Structure and bonding · GCSE Chemistry
Group 1 alkali metals
GCSE Chemistry revision on Group 1 alkali metals: one outer electron, reactions with water and oxygen, and why reactivity increases down the group.
One outer electron, stored under oil, fizz with water to make an alkaline hydroxide and hydrogen. Down the group the outer electron is further away and more shielded, so it is lost more easily.
The important bits
What you need to know
- 1
Group 1 metals (Li, Na, K, Rb, Cs) have one electron in the outer shell: Li 2,1; Na 2,8,1; K 2,8,8,1. They form 1+ ions: Li⁺, Na⁺, K⁺.
- 2
They are soft, low-density metals, stored in oil to keep air and water away. Melting point decreases down the group as metallic bonding gets weaker in larger atoms.
- 3
Reaction with water: 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g). The solution is alkaline (turns universal indicator purple) because of OH⁻(aq).
- 4
Lithium: fizzes steadily. Sodium: melts into a ball, fizzes rapidly. Potassium: melts, hydrogen ignites with a lilac flame. Observations must match the metal.
- 5
Reaction with oxygen: 4Na(s) + O₂(g) → 2Na₂O(s). The oxide is a basic ionic oxide; with water it makes the hydroxide. Lithium forms Li₂O; sodium also forms peroxide in excess oxygen (Triple detail).
- 6
Reaction with chlorine: 2Na(s) + Cl₂(g) → 2NaCl(s). White ionic salts, NaCl, KCl, LiCl, all containing the 1+ metal ion and Cl⁻.
- 7
Reactivity increases down Group 1. There are more shells, so the outer electron is further from the nucleus and more shielded by inner electrons. Attraction decreases and the electron is lost more easily.
- 8
The nuclear charge increases down the group, but distance and shielding dominate at GCSE. Do not write “it wants to lose an electron more”. Give the particle reason.
Quotations worth analysing
Short evidence. Real method.
“2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g)”
Metal hydroxide and hydrogen every time. The hydroxide makes the solution alkaline — that is why they are alkali metals. State symbols: solid metal, liquid water, aqueous alkali, hydrogen gas.
“Na → Na⁺ + e⁻”
Every Group 1 reaction is the loss of that outer electron. Down the group this happens more readily, so reactions are more vigorous.
“Electronic structures: Li 2,1 Na 2,8,1 K 2,8,8,1”
Same outer electron count means similar reactions. Extra inner shells mean the outer electron is lost more easily down the group.
Go deeper
Write observations that could only be that metal
“It fizzed” could be any of them. Lithium does not melt; sodium does melt and moves as a ball; potassium’s hydrogen burns with a lilac flame and the reaction is violent. Universal indicator in the solution goes blue/purple for all three because OH⁻ is produced. A squeaky pop tests for hydrogen. If the metal is left in air, a dull oxide layer forms. Those details are method marks on a demonstration question. Then attach the equation. Students remember the fizz and forget NaOH. The alkali is the reason for the group name and the pH mark.
Go deeper
The trend is shielding and distance, not “they want to”
Potassium’s outer electron is in the fourth shell. Inner electrons shield it from the nucleus, and it is further away than sodium’s outer electron. Electrostatic attraction is weaker, so the electron is lost more easily and reactivity rises. Lithium is the least reactive of the three you meet, not because it “does not want” to react, but because its outer electron is closest and least shielded. Compare with Group 7, where the atom must gain an electron: extra shells make that harder, so halogen reactivity falls down the group. Same physics, opposite trend, because one group loses and the other gains.
Go deeper
Ionic compounds, not molecules
Na₂O, NaCl and NaOH are giant ionic. Sodium does not share its electron with chlorine; it transfers it. The hydroxide ion is OH⁻, a compound ion, so the formula is NaOH not Na₂OH. When sodium burns in chlorine you see an orange flame and white salt. When it burns in air the product is mainly sodium oxide. These are the same 1+ ion each time. If a question asks why Group 1 metals are similar, say one outer electron, 1+ ions, same type of ionic compounds — then give one equation as evidence.
See the idea in action
Explain why potassium reacts more vigorously with water than lithium, and write the equation for potassium. Potassium has more electron shells, so its outer electron is further from the nucleus and more shielded. The electron is lost more easily: K → K⁺ + e⁻. Equation: 2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g). The solution contains OH⁻ so it is alkaline. Lithium has only two shells, so its outer electron is held more strongly and the reaction is slower.
Exam technique
Turn knowledge into marks
For water reactions, write metal + water → metal hydroxide + hydrogen, include state symbols, and mention the alkaline solution. For the trend, use more shells, greater distance, more shielding, electron lost more easily.
Common mistakes
Do not give these marks away
- 01
Writing that potassium is more reactive because it has more electrons to lose, or because atoms “want” to react.
- 02
Giving the product as potassium oxide with water, or forgetting hydrogen.
- 03
Saying Group 1 metals are unreactive, or storing them in water in an exam answer.
Why does reactivity increase down Group 1?
AThe atoms have fewer protons
BThe outer electron is further from the nucleus and more shielded, so it is lost more easily
CThe metals have a full outer shell
DThe nuclear charge decreases down the group
Show the answer
The outer electron is further from the nucleus and more shielded, so it is lost more easily. Extra inner shells increase distance and shielding. Attraction to the outer electron falls, so it is lost more readily and reactions with water and oxygen become more vigorous.
Quick questions
If this is the bit you searched
What is the reaction of sodium with water GCSE Chemistry?
2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g). Sodium fizzes, melts into a ball, and the solution is alkaline because of hydroxide ions.
Why are Group 1 metals called alkali metals?
They react with water to form metal hydroxides, which are alkalis. The solutions contain OH⁻(aq) and have pH well above 7.
Why does potassium react faster than lithium?
Potassium’s outer electron is in a shell further from the nucleus and is more shielded, so it is lost more easily than lithium’s outer electron.
What ion do Group 1 metals form?
A 1+ ion, for example Na⁺, by losing their single outer electron to achieve a full outer shell.