Li, Na, K react the same → one family
Group 1 (alkali metals) are reactive metals: lithium, sodium and potassium. They all react with water the same way: the metal floats, moves and fizzes as hydrogen is given off, and an alkaline metal hydroxide solution forms (indicator turns blue/purple). General equation: They react alike, so they are one family (spec 2.1).
Reactivity increases down Group 1
The differences in how vigorously Li, Na and K react give the reactivity trend (spec 2.2): reactivity increases down the group. In water, lithium fizzes and moves slowly; sodium melts into a ball and moves faster; potassium reacts so fast the heat ignites the hydrogen (a lilac flame). In air they tarnish. The trend lets you predict (spec 2.3) rubidium reacts even more violently, francium most of all.
Why reactivity rises: the outer electron
Every Group 1 atom has one electron in its outer shell and reacts by losing it to form a ion (). Down the group, atoms have more shells, so the outer electron is further from the nucleus and more shielded. The attraction between nucleus and outer electron is weaker, so the single outer electron is lost more easily — more reactive (spec 2.4C).
Drawn from real examiner reports.
"Hydrogen formed" is a deduction, not seen
For observations when an alkali metal reacts with water, describe what you see or hear: fizzing, the metal floating and moving on the surface, getting smaller and disappearing, and (for K) a lilac flame. "Hydrogen is given off" is a conclusion from the fizzing — not an observation, so it scores nothing on an observation question.
November 2024 Paper 2C Q4(a)(i): "hydrogen was formed" was not credited as an observation (it is a deduction); credited answers were fizzing or the lithium moving on the surface.
Match the observation to the metal
Observations differ between the metals, so match them to the one named. For lithium, "a flame" and "melts into a ball" are not accepted — that is sodium/potassium behaviour; lithium fizzes steadily and moves on the surface. Give observations that fit the specific metal, and never re-state anything already in the stem.
November 2024 Paper 2C Q4(a)(i): candidates lost marks for writing "a flame" or "melts into a ball" for lithium (not correct); credited answers were fizzing or the lithium moving on the surface.
Say the SINGLE outer electron
Group 1 atoms lose only the single outer electron to form a ion. Explaining the trend, do not say "electrons are lost more easily" (plural) — the mark needs the one outer electron. Saying "more electrons" that are "lost more easily" is wrong: each atom only ever loses one electron, however far down the group it is.
June 2024 Paper 2C Q1(b): "electrons can be lost more easily" (plural) was not allowed — only the single outer electron is lost; this third mark was frequently missed.
Restating the trend is not explaining it
An "explain" question needs a mechanism, not a restatement. "Potassium is more reactive" just repeats the trend — no marks. You must link to the outer shell / outer electron: more shells → outer electron further from the nucleus → weaker attraction → lost more easily. Marks are lost for omitting the outer shell or referring to electrons wrongly.
November 2024 Paper 2C Q4(c)(ii): "potassium is more reactive" alone was not creditworthy; marks were lost for omitting the outer shell or mentioning electrons wrongly.
Solution is alkaline, not acidic/red
The product of a Group 1 metal and water is a metal hydroxide (e.g. ), giving an alkaline solution — universal indicator turns blue/purple. A common error is to say the solution is acidic and turns the indicator red, losing both the colour mark and the alkali mark. The name "alkali metals" is the clue: their hydroxides are alkalis.
November 2024 Paper 2C Q4(a)(ii): most knew the colour was blue/purple and the solution alkaline, but a few thought it was red and acidic and lost both marks.
Group 1 ≠ Group 2 (alkaline earth)
Do not confuse the alkali metals with the alkaline earth metals. Group 1 (Li, Na, K) are the alkali metals — one outer electron, forming ions. Group 2 are the alkaline earth metals, with two outer electrons. This topic is Group 1 only — use "alkali metal", not "alkaline earth metal".
(common Edexcel chemistry error)
The four-link reactivity chain
For a Group 1 reactivity "explain" (3 marks), give every link: more shells down the group → outer electron further from the nucleus → weaker attraction → single outer electron lost more easily. Always name the outer, single electron.
Give observations, not conclusions
When asked for observations, write only what you see or hear — fizzing, the metal floating and moving, getting smaller, a lilac flame (K). Do not write "hydrogen is produced" or "an alkali forms": those are conclusions, credited only if the products are asked for.
Predicting other alkali metals
To predict a lower member (spec 2.3), extend the trend: more shells → outer electron lost even more easily → more reactive. So rubidium reacts with water even more violently than potassium, caesium/francium more still. State "more vigorous" and justify with the trend.
The alkali metals are the elements in Group 1 of the periodic table. You must know lithium (), sodium () and potassium (), their reactions with water and air, the reactivity trend down the group, and how to explain that trend with electronic configuration.
Define the alkali metals (Group 1) in terms of their electronic structure.
Sodium reacts with water to form sodium hydroxide and hydrogen.
Write the balanced chemical equation for this reaction.
