How is the Periodic Table arranged, and what are the trends in Groups 1, 7 and 0?
The arrangement of the Periodic Table into groups and periods, metals and non-metals, and the trends in reactivity in Group 1, Group 7 and Group 0.
A focused answer to the WJEC GCSE Science Double Award Unit 2 topic on the Periodic Table, covering its arrangement into groups and periods, metals and non-metals, and the trends in Group 1 (alkali metals), Group 7 (halogens) and Group 0 (noble gases).
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this dot point is asking
WJEC Double Award Unit 2 wants you to describe how the Periodic Table is arranged, identify metals and non-metals, and explain the reactivity trends in Group 1, Group 7 and Group 0.
The arrangement of the Periodic Table
- Groups are the vertical columns. Elements in the same group have the same number of outer electrons, so they react in similar ways.
- Periods are the horizontal rows. Across a period, the number of outer electrons increases by one each time.
- Metals are on the left and centre; non-metals are on the right. A zig-zag line separates them.
Group 1: the alkali metals
The alkali metals (lithium, sodium, potassium) have 1 outer electron, which they lose to form ions. They are soft, react with water to give hydrogen and an alkaline solution, and become more reactive down the group:
Group 7: the halogens
The halogens (chlorine, bromine, iodine) have 7 outer electrons and react by gaining one electron to form ions. They become less reactive down the group, because the outer shell is further from the nucleus, so an electron is gained less easily. A more reactive halogen will displace a less reactive one from its compound (for example chlorine displaces bromine).
Group 0: the noble gases
The noble gases (helium, neon, argon) have full outer shells, which is a very stable arrangement. Because they do not need to gain, lose or share electrons, they are unreactive (inert). This is why they are used where an unreactive gas is needed, such as argon in light bulbs.
Reactions of the alkali metals with water
A classic Group 1 reaction is with water. An alkali metal reacts with water to give hydrogen gas and a metal hydroxide (an alkali), for example: sodium + water to sodium hydroxide + hydrogen. The reaction gets more vigorous down the group: lithium fizzes gently, sodium melts into a ball and whizzes about, and potassium reacts so fast it ignites the hydrogen with a lilac flame. This is direct evidence of the increasing reactivity down Group 1, and a common exam description.
Metals and non-metals
The Periodic Table is split into metals (the majority, on the left and centre) and non-metals (on the right). Metals are typically shiny, good conductors of heat and electricity, malleable, and form positive ions by losing electrons. Non-metals are typically dull, poor conductors (except graphite), brittle as solids, and form negative ions by gaining electrons or share electrons. Knowing the metal and non-metal regions helps you predict how an element behaves and what kind of bonding it forms.
Try this
Q1. State what the elements in a group have in common about their electrons. [1 mark]
- Cue. They have the same number of electrons in their outer shell.
Q2. Why are the Group 0 noble gases unreactive? [1 mark]
- Cue. They have full outer electron shells, a stable arrangement.
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC style4 marksExplain why reactivity increases down Group 1 but decreases down Group 7.Show worked answer →
A Unit 2 explain question worth 4 marks. Reward: Group 1 metals react by losing their one outer electron; going down the group the outer electron is further from the nucleus and more shielded, so it is lost more easily, making the metal more reactive (2). Group 7 non-metals react by gaining an electron; going down the group the outer shell is further from the nucleus, so an electron is gained less easily, making them less reactive (2). Markers credit the electron change and the distance/shielding for each group. A common error is to give the same trend for both.
WJEC style3 marksChlorine is added to potassium bromide solution. Describe what happens and write the word equation.Show worked answer →
A Unit 2 displacement question. Reward: chlorine is more reactive than bromine, so it displaces the bromine (1); the solution changes colour as bromine is formed (1); the word equation is chlorine + potassium bromide to potassium chloride + bromine (1). Markers credit the displacement, the observation and the equation. A common error is to say bromine displaces chlorine.
Related dot points
- How electrons fill shells, the electronic structures of the first twenty elements, and linking outer electrons to group and shells to period.
A focused answer to the WJEC GCSE Science Double Award Unit 2 topic on electronic structure, covering how electrons fill shells, the electronic structures of the first twenty elements, and how the structure links to an element's group and period.
- Sub-atomic particles and their relative masses and charges, working out particle numbers from atomic and mass number, isotopes, and calculating relative atomic mass.
A focused answer to the WJEC GCSE Science Double Award Unit 2 topic on atoms, covering protons, neutrons and electrons and their relative masses and charges, atomic and mass number, particles in atoms and ions, isotopes, and calculating relative atomic mass.
- Ionic bonding as the transfer of electrons between metals and non-metals, the formation of ions, and the properties of ionic compounds.
A focused answer to the WJEC GCSE Science Double Award Unit 5 topic on ionic bonding, covering how electrons are transferred between metals and non-metals to form ions, the giant ionic lattice, and the properties of ionic compounds.