How is the Periodic Table organised, and what are the trends in Groups 1, 7 and 0?
Describe the arrangement of the Periodic Table, distinguish metals and non-metals, and explain trends in Group 1, Group 7 and Group 0.
A focused answer to WJEC GCSE Chemistry topic 1.2, covering how the Periodic Table is arranged by atomic number, the difference between metals and non-metals, and the properties and trends of the alkali metals (Group 1), halogens (Group 7) and noble gases (Group 0).
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What this topic is asking
WJEC topic 1.2 wants you to describe how the Periodic Table is arranged, tell metals from non-metals, and explain the trends and reactions of three key groups: Group 1 (the alkali metals), Group 7 (the halogens) and Group 0 (the noble gases).
How the Periodic Table is arranged
Because elements in the same group share the same number of outer electrons, they react in similar ways. This is the central idea that makes the table so useful for predicting properties.
Metals and non-metals
Most elements are metals, found on the left and centre of the table. Non-metals are on the right. Their typical properties are:
- Metals: shiny, good conductors of heat and electricity, malleable (can be hammered into shape) and usually have high melting points. They tend to lose electrons to form positive ions.
- Non-metals: often dull, poor conductors (except graphite), brittle when solid and have lower melting points. They tend to gain or share electrons.
Group 1: the alkali metals
The alkali metals (lithium, sodium, potassium) all have one outer electron. They are soft, low-density metals that react with water to give hydrogen gas and an alkaline hydroxide solution, for example:
They also react with oxygen to form oxides and with chlorine to form chlorides (white salts).
Group 7: the halogens
The halogens (chlorine, bromine, iodine) all have seven outer electrons. They exist as diatomic molecules (, , ). Down the group they get darker and change state from gas (chlorine) to liquid (bromine) to solid (iodine).
For example, chlorine displaces bromine: .
Group 0: the noble gases
The noble gases (helium, neon, argon) have full outer shells (helium has 2, the rest have 8). A full outer shell is very stable, so the noble gases are unreactive (inert) and exist as single atoms. This is why they are used where an unreactive atmosphere is needed, such as argon in light bulbs and helium in balloons.
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 sample4 marksDescribe what happens when sodium is added to water, and explain how the reactivity of the Group 1 metals changes down the group.Show worked answer β
A Unit 1.2 structured question. Reward: sodium floats on the water, melts into a ball, fizzes and moves around the surface, giving off hydrogen gas and forming sodium hydroxide (an alkaline solution). The reactivity of the Group 1 metals increases down the group. This is because the outer electron is in a shell further from the nucleus and is more shielded, so it is lost more easily, making reactions faster and more vigorous. Markers credit a description of the observations and the explanation linking increasing reactivity to the outer electron being lost more easily down the group. A common error is to reverse the trend.
WJEC sample3 marksExplain why chlorine can displace bromine from potassium bromide solution, but bromine cannot displace chlorine from potassium chloride.Show worked answer β
A Unit 1.2 displacement question. Reward: chlorine is more reactive than bromine because it is higher up Group 7. A more reactive halogen displaces a less reactive halogen from a solution of its salt, so chlorine displaces bromine: . Bromine is less reactive than chlorine, so it cannot displace chlorine. Markers credit the reactivity order (chlorine more reactive than bromine), the rule that a more reactive halogen displaces a less reactive one, and the correct direction. A common slip is to get the reactivity trend down Group 7 the wrong way round.
Related dot points
- Describe the arrangement of electrons into shells for the first twenty elements and relate electronic structure to group and period in the Periodic Table.
A focused answer to WJEC GCSE Chemistry topic 1.2, covering how electrons fill shells, writing the electronic structures of the first twenty elements, and relating the number of outer electrons to group number and the number of shells to period number.
- Describe sub-atomic particles and their relative masses and charges, work out particle numbers from atomic and mass number, define isotopes, and calculate relative atomic mass.
A focused answer to WJEC GCSE Chemistry topic 1.2, covering protons, neutrons and electrons and their relative masses and charges, atomic number and mass number, working out particle numbers for atoms and ions, isotopes, and calculating relative atomic mass.
- Distinguish between elements, compounds and mixtures, interpret chemical formulae, and tell physical changes apart from chemical reactions.
A focused answer to WJEC GCSE Chemistry topic 1.1, covering the difference between elements, compounds and mixtures, reading chemical formulae, and distinguishing physical changes from chemical reactions with evidence such as colour change and gas production.
- Describe ionic bonding as electron transfer, draw dot-and-cross diagrams for simple ionic compounds, and relate the giant ionic lattice to the properties of ionic compounds.
A focused answer to WJEC GCSE Chemistry topic 2.1, covering ionic bonding as the transfer of electrons between metals and non-metals, drawing dot-and-cross diagrams, the giant ionic lattice, and how the structure explains high melting points and conduction when molten or dissolved.
Sources & how we know this
- WJEC GCSE Chemistry specification (from 2016) β WJEC (2016)