isotopes. [2]

0 words · one point a mark

(b) How many neutrons are in an atom of magnesium-26? [1]

(d) Explain why the three isotopes of magnesium have the same chemical properties. [2]

0 words · one point a mark

(e) A sample of magnesium chloride may contain some sodium chloride. Describe how a flame test could show whether sodium is present. [3]

0 words · one point a mark

First ionisation energies across period 2Written question, Higher Level · 8 marks

The table shows the first ionisation energies of the elements of period 2, in order of atomic number from 3 to 10.

First ionisation energies of the period 2 elements.
Element	First ionisation energy / kJ/mol
Li	520
Be	899
B	801
C	1086
N	1402
O	1314
F	1681
Ne	2081

(a) Define first ionisation energy. [3]

0 words · one point a mark

(b) Explain why first ionisation energy generally rises across period 2. [2]

0 words · one point a mark

(d) Which element in the table has the largest atomic radius? [1]

Testing the law of conservation of massExperiment and data, both levels · 9 marks

A student tests the law of conservation of mass using 0.50 g of calcium carbonate powder and excess dilute hydrochloric acid. Experiment 1: she weighs an open conical flask holding the acid with a small test tube of the powder standing in it, tips the powder into the acid, and weighs the open flask again when the fizzing stops. Experiment 2: she repeats this inside a plastic bottle with its cap screwed on tightly, and opens the bottle only after the second weighing. Her results are in the table.

Masses before and after reaction.
Experiment	Mass before / g	Mass after / g
1 (open flask)	85.36	85.14
2 (capped bottle)	112.48	112.48

(a) By how many grams did the mass of the open flask fall in experiment 1? [2]

(b) Explain why the mass fell in experiment 1. [2]

0 words · one point a mark

(d) Another student says experiment 1 shows that the law of conservation of mass is wrong. Which reply is best? [1]

(e) Give one hazard in experiment 2 and how to reduce it. [2]

0 words · one point a mark