Group 1 — AQA GCSE Chemistry
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Group 1 explained
Group 1 covers 4 specification points, including The elements in Group 1 of the periodic table… and Students should be able to describe the….
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The elements in Group 1 of the periodic table are known as the alkali metals and have characteristic properties because of the single electron in their outer shell.
Group 1 contains lithium, sodium, potassium, rubidium, caesium and francium. Each atom has one electron in its outer shell, so it can lose that electron to form a 1⁺ ion with a stable full outer shell. This single outer electron explains the characteristic properties: they are soft, low density, shiny when freshly cut but tarnish quickly, and they react vigorously with water, oxygen and chlorine. Because only one electron must be lost, the metals are highly reactive and form ionic compounds in which the metal ion has a 1⁺ charge. Their reactivity and physical properties are therefore directly linked to their electronic structure.
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 lithium oxide, Li₂O, sodium oxide, Na₂O, and potassium oxide, K₂O; sodium and potassium may also form peroxides or superoxides, but the oxide is the expected product at this level. With chlorine, they burn to form white metal chlorides such as lithium chloride, LiCl, sodium chloride, NaCl, and potassium chloride, KCl. With water, they produce a metal hydroxide and hydrogen gas, for example 2Na + 2H₂O → 2NaOH + H₂. Reactivity increases from lithium to sodium to potassium, so potassium reacts most vigorously, often igniting the hydrogen produced.
In Group 1, the reactivity of the elements increases going down the group.
Going down Group 1 from lithium to sodium to potassium, the atoms have more electron shells, so the outer electron is further from the nucleus and is shielded by more inner shells. The attraction between the nucleus and the outer electron is therefore weaker, so the electron is lost more easily. This makes the metals more reactive down the group: lithium reacts steadily with water, sodium reacts vigorously and may melt, and potassium reacts so vigorously that the hydrogen produced often ignites with a lilac flame. The trend can be used to predict that rubidium and caesium would react even more vigorously, sometimes explosively.
Students should be able to: explain how properties of the elements in Group 1 depend on the outer shell of electrons of the atoms predict properties from given trends down the group. AQA GCSE Chemistry 8462. GCSE exams Jun
Group 1 metals, the alkali metals, each have one electron in their outer shell. That single outer electron is lost relatively easily when the metal reacts, forming a 1⁺ ion and giving the group its characteristic reactivity. Down the group, atomic radius increases and the outer electron is further from the nucleus and shielded by more inner shells, so the attraction holding it is weaker. Consequently reactivity increases down Group 1: lithium reacts steadily, sodium more vigorously, potassium vigorously enough to ignite, and rubidium and caesium are more reactive still. Melting points and boiling points decrease down the group because metallic bonding weakens as ions become larger and charge density falls. To predict properties, identify the trend from the data given, then extend it to the next element, justifying the prediction using outer-shell electron loss and increased atomic size.
Your focus
- Identify the single outer electron in a Group 1 atom and state the ion it forms.
- Relate the electronic structure of alkali metals to their characteristic physical and chemical properties.
- Write the formula and charge of a Group 1 ion using correct notation.
Show all 12 objectives
- Write word and balanced symbol equations for the reactions of lithium, sodium and potassium with oxygen, chlorine and water.
- Describe the observations seen when each alkali metal reacts with water.
- Compare the vigour of the reactions of lithium, sodium and potassium.
- Describe the trend in reactivity of Group 1 metals down the group.
- Explain the trend in terms of atomic radius, shielding and ease of losing the outer electron.
- Predict the reactivity of a named Group 1 metal below potassium.
- Describe the outer-shell 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 down Group 1.
- Use given trend data to predict a property of a Group 1 element and justify the prediction.
Group 1 exam tips
Marking Points
- States that Group 1 atoms each have one electron in their outer shell.
- Explains that losing this single outer electron forms a 1⁺ ion with a full outer shell.
- Links the single outer electron to the characteristic reactivity of the alkali metals.
- Describes typical physical properties such as softness, low density and shiny appearance when freshly cut.
- Recalls that alkali metals form ionic compounds in which the metal ion carries a 1⁺ charge.
- Identifies that the vigorous reactions with water, oxygen and chlorine are characteristic of the single outer electron being lost.
- Names the first three alkali metals as lithium, sodium and potassium.
- Describes the reaction with oxygen to form a metal oxide, giving a correct example such as 4Na + O₂ → 2Na₂O.
- Describes the reaction with chlorine to form a white metal chloride, giving a correct example such as 2Na + Cl₂ → 2NaCl.
- Describes the reaction with water to form a metal hydroxide and hydrogen, giving a correct example such as 2K + 2H₂O → 2KOH + H₂.
- States that reactivity increases from lithium to sodium to potassium, so potassium reacts most vigorously.
- Describes observations such as fizzing, movement on the water surface and the metal becoming smaller.
- States that reactivity increases from lithium to sodium to potassium and continues down the group.
- Explains that atoms lower in Group 1 have more electron shells and a larger atomic radius.
- Explains that the outer electron is further from the nucleus and more shielded, so it is lost more easily.
- Links easier loss of the outer electron to increased reactivity down the group.
- Uses the trend to predict that rubidium and caesium react more vigorously than potassium.
- Describes the increasing vigour of reactions with water from lithium to potassium.
- State that Group 1 atoms each have one electron in their outer shell and lose it to form a 1⁺ ion.
- Explain that down the group the outer electron is in a shell further from the nucleus and is shielded by more inner shells, so less energy is needed to remove it.
- Link weaker attraction for the outer electron to increased reactivity down the group.
- Use given data, such as melting point or reaction observations, to identify a trend and predict a property of another Group 1 element.
- Justify a prediction by referring to atomic size, shielding and the ease of losing the outer electron.
- Describe observations such as fizzing, movement on water and flame colour as evidence of reactivity.
Examiner Tips
- 💡Always link the single outer electron to both the 1⁺ ion formed and the high reactivity.
- 💡When describing physical properties, give at least two observable features such as softness and low density.
- 💡Use the correct superscript notation for ions, for example K⁺, in all written answers.
- 💡Learn the general word equations for oxygen, chlorine and water before learning specific balanced equations.
- 💡When describing observations, include fizzing, floating, movement and the metal shrinking or disappearing.
- 💡Check balancing by counting atoms of each element on both sides of the equation.
- 💡Always link the trend to the distance and shielding of the outer electron, not just to atomic size.
- 💡Use comparative phrases such as more easily lost and more vigorously when explaining the trend.
- 💡When predicting, name the element and state whether it reacts more or less vigorously than potassium.
- 💡When asked to predict, quote the trend in the data first, then state the predicted value or behaviour for the named element.
- 💡Use the phrase outer electron throughout your explanation, because it keeps the answer focused on electronic structure.
- 💡For six-mark questions, structure your answer as electronic structure, then distance and shielding, then reactivity, then a prediction.
- 💡Check that any ion you write uses a superscript charge, for example Li⁺, not a baseline form.
Common Mistakes
- Saying Group 1 atoms gain one electron to fill their outer shell; correct this by stating they lose one electron to form a 1⁺ ion.
- Writing the ion charge as a postfix number; correct this by using the superscript form, for example Na⁺.
- Describing alkali metals as hard and dense; correct this by stating they are soft and have low density.
- Writing hydrogen as the only product of the reaction with water; correct this by including the metal hydroxide as well.
- Balancing equations incorrectly, for example leaving oxygen atoms unequal; correct this by checking that each element has the same number of atoms on both sides.
- Stating that lithium reacts more vigorously than potassium; correct this by ordering reactivity as lithium < sodium < potassium.
- Saying reactivity decreases down Group 1 because atoms get bigger; correct this by explaining that the outer electron is lost more easily, so reactivity increases.
- Confusing shielding with a stronger nuclear attraction; correct this by stating that more inner shells reduce the attraction felt by the outer electron.
- Assuming all Group 1 metals react identically with water; correct this by describing the increasing vigour from lithium to potassium.
- Saying reactivity decreases down Group 1 because atoms get bigger; correct this by explaining that the larger distance and extra shielding weaken the attraction for the outer electron, so reactivity increases.
- Confusing Group 1 with Group 7 trends; correct this by stating that Group 1 reactivity increases down the group whereas Group 7 reactivity decreases.
- Writing the ion as a baseline numeral with a postfix sign; correct this by using the superscript form such as Na⁺ and K⁺.
- Treating melting point and reactivity as following the same trend; correct this by noting that melting point decreases down Group 1 while reactivity increases.