AQA GCSE Chemistry - 1.2 The Periodic Table - Revision Notes

Sep 5, 2026

AQA GCSE Chemistry revision notes focused on 1.2 The Periodic Table, covering how elements are ordered by increasing atomic number and how this structure groups elements with similar properties. Key ideas explain periods and groups, the atomic number as an element’s identifier, and how valence (outer-shell) electrons connect to predictable reactivity. The notes also introduce the historical development of the table, from early mass-based ordering to Mendeleev’s method and the rationale for gaps.

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Arranging the Elements

How the elements are ordered

Predicting reactions

The atomic number (Examiner Tip)

Periodic (Examiner Tip)

History of the Periodic Table

How was the early Periodic Table arranged?

How did Mendeleev arrange the Periodic Table?

Why are there gaps in Mendeleev's Periodic Table?

Head to www.savemyexams. com for more awesome resources AQA GCSE Chemistry: Combined Science 1 .2 The Periodic Table Contents Arranging the Elements History of the Periodic Table Metals & Non-Metals Group 0: The Noble Gases Group 1: The Alkali Metals Group 7: The Halogens Page 1 of 27 © 2015 − 2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams. com for more awesome resources Arranging the Elements How the elements are ordered There are over 100 chemical elements which have been isolated and identi|ed Elements are arranged on the periodic table in order of increasing atomic number Each element has one proton more than the element preceding it This is done so that elements end up in columns with other elements which have similar properties The table is arranged in vertical columns called groups and in rows called periods Period: These are the horizontal rows that show the number of shells of electrons an atom has and are numbered from 1-7 E. g. elements in Period 2 have two electron shells, elements in Period 3 have three electron shells Group: These are the vertical columns that show how many outer electrons each atom has and are numbered from 1 – 7, with a |nal group called Group 0 (instead of Group 8) E. g. Group 4 elements have atoms with 4 electrons in the outermost shell, Group 6 elements have atoms with 6 electrons in the outermost shell and so on The Periodic Table Page 2 of 27 © 2015 − 2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams. com for more awesome resources The Periodic Table of the Elements Examiner Tip The atomic number is unique to each element and could be considered as an element 's “|ngerprint”. The number of electrons changes during chemical reactions, but the atomic number does not change. Page 3 of 27 © 2015 − 2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams. com for more awesome resources Predicting reactions The group number of an element which is given on the Periodic Table indicates the number of electrons in the outer shell (valence electrons) This rule holds true for all elements except helium; although is in Group 0 , it has only one shell, the |rst and innermost shell, which holds only 2 electrons We can use the group number to predict how elements will react asthe number of valence shell electrons in an element in}uences how the element reacts. Therefore, elements in the same group react similarly By observing the reaction of one element from a group, you can predict how the other elements in that group will react By reacting two or more elements from the same group and observing what happens in those reactions you can make predictions about reactivity and establish trends in reactivity in that group For example, lithium, sodium and potassium are in Group 1 and can all react with elements in Group 7 to forman ionic compound The Group 1 metals become more reactive as you movedown the group while the Group 7 halides show a decrease in reactivity moving down the group Examiner Tip The word “periodic” is used in the name of the Periodic Table as similar properties appear in elements placed at regular intervals throughout the table. Page 4 of 27 © 2015 − 2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams. com for more awesome resources History of the Periodic Table How was the early Periodic Table arranged? Before the discovery of the subatomic particles, scientists arranged the elements in order of their atomic weight and not their atomic number When the elements that were known at that time were sorted by mass into a table, patterns emerged at regular periods along the table, giving rise to the term periodic The earlier tables were incompl

FAQs

How are elements ordered on the periodic table?

Elements are arranged in order of increasing atomic number, so each element has one more proton than the one before it.

What do periods and groups show on the periodic table?

Periods are horizontal rows showing the number of electron shells, while groups are vertical columns showing how many outer electrons atoms have.

How does the periodic table help predict chemical reactions?

The group number indicates the number of valence electrons, so elements in the same group tend to react similarly and show trends in reactivity.

Sep 5, 2026

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