Group 1 — AQA GCSE Combined Science
Test yourself on Group 1 with AQA GCSE practice questions.
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Group 1 explained
Group 1 sits on the far left of the periodic table and contains lithium, sodium, potassium, rubidium, caesium and francium.
Read the full explanation
Each atom has one electron in its outer shell, so losing that electron gives a stable noble-gas arrangement and a 1⁺ ion. This single outer electron explains the characteristic properties: low density (atoms are large with loosely held outer electrons), softness (metallic bonding is weak because each atom contributes only one delocalised electron), low melting points that decrease down the group, and high reactivity that increases down the group as the outer electron is further from the nucleus and shielded by more inner shells. They are called alkali metals because they react with water to form alkaline metal hydroxide solutions, for example 2Na + 2H₂O → 2NaOH + H₂.
Students should be able to describe the reactions of the first three alkali metals with oxygen, chlorine and water.
The first three alkali metals are lithium, sodium and potassium. With oxygen they burn in air to form metal oxides, for example 4Li + O₂ → 2Li₂O, and the reaction becomes more vigorous down the group. With chlorine they react when heated to form white metal chlorides, for example 2Na + Cl₂ → 2NaCl. With water they produce a metal hydroxide and hydrogen, for example 2K + 2H₂O → 2KOH + H₂; lithium fizzes steadily, sodium moves rapidly and may melt, and potassium reacts so vigorously that the hydrogen ignites with a lilac flame. Observations such as fizzing, movement, melting and flame colour show the increasing reactivity from lithium to potassium.
In Group 1, the reactivity of the elements increases going down the group.
Group 1 metals, the alkali metals, each have one electron in their outer shell. Going down the group from lithium to sodium to potassium, the atoms gain extra inner shells, so the outer electron is further from the nucleus and is shielded by more inner electrons. The force of attraction between the nucleus and the outer electron therefore weakens, so the outer electron is lost more easily. Reactivity is judged by how readily the metal loses that outer electron to form a 1⁺ ion, so reactivity increases down the group. For example, lithium fizzes steadily in water, sodium reacts more vigorously and may melt, and potassium reacts so vigorously that the hydrogen produced ignites with a lilac flame.
explain how properties of the elements in Group 1 depend on the outer shell of electrons of the atoms
Group 1 elements (lithium, sodium, potassium, rubidium, caesium) each have one electron in their outer shell, and this single outer electron controls their properties. Atoms lose this electron to form 1⁺ ions, giving a stable noble-gas electron arrangement. The ease of losing it increases down the group because the outer electron is further from the nucleus and shielded by more inner shells, so the attraction is weaker. This explains why reactivity increases down Group 1: lithium reacts slowly with water, sodium vigorously, potassium violently. It also explains the pattern in melting points, which decrease down the group as atomic radius increases and metallic bonding weakens. The single outer electron therefore links electron configuration to observed chemical and physical behaviour.
predict properties from given trends down the group.
When you are given data or a described trend for Group 1, you can predict properties of an element lower down the group. For example, if reactivity increases from lithium to sodium to potassium, you can predict that rubidium and caesium react even more vigorously with water. Similarly, if melting points decrease down the group, you can predict that rubidium has a lower melting point than potassium. To make a valid prediction, identify the direction of the trend, check the pattern is consistent, then state the property for the named element and justify it using the outer electron. Predictions should be consistent with the trend and explained using atomic structure, not guessed.
Your focus
- State that Group 1 elements have one electron in their outer shell and form 1⁺ ions.
- Explain how the single outer electron causes the characteristic physical and chemical properties of alkali metals.
- Describe and explain the trend in reactivity down Group 1 using atomic radius and shielding.
Show all 15 objectives
- Describe the reactions of lithium, sodium and potassium with oxygen, chlorine and water.
- Write word and balanced symbol equations for these reactions.
- Compare the vigour of the reactions of lithium, sodium and potassium and relate this to the trend in reactivity.
- Describe the trend in reactivity of Group 1 metals down the group.
- Explain the trend in terms of distance from the nucleus and shielding of the outer electron.
- Relate the trend to observations of Group 1 metals reacting with water.
- Describe the electron configuration of Group 1 atoms and the ion they form.
- Explain how distance from the nucleus and shielding affect the loss of the outer electron.
- Relate the outer electron to trends in reactivity and melting point down Group 1.
- Identify the direction of a trend from given data or information.
- Predict a property for a named Group 1 element using the trend.
- Justify a prediction by referring to the outer electron and atomic structure.
Group 1 exam tips
Marking Points
- Group 1 elements each have one electron in their outer shell and lose it to form a 1⁺ ion with a stable noble-gas electron arrangement.
- Reactivity increases down Group 1 because the outer electron is further from the nucleus and shielded by more inner shells, so less energy is needed to remove it.
- Physical properties include low density, softness and relatively low melting points, all linked to weak metallic bonding with only one delocalised electron per atom.
- Alkali metals react with water to form a metal hydroxide and hydrogen, giving an alkaline solution, which is why they are called alkali metals.
- Trends down the group include decreasing melting point and increasing reactivity, which can be explained by increasing atomic radius and shielding.
- Lithium, sodium and potassium all react with oxygen to form metal oxides, and the reactions become more vigorous down the group.
- The alkali metals react with chlorine to form white metal chlorides, for example sodium chloride, when heated.
- Reactions with water produce a metal hydroxide and hydrogen gas, and the hydroxide makes the solution alkaline.
- Observations for water reactions include fizzing, the metal moving on the surface, melting into a ball and, for potassium, a lilac flame.
- Word and balanced symbol equations can be written for each reaction, for example 2Li + 2H₂O → 2LiOH + H₂.
- State that Group 1 elements have one electron in their outer shell and form 1⁺ ions by losing it.
- Explain that going down the group the outer electron is in a shell further from the nucleus.
- Explain that increased shielding by inner shells and greater distance reduce the attraction between the nucleus and the outer electron.
- Conclude that the outer electron is lost more easily down the group, so reactivity increases.
- Support the trend with a comparison of reactions with water, such as lithium fizzing gently while potassium ignites.
- Group 1 atoms have one electron in their outer shell, so they lose one electron to form a 1⁺ ion with a stable noble-gas configuration.
- The outer electron is held less strongly down the group because it is further from the nucleus and shielded by additional inner shells.
- Reactivity increases down the group because the outer electron is lost more easily, so reactions with water become more vigorous.
- Melting points decrease down the group because atomic radius increases and the metallic bond weakens as the outer electron is further from the positive nucleus.
- The single outer electron explains why Group 1 elements form ionic compounds with a 1⁺ charge and show similar chemical reactions.
- Identify the direction of the trend from the given data, such as reactivity increasing or melting point decreasing down Group 1.
- State a predicted property for a named element, for example 'rubidium reacts more vigorously with water than potassium'.
- Justify the prediction using atomic structure: the outer electron is further from the nucleus and more shielded, so it is lost more easily.
- Check that the prediction follows the same pattern as the given trend and does not contradict the data.
- Use the trend to compare two elements, such as predicting that caesium has a lower melting point than rubidium.
Examiner Tips
- 💡Link every property you describe back to the single outer electron, because the question asks for the cause, not just the property.
- 💡Use the correct trend direction: reactivity increases down the group, while melting point and density trends should be stated carefully.
- 💡When giving an equation, balance it and include state symbols if asked, for example 2K + 2H₂O → 2KOH + H₂.
- 💡Name the metal, the reactant and the products clearly, and include the correct formulae for oxides, chlorides and hydroxides.
- 💡Use comparative language such as more vigorous or less vigorous to show the trend from lithium to potassium.
- 💡When describing observations, link them to the reaction, for example fizzing shows hydrogen gas being produced.
- 💡Link each step of the explanation to the structure of the atom: outer shell, distance and shielding.
- 💡Use the phrase 'outer electron is lost more easily' rather than vague wording such as 'more reactive'.
- 💡When asked to compare, name two specific metals and describe the difference in their reactions with water.
- 💡Link each property to the outer electron explicitly, for example 'reactivity increases because the outer electron is lost more easily'.
- 💡Use comparative language such as 'further from the nucleus' and 'more shielding' rather than just 'bigger atom'.
- 💡When describing trends, name the elements or give a specific reaction, such as potassium reacting more vigorously than lithium with water.
- 💡Underline the trend in the question before predicting, so your answer follows the given direction.
- 💡Name the element you are predicting for and compare it with a known element from the trend.
- 💡Add a short justification using the outer electron to move from a simple prediction to a full explanation.
Common Mistakes
- Saying Group 1 elements have one electron in total rather than one electron in their outer shell; correct this by stating the outer-shell configuration, for example sodium is 2,8,1.
- Claiming reactivity decreases down Group 1; correct this by explaining that the outer electron is lost more easily as atomic radius and shielding increase.
- Writing that alkali metals form 2⁺ ions; correct this by linking the single outer electron to a 1⁺ charge, as in Na⁺ and K⁺.
- Writing that alkali metals react with water to produce an acid; correct this by stating that a metal hydroxide is formed, giving an alkaline solution.
- Forgetting that hydrogen gas is produced with the hydroxide; correct this by including H₂ in the products and balancing the equation.
- Describing potassium as reacting less vigorously than lithium; correct this by stating that reactivity increases down the group, so potassium is the most vigorous of the three.
- Saying reactivity decreases down Group 1 because atoms get bigger; correction: bigger atoms lose the outer electron more easily, so reactivity increases.
- Confusing Group 1 with Group 7, where reactivity decreases down the group; correction: the two trends run in opposite directions.
- Claiming the outer electron is pulled away by water; correction: the electron is lost because the attraction from the nucleus is weaker, and water is the reactant that accepts it in the reaction.
- Saying Group 1 atoms gain an electron to fill the outer shell; correct this by stating they lose one electron to form a 1⁺ ion.
- Claiming reactivity decreases down the group; correct this by linking increased distance and shielding to easier electron loss and greater reactivity.
- Writing the ion as Na⁺ but then describing it as a 1⁻ ion; correct this by keeping the charge consistent as 1⁺ throughout.
- Predicting a value that reverses the trend, such as saying rubidium is less reactive than potassium; correct this by checking the direction of the trend first.
- Giving a prediction without a reason; correct this by adding a structural explanation about the outer electron.
- Assuming all properties follow the same direction; correct this by treating each property separately, since reactivity increases but melting point decreases down Group 1.