Group I - Alkali metals
Cambridge IGCSE Chemistry (0620) · Unit 8: The Periodic Table · 14 flashcards
Group I - Alkali metals is topic 8.2 in the Cambridge IGCSE Chemistry (0620) syllabus , positioned in Unit 8 — The Periodic Table , alongside Arrangement of elements, Group VII - Halogens and Group VIII - Noble gases.
This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical). Past papers from 2022 to 2025 show this topic across undefined questions worth 377 marks (around 6.0% of all Chemistry marks in those years).
The deck below contains 14 flashcards — 11 key concepts, 2 identification cards and 1 study tip — covering the precise wording mark schemes reward.
Watch out: one common mark-loser flagged on this topic — read the study-tip card below before attempting past-paper questions.
What the Cambridge 0620 syllabus says
Official 2026-2028 specThese are the exact learning objectives Cambridge sets for this topic. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks.
- Describe Describe the Group I alkali metals, lithium, sodium and potassium, as relatively soft metals with general trends down the group, limited to: (a) decreasing melting point (b) increasing density (c) increasing reactivity
- Predict Predict the properties of other elements in Group I, given information about the elements
Common mark-losers in Group I - Alkali metals
Describe the safety precautions needed when handling Group I metals.
Group I metals are stored under oil because they react vigorously with air (oxygen) and water.
Precautions:
• Use small pieces only
• Handle with forceps, never bare hands (they react with moisture on skin)
• Cut with a knife on a tile — the freshly cut surface tarnishes quickly in air
• Keep away from water — the reaction produces flammable hydrogen gas
• Potassium and below are especially dangerous as they can ignite or explode
Describe the general trend in melting point as you descend Group I (alkali metals).
The melting point decreases as you go down Group I.
Describe the general trend in density as you descend Group I (alkali metals).
The density increases as you go down Group I.
Describe the general trend in reactivity as you descend Group I (alkali metals).
The reactivity increases as you go down Group I. This means Potassium reacts more vigorously than Sodium with water, and Sodium more vigorously than Lithium.
Explain how metallic bonding holds Group I metals together.
Metallic bonding involves positive ions/atoms in a sea of delocalized electrons. There's an attraction between the positive ions and these mobile electrons. Electrons move/are mobile/flow.
Predict the colour of the flame produced when Sodium is heated in a flame test.
Sodium produces a yellow to orange flame in a flame test. This is a characteristic property used to identify sodium ions.
Describe a property of Group I elements that makes them less suitable for structural purposes than transition metals.
Group I elements are less strong / not strong, have low(er) density and are soft(er) compared to transition metals, making them less suitable for structural purposes.
What is the general formula of the hydroxide formed when a Group I element reacts with water?
The general formula is XOH, where X represents the Group I element.
Order the following Group I elements in terms of increasing reactivity: Lithium, Sodium, Potassium, Rubidium, Caesium.
The order of increasing reactivity is: Lithium → Sodium → Potassium → Rubidium → Caesium. Caesium is the most reactive.
If a Group I element reacts with bromine, which species loses electron(s)?
When a Group I element reacts with bromine, the Group I element loses its valence electron to form a positive ion. Bromine gains this electron to form a bromide ion.
Describe the trends in Group I as you go down the group.
As you go down Group I (Li → Na → K → Rb → Cs):
• Reactivity increases — the outer electron is further from the nucleus and easier to lose
• Melting point decreases — metallic bonding gets weaker as atomic radius increases
• Density generally increases (except Li < Na)
• Softness increases — metals become easier to cut
• Atomic radius increases — more electron shells
Predict the properties of rubidium (Rb) based on the trends in Group I.
Rubidium is below potassium in Group I, so we predict:
• More reactive than potassium with water — likely to explode on contact
• Softer than potassium — very easy to cut with a knife
• Lower melting point than potassium (K = 63°C, so Rb will be lower, ~39°C)
• Higher density than potassium
• Forms Rb₂O (rubidium oxide) and RbOH (rubidium hydroxide)
• One electron in outer shell, forming Rb⁺ ions
Why does reactivity increase going down Group I?
Going down Group I, each element has one more electron shell. The outer electron is further from the nucleus and experiences greater shielding from inner electrons. This means the attraction between the nucleus and the outer electron is weaker, so the outer electron is lost more easily. Since Group I metals react by losing their outer electron, they become more reactive down the group.
What compounds do Group I metals form and what are their properties?
Group I metals form:
• Oxides (
Describe the safety precautions needed when handling Group I metals.
Group I metals are stored under oil because they react vigorously with air (oxygen) and water.
Precautions:
• Use small pieces only
• Handle with forceps, never bare hands (they react with moisture on skin)
• Cut with a knife on a tile — the freshly cut surface tarnishes quickly in air
• Keep away from water — the reaction produces flammable hydrogen gas
• Potassium and below are especially dangerous as they can ignite or explode
Tips to avoid common mistakes in Group I - Alkali metals
- ● Metals BELOW carbon in the reactivity series can be extracted from their oxides using carbon; metals ABOVE carbon need electrolysis.
- ● Consider both what a metal does and does not react with to gauge its reactivity.
- ● Learn common applications: aluminium is used where lightness and corrosion resistance are key, stainless steel for its strength and resistance to rust.
- ● Create a table summarizing the reactions of common metals (Ca, Mg, Zn, Fe, Cu) with water, steam, and dilute acids, linking it to the metal reactivity series.
- ● Relate metal extraction method to reactivity: electrolysis (most reactive), carbon reduction (intermediate), native state (least reactive).
More topics in Unit 8 — The Periodic Table
Group I - Alkali metals sits alongside these Chemistry decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 0620 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Related Chemistry guides
Long-read articles that go beyond the deck — cover the whole subject's common mistakes, high-yield content and revision pacing.
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