Introduction to Group 1 Elements - The Alkali Metals Revision Notes | GCSE AQA Higher Chemistry
Alkali metals are soft enough to cut with a knife, have low melting points and low density. Free GCSE AQA notes with key terms and 12 questions answered.
Updated 19 Mar 2026 · Revise Right Team
Introduction to Group 1 Elements - The Alkali Metals is part of The periodic table in GCSE AQA Higher Chemistry.
4 min
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What this lesson covers
Alkali metals are soft enough to cut with a knife, have low melting points and low density. Free GCSE AQA notes with key terms and 12 questions answered.
Explain why Group 1 elements are called alkali metals and describe their characteristic properties
Describe how the properties of Group 1 elements change as you go down the group
Explain how the single outer electron determines the properties of alkali metals
Predict the products of reactions between alkali metals and water
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Use this lesson to stay inside The periodic table while connecting the detail back to the wider Topic 1: Atomic structure and the periodic table topic.
Topic 1: Atomic structure and the periodic table
The periodic table
GCSE AQA Higher Chemistry
Revision notes
Read the core explanations from Introduction to Group 1 Elements - The Alkali Metals before testing yourself from memory.
1. Meet the Alkali Metals - The Most Reactive Group
Why do sodium and potassium explode when they touch water, but iron just rusts slowly? The answer lies in a special group of elements called the alkali metals.
Group 1 elements - lithium, sodium, potassium, rubidium, caesium, and francium - are known as the alkali metals. They're called this because they all react with water to form alkaline solutions (pH above 7). What makes them so special is that they all have exactly one electron in their outer shell.
This single outer electron is the key to understanding everything about these metals - their reactivity, their properties, and why they behave so differently from other elements. Let's see how this works.
2. The Single Electron - Why It Changes Everything
Picture an atom like a layered onion. The nucleus sits in the centre, surrounded by shells of electrons. Group 1 elements have their outer shell containing just one lonely electron, while the inner shells are completely full.
This single outer electron is weakly attracted to the nucleus because it's far away and shielded by all the inner electrons. It's like trying to hear someone whisper from across a crowded room - the signal is weak. This makes the electron easy to remove.
When alkali metals react, they lose this outer electron to form positive ions with a 1+ charge. For example, sodium becomes Na⁺ and potassium becomes K⁺. This is why all Group 1 elements form ionic compounds with the same charge pattern.
3. The Reactivity Trend - Why Size Matters
Here's where it gets interesting. As you go down Group 1, the elements become more reactive. Lithium fizzes gently in water, sodium dances around on the surface, and potassium actually catches fire. Why does this happen?
The answer is atomic size. As you go down the group, the atoms get bigger because they have more electron shells. The outer electron gets further and further from the nucleus, making it even easier to remove.
Worked example: Understanding the Reactivity Trend
Explain why potassium is more reactive than lithium, using atomic structure.
Li: 2,1 electron arrangement
K: 2,8,8,1 electron arrangement — Both have 1 outer electron, but potassium has more shells
Potassium atom is much larger than lithium atom — More electron shells means bigger atomic radius
K outer electron is further from nucleus than Li outer electron — Distance weakens the electrostatic attraction
K has more inner electron shells shielding the outer electron — More shielding = weaker attraction to nucleus
Answer: Potassium is more reactive because its outer electron is further from the nucleus and more shielded, so it's easier to remove
This trend continues down the group. Rubidium and caesium are even more reactive than potassium, though you won't see them in school labs because they're too dangerous to handle safely.
4. Characteristic Properties of Alkali Metals
Because all Group 1 elements have the same outer electron arrangement, they share similar properties. Here are the key characteristics you need to know for your exams.
Physical Properties: All alkali metals are soft (you can cut them with a knife), have low melting points compared to other metals, and have low density. Lithium, sodium, and potassium actually float on water because they're less dense than water.
Chemical Properties: They all react vigorously with water to produce hydrogen gas and an alkaline solution. The general equation is: Metal + Water → Metal hydroxide + Hydrogen
They also react with oxygen to form metal oxides, and with halogens to form ionic compounds called salts. For example, sodium + chlorine → sodium chloride (table salt).
5. Observing the Reactions - What You'll See in Practicals
In your GCSE practicals, you'll likely observe lithium, sodium, and potassium reacting with water. Here's what to look for and how to explain your observations.
Worked example: Required Practical: Observing Group 1 Reactions
Describe and explain the observations when lithium, sodium, and potassium react with water.
Fizzes gently, moves slowly across water surface, dissolves — Least reactive - hydrogen gas produced slowly
Fizzes vigorously, moves quickly, forms a ball, may catch fire — More reactive - more hydrogen produced, heat generated
Fizzes violently, catches fire immediately, purple flame, very fast movement — Most reactive - lots of heat ignites hydrogen gas
Universal indicator turns blue/purple (pH 12-14) — Metal hydroxide formed makes solution alkaline
Answer: Reactivity increases down the group due to easier loss of outer electron
6. Exam Technique - Getting Full Marks on Group 1 Questions
Group 1 questions often test your understanding of trends and your ability to explain observations. Here's how to tackle the most common question types.
Common Exam Mistakes: Don't say alkali metals 'want' to lose electrons - they lose them because the outer electron is weakly held. Don't confuse Group 1 (alkali metals) with Group 2 (alkaline earth metals). Always balance chemical equations - check your atom count on both sides.
Sources and content standards
Published by Revise Right. Use the official specification reference to check the requirements for your course. Content updated: 2026-03-19.
Alkali metals are soft enough to cut with a knife, have low melting points compared to other metals and have low density; lithium, sodium and potassium float on water. They react vigorously with water to produce hydrogen and an alkaline solution, and react with oxygen and halogens.
What happens when potassium reacts with water?
When potassium reacts with water, it fizzes violently, catches fire immediately with a purple flame and moves very fast. It is the most reactive of the three, and the heat produced ignites the hydrogen gas.
What happens when lithium reacts with water?
When lithium reacts with water, it fizzes gently, moves slowly across the water surface and dissolves. Lithium is the least reactive of lithium, sodium and potassium, so hydrogen is produced slowly.
Why does reactivity increase down Group 1?
Reactivity increases down Group 1 because the atoms get bigger, with more electron shells, so the single outer electron is further from the nucleus and more shielded by inner electrons. The attraction to the nucleus is weaker, so the outer electron is easier to remove; potassium (2,8,8,1) is more reactive than lithium (2,1).
What do alkali metals form with halogens?
Alkali metals react with halogens to form ionic compounds called salts, for example sodium + chlorine → sodium chloride (table salt). They also react with oxygen to form metal oxides.
Why are Group 1 elements called alkali metals?
Group 1 elements are called alkali metals because they all react with water to form alkaline solutions, with a pH of more than 7. They are lithium, sodium, potassium, rubidium, caesium and francium, and they all have exactly one electron in their outer shell.
What happens when alkali metals react with water?
Alkali metals react with water to form a metal hydroxide and hydrogen. Lithium fizzes gently and moves slowly, sodium fizzes vigorously and forms a ball, and potassium fizzes violently and catches fire immediately; universal indicator turns blue/purple (pH 12-14).
Why do Group 1 metals form 1+ ions?
Group 1 metals form ions with a 1+ charge because they lose their single outer electron when they react, such as sodium forming Na⁺ and potassium forming K⁺. The outer electron is weakly held because it is far from the nucleus and shielded by inner electrons.
What is the word equation for an alkali metal and water?
The word equation for an alkali metal and water is metal + water → metal hydroxide + hydrogen. For example, sodium + water → sodium hydroxide + hydrogen, and the hydroxide makes the solution alkaline.
Why do alkali metals float on water?
Lithium, sodium and potassium float on water because they have a low density, less than that of water. Alkali metals are also soft enough to cut with a knife and have low melting points compared to other metals.
What colour does universal indicator go with alkali metals in water?
Universal indicator turns blue or purple, pH 12-14, after an alkali metal reacts with water, because the metal hydroxide formed makes the solution alkaline. Group 1 metals are named alkali metals for this reason.
Do alkali metals want to lose electrons?
Alkali metals do not 'want' to lose electrons; they lose them because the single outer electron is weakly held, far from the nucleus and shielded by inner electrons. Saying they 'want' to is a common exam mistake.