AQA GCSE Combined Science Foundation (8464), Foundation tier · Chemistry › Atomic structure and the periodic table › The periodic table
Practise The periodic table. 6 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
How the modern periodic table is arranged (by atomic number, in groups and periods), and why elements in the same group have similar chemical properties. You also need to predict an element's reactions from its position.
Key facts
Order: increasing atomic (proton) number
Group: vertical column; same number of outer electrons; similar chemical properties
Period: horizontal row; same number of occupied shells
Group number = number of outer electrons (Groups 1 to 7)
Group 0: full outer shell
'Periodic': similar properties repeat at regular intervals
Notes
How the table is arranged
diagram
The elements are arranged in order of atomic (proton) number.
Elements with similar properties are in the same vertical column, called a group.
The horizontal rows are called periods.
Groups are columns (Group 1 in blue). Periods are rows (period 3 in red).
It is called the periodic table because similar properties occur at regular intervals as the atomic number increases.
Groups and electrons
Elements in the same group have the same number of electrons in their outer shell.
Chemical reactions depend on the outer electrons, so elements in the same group have similar chemical properties.
For Groups 1 to 7, the group number = the number of outer electrons. Group 0 elements have a full outer shell.
The period number = the number of occupied shells.
So an element's position depends on the arrangement of its electrons, which depends on its atomic number.
Making predictions
Use the group to predict the type of reaction: rubidium is in Group 1, so, like sodium, it reacts with water to form an alkaline hydroxide and hydrogen.
Use the trend down the group to predict reactivity: Group 1 elements get more reactive down the group; Group 7 elements get less reactive.
Metals are on the left and towards the bottom of the table; non-metals are on the right and towards the top.
How to answer each type of question
Recall how the periodic table is arranged
1 mark eachGrade 4
Ordered by atomic number (proton number), not by mass.
Columns are groups; rows are periods.
Example. (a) Complete the sentence: the elements in the modern periodic table are arranged in order of ...... (b) What name is given to a vertical column of the periodic table?
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(a) atomic number / proton number (1) (not 'atomic mass') (b) group (1)
Explain why elements in a group have similar properties
2 marksGrade 5
State the number of outer electrons they all have.
Say that chemical properties depend on the outer electrons.
Example. Lithium, sodium and potassium react with water in similar ways. Explain why, in terms of electrons.
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They all have one electron in their outer shell (1). The reactions of an element depend on its outer electrons, so they react in similar ways (1).
Don’t lose marks
Saying the modern table is arranged by atomic mass or atomic weight. That was how the early tables were arranged.
Saying elements in a group have the same number of electrons. They have the same number of outer electrons.
Mixing up groups (columns) and periods (rows).
Saying elements in a group have the same properties. Their properties are similar and change gradually down the group.
More tips
Memory tricks
Periods run across, like lines of writing on a page; groups run down, like columns in a newspaper.
Group = number of outer electrons; period = number of shells.
Same group → same number of outer electrons → same kind of reactions.
Exam technique
In 'explain' questions, the key phrase is 'the same number of electrons in the outer shell'.
When predicting, give the prediction and the pattern it is based on.
Use the periodic table on the data sheet: it gives the atomic number and relative atomic mass of every element.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
Identify groups and periodsGroups are the vertical columns; periods are the horizontal rows.
Grade 4
State how the elements are orderedIn order of atomic (proton) number.
Grade 5
Explain why group members react similarlyThey have the same number of electrons in their outer shell.
Grade 5
Link position to electronic structureGroup number = outer electrons (Groups 1 to 7); period = number of occupied shells.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Give the number of occupied energy levels (shells) and the number of outer-shell electrons in a calcium atom.
4 occupied shells; 2 outer-shell electrons
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
The modern periodic table contains more than 100 elements.
(a) Complete the sentence. Tick (✓) one box. The elements in the periodic table are arranged in order of ................[1]
atomic number
mass number
number of neutrons
relative atomic mass
(b) What name is given to a vertical column of elements in the periodic table?[1]
(c) Why do elements in the same vertical column of the periodic table have similar chemical properties?[1]
(d) Why is the table called a periodic table?[1]
Show the answer and mark scheme
(a)Answer: atomic number
(b)Answer: a group
group
(c)Answer: Their atoms have the same number of electrons in the outer shell.
(atoms have the) same number of electrons in the outer shell / energy level
(d)Answer: Similar properties occur at regular intervals.
similar properties occur at regular intervals
Question 2Medium4 marks
Calcium is in Period 4 and Group 2 of the periodic table.
(a) Give the number of occupied energy levels (shells) and the number of outer-shell electrons in a calcium atom.[2]
(b) Use this information to give the electronic structure of a calcium atom.[1]