GCSE ChemistryAQA, Edexcel and OCR
40 chemistry questions on atoms and the periodic table. Pick your answer, then tap to see if you were right and why. Every answer comes from the Show Working science bank, checked against the GCSE content every board in England teaches.
01 / Quiz yourselfTry it, then tap to check
Choose your answer before you open it. Then read why, so it sticks.
01 / Atoms and the periodic tableBoth tiers
Answer: B In the nucleus
An atom has a tiny, positively charged nucleus at its centre, made of protons and neutrons. Almost all of the mass is there. Negatively charged electrons move around the nucleus in shells.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.1.5 Size and mass of atoms
02 / Atoms and the periodic tableBoth tiers
Answer: C It is far smaller
The radius of the nucleus is tiny compared with the radius of the atom: less than a ten-thousandth of it. So most of an atom is empty space, with electrons moving around the nucleus.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.1.5 Size and mass of atoms
03 / Atoms and the periodic tableBoth tiers
Answer: A It has equal numbers of protons and electrons
Each proton has a charge of +1 and each electron a charge of −1. An atom has the same number of electrons as protons, so the charges cancel and the atom is neutral.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.1.4 Relative electrical charges of subatomic particles
04 / Atoms and the periodic tableBoth tiers
Answer: B About 1 × 10⁻¹⁰ m
Atoms are very small: a typical atom has a radius of about 0.1 nm, which is 1 × 10⁻¹⁰ m. Small molecules, made of only a few atoms, are of a similar order of size.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.1.5 Size and mass of atoms
05 / Atoms and the periodic tableBoth tiers
Answer: D An atom
Atoms and the bonds between them are around 10⁻¹⁰ m. Even a bacterium, about 10⁻⁶ m long, is thousands of times bigger, so anything you can see contains millions of atoms.
Checked against OCR Gateway Chemistry A J248 specification, C1.2c Atomic structure
06 / Atoms and the periodic tableBoth tiers
Answer: B Tiny spheres that could not be divided
Early models showed atoms as tiny solid spheres that could not be broken into anything smaller. The discovery of the electron showed that atoms contain even smaller particles, so the model had to change.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.1.3 The development of the model of the atom
07 / Atoms and the periodic tableBoth tiers
Answer: B A ball of positive charge with electrons in it
When the electron was discovered, scientists knew atoms held negative particles. The plum pudding model pictured the atom as a ball of positive charge with negative electrons embedded in it, like fruit in a pudding.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.1.3 The development of the model of the atom
08 / Atoms and the periodic tableBoth tiers
Answer: D Most of the atom is empty space
Most alpha particles passed straight through, so the atom is mostly empty space. A few were deflected or bounced back, so the mass and positive charge must be packed into a tiny centre: the nucleus. This nuclear model replaced the plum pudding model.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.1.3 The development of the model of the atom
09 / Atoms and the periodic tableBoth tiers
Answer: A The positive charge is in a tiny nucleus
In the plum pudding model the positive charge fills the whole atom. In the nuclear model the positive charge and almost all the mass are in a tiny nucleus, with electrons outside it and empty space between.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.1.3 The development of the model of the atom
10 / Atoms and the periodic tableBoth tiers
Answer: B New experimental evidence does not fit it
First atoms were pictured as tiny spheres that could not be divided. The discovery of the electron led to the plum pudding model, and alpha scattering led to the nuclear model. Each time, new evidence led scientists to change or replace the model.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.1.3 The development of the model of the atom
11 / Atoms and the periodic tableBoth tiers
Answer: C Proton
Protons have a relative charge of +1, electrons −1, and neutrons 0. The protons give the nucleus its positive charge; the neutrons add mass but no charge.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.1.4 Relative electrical charges of subatomic particles
12 / Atoms and the periodic tableBoth tiers
Answer: A Neutron
Protons and neutrons each have a relative mass of 1. An electron has a very small mass, about 2000 times less than a proton, which is why almost all the mass of an atom is in the nucleus.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.1.5 Size and mass of atoms
13 / Atoms and the periodic tableBoth tiers
Answer: C The number of protons
The atomic number is the number of protons in the nucleus. Every atom of an element has the same number of protons, and no other element has that number, so it identifies the element.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.1.4 Relative electrical charges of subatomic particles
14 / Atoms and the periodic tableBoth tiers
Answer: B The number of protons plus neutrons
The mass number counts the protons and neutrons together. Taking away the atomic number (the protons) leaves the number of neutrons. In an atom, the number of electrons equals the number of protons.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.1.5 Size and mass of atoms
15 / Atoms and the periodic tableBoth tiers
Answer: C The mass number
An atom is written with its symbol, the mass number at the top left and the atomic number at the bottom left. For sodium-23 that is 23 on top and 11 underneath. The mass number is never smaller than the atomic number.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.1.5 Size and mass of atoms
16 / Atoms and the periodic tableBoth tiers
Answer: C Atoms of an element with different numbers of neutrons
Isotopes are atoms of the same element, so they have the same number of protons, but they have different numbers of neutrons. That gives them different mass numbers.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.1.5 Size and mass of atoms
17 / Atoms and the periodic tableBoth tiers
Answer: B It loses electrons
Ions form when atoms lose or gain electrons. The nucleus does not change. Losing electrons leaves more protons than electrons, so the ion is positive; gaining electrons makes it negative.
Checked against OCR Gateway Chemistry A J248 specification, C1.2e Atomic structure
18 / Atoms and the periodic tableBoth tiers
Answer: A Two fewer electrons than protons
The charge on an ion tells you the difference between protons and electrons. A 2+ ion has two fewer electrons than protons; a 2− ion has two more. The number of protons stays the same as in the atom.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.1.5 Size and mass of atoms
19 / Atoms and the periodic tableBoth tiers
Answer: B Increasing atomic number
The modern table lists elements in order of atomic (proton) number. Rows are periods and columns are groups. Similar properties come up at regular intervals, which is why it is called periodic.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.2.1 The periodic table
20 / Atoms and the periodic tableBoth tiers
Answer: D The same number of outer electrons
For Groups 1 to 7 the group number is the number of electrons in the outer shell. The period number is the number of shells that contain electrons. So an element’s position comes from its electron arrangement, which comes from its atomic number.
Checked against OCR Gateway Chemistry A J248 specification, C2.2c Bonding
21 / Atoms and the periodic tableBoth tiers
Answer: C Period 3, Group 7
The number of shells gives the period and the number of outer electrons gives the group. An element with 2, 8 and 1 electrons in its shells has one outer electron, so it is in Group 1 (it is sodium).
Checked against AQA GCSE Chemistry 8462 specification, 4.1.1.7 Electronic structure
22 / Atoms and the periodic tableBoth tiers
Answer: B 2
Electrons occupy the lowest energy levels first, which are the shells closest to the nucleus. For the first 20 elements, the first shell holds up to 2 electrons and the next two shells up to 8 each.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.1.7 Electronic structure
23 / Atoms and the periodic tableBoth tiers
Answer: A For elements not yet discovered
Mendeleev left gaps where no known element fitted the pattern. He predicted the properties of the missing elements, and when elements with those properties were found, the gaps were filled and his table was accepted.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.2.2 Development of the periodic table
24 / Atoms and the periodic tableBoth tiers
Answer: B So elements with similar properties lined up
In a few places, strict atomic weight order put elements in the wrong group, so Mendeleev swapped them. We now know the order is by atomic number. Isotopes explain the swaps: tellurium has heavy isotopes, so its average mass is higher, but it has fewer protons than iodine.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.2.2 Development of the periodic table
25 / Atoms and the periodic tableBoth tiers
The right order:
Early tables used atomic weight alone and put some elements in the wrong groups. Mendeleev fixed this with gaps and swaps. Later discoveries filled the gaps, and knowing about protons and isotopes explained why his order was right.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.2.2 Development of the periodic table
26 / Atoms and the periodic tableBoth tiers
Answer: A K
Some symbols come from old Latin names: K for potassium (kalium), Na for sodium (natrium) and Fe for iron (ferrum). A symbol has one capital letter, sometimes followed by a small letter.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.1.1 Atoms, elements and compounds
27 / Atoms and the periodic tableBoth tiers
Answer: C Cl₂
Hydrogen, oxygen, nitrogen and the halogens exist as molecules of two atoms: H₂, O₂, N₂, Cl₂, Br₂, I₂. Writing Cl or Br for the element in an equation is a common mistake.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.2.6 Group 7
28 / Atoms and the periodic tableBoth tiers
Answer: B MgCl₂
In an ionic compound the charges must cancel. Mg²⁺ needs two Cl⁻ ions, so magnesium chloride is MgCl₂. O²⁻ needs two Na⁺ ions, so sodium oxide is Na₂O.
Checked against AQA GCSE Chemistry 8462 specification, 4.2.1.2 Ionic bonding
29 / Atoms and the periodic tableBoth tiers
Answer: B 2Na + Cl₂ → 2NaCl
A balanced equation has the same number of each kind of atom on both sides, and uses correct formulae: chlorine and hydrogen are Cl₂ and H₂. You balance by changing the big numbers in front, never the formulae.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.1.1 Atoms, elements and compounds
30 / Atoms and the periodic tableBoth tiers
Answer: A It is lost, making a positive ion
Atoms react to get a full outer shell. A Group 1 atom has one outer electron, which it loses to form a 1+ ion. A Group 7 atom has seven, so it gains one electron from a metal to form a 1− ion.
Checked against AQA GCSE Chemistry 8462 specification, 4.2.1.2 Ionic bonding
31 / Atoms and the periodic tableBoth tiers
Answer: C Sodium hydroxide and hydrogen
Group 1 metals react with water to give a metal hydroxide and hydrogen gas. The hydroxide dissolves to make an alkaline solution, which is why they are called the alkali metals.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.2.5 Group 1
32 / Atoms and the periodic tableBoth tiers
Answer: A It fizzes and bursts into a lilac flame
Lithium, sodium and potassium all float and fizz as hydrogen forms. Lithium fizzes steadily, sodium melts into a ball and whizzes around, and potassium reacts so quickly that the hydrogen ignites, giving a lilac flame.
Checked against Pearson Edexcel GCSE Chemistry 1CH0 specification, 6.3 Groups in the periodic table
33 / Atoms and the periodic tableBoth tiers
Answer: A Soft metals with low melting points
Group 1 metals are soft enough to cut with a knife and have low melting points for metals. They react quickly with oxygen and water, so they are kept under oil. A freshly cut surface is shiny but soon goes dull.
Checked against Pearson Edexcel GCSE Chemistry 1CH0 specification, 6.2 Groups in the periodic table
34 / Atoms and the periodic tableBoth tiers
Answer: B Sodium chloride
Group 1 metals react with chlorine to form white metal chlorides, and with oxygen to form metal oxides. These are ionic compounds containing 1+ metal ions.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.2.5 Group 1
35 / Atoms and the periodic tableBoth tiers
Answer: D It increases
Group 1 metals get more reactive down the group: potassium reacts more violently than sodium. The halogens get less reactive down Group 7: fluorine is the most reactive and iodine is less reactive than bromine.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.2.5 Group 1
36 / Atoms and the periodic tableBoth tiers
Answer: B They increase
The halogens are non-metals that exist as molecules of two atoms (Cl₂, Br₂, I₂). Further down the group the molecules are bigger and heavier, so their melting and boiling points are higher.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.2.6 Group 7
37 / Atoms and the periodic tableBoth tiers
Answer: D Chlorine and potassium bromide solution
A more reactive halogen displaces a less reactive one from a solution of its salt. Chlorine displaces bromine and iodine; bromine displaces iodine; iodine displaces neither. A less reactive halogen cannot push out a more reactive one.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.2.6 Group 7
38 / Atoms and the periodic tableBoth tiers
Answer: C An ionic salt
With metals, halogens gain electrons and form ionic compounds such as sodium chloride. With non-metals such as hydrogen, they share electrons and form covalent molecules such as hydrogen chloride (HCl).
Checked against AQA GCSE Chemistry 8462 specification, 4.1.2.6 Group 7
39 / Atoms and the periodic tableBoth tiers
Answer: B Unreactive gases made of single atoms
The noble gases are colourless gases made of single atoms. They are very unreactive and do not easily form molecules. Their boiling points rise down the group as relative atomic mass increases.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.2.4 Group 0
40 / Atoms and the periodic tableBoth tiers
Answer: A They have a full outer shell of electrons
Noble gas atoms already have stable, full outer shells, so they have no need to lose, gain or share electrons. Most have eight outer electrons; helium has only two, which fills its first shell.
Checked against AQA GCSE Chemistry 8462 specification, 4.1.2.4 Group 0
02 / Longer answersMarked by levels
Write your answer first, on paper. Then open it and tick off the points you made. How 6-mark questions are marked.
6 marks / Reactivity of the alkali metalsBoth tiers
A teacher drops small pieces of lithium, sodium and potassium, one at a time, into a trough of water with a few drops of universal indicator.
All three metals float on the water, fizz and move around the surface, because they react to give hydrogen gas. Lithium fizzes steadily and slowly gets smaller. Sodium reacts faster: it melts into a silvery ball and whizzes about. Potassium reacts fastest of all and the hydrogen catches fire with a lilac flame. In each trough the universal indicator turns purple, because the other product is a metal hydroxide, such as sodium hydroxide, which dissolves to make an alkaline solution. This shows that reactivity increases down Group 1. Every Group 1 atom has one electron in its outer shell, and when it reacts it loses this electron to form a 1+ ion. Going down the group, the atoms have more shells of electrons, so the outer electron is further from the nucleus and more shielded by the inner electrons. This means the attraction between the positive nucleus and the outer electron is weaker, so the electron is lost more easily, and the metal reacts more vigorously.
Saying the outer electron is “easier to gain” or blaming “more electrons” loses marks. Group 1 atoms lose an electron, and it is the weaker attraction to the nucleus that matters.
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