C9.10654 · Section C9: Metals

Properties of metals

Key learnings

Physical properties: metals vs non-metals
Metals are generally good conductors of heat and electricity, malleable and ductile, with high melting and boiling points. Non-metals generally show the opposite of each: poor conductors, brittle, not ductile, low melting points. Malleable (hammered or pressed into shape without breaking) and ductile (drawn out into a wire without breaking) are two DISTINCT properties -- a material can be malleable without being ductile -- so both words are needed for full credit.
Metal + acid gives a salt and hydrogen
Metals above hydrogen in the reactivity series react with dilute acids: metal + acid gives a salt plus hydrogen. The ACID fixes the salt ending -- hydrochloric acid gives a chloride, sulfuric acid gives a sulfate, e.g. $\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2$ . The more reactive the metal, the faster and more vigorous the fizzing, so the rate of reaction with a dilute acid is itself evidence of a metal's position in the reactivity series.
Cold water gives a hydroxide, steam an oxide
Very reactive metals (sodium, calcium) react with cold water to give a metal hydroxide plus hydrogen: $2\text{Na} + 2\text{H}_2\text{O} \rightarrow 2\text{NaOH} + \text{H}_2$ . Observations: fizzing, the metal moving/floating across the surface, and for sodium melting into a ball from the heat released. Less reactive magnesium does not react with cold water but does react with steam, giving the oxide $\text{MgO}$ plus hydrogen.

Common mistakes

Drawn from real examiner reports.

Hydroxide (cold water) ≠ oxide (steam)

Cold water plus a very reactive metal gives a metal hydroxide ( $\text{NaOH}$ , $\text{Ca(OH)}_2$ ). Steam plus a less reactive metal gives a metal oxide ( $\text{MgO}$ ), never a hydroxide. Candidates routinely write "magnesium hydroxide" for the steam reaction, or calcium oxide for the cold-water one. Check the reagent first: only a cold-water product ends in -OH.

Flagged Jun 2022 P32 Q5a

"It reacts" is not an observation

A "describe what you observe" question needs specific observable evidence: fizzing/effervescence and gas (bubbles) released at minimum. For sodium or calcium in cold water, also credit the metal moving or floating on the surface, sodium melting into a ball, and the mixture warming. "A reaction happens" describes nothing and scores zero.

Flagged Jun 2022 P32 Q5a

"ZN" is not zinc -- symbol case matters

A chemical symbol is ONE capital letter, optionally followed by ONE lower-case letter: $\text{Zn}$ , $\text{Mg}$ , $\text{Na}$ , $\text{Ca}$ , $\text{Al}$ . "ZN" in all capitals is not a valid chemical symbol at all, and a wrongly-cased symbol is not credited as the correct element -- the equation is marked wrong even when the formulae and the balancing are perfect.

Flagged Nov 2022 P31 Q8diii

Magnesium chloride is MgCl2, not MgCl

Magnesium forms a 2+ ion, so it needs TWO chloride ions: $\text{MgCl}_2$ . Writing "MgCl" loses the formula mark and makes the equation impossible to balance. In the same equations, hydrogen released as a free element must be the diatomic molecule $\text{H}_2$ and never a lone "H" -- the same holds for $\text{O}_2$ and $\text{Cl}_2$ .

Sodium + water is not balanced 1:1

The equation $\text{Na} + \text{H}_2\text{O} \rightarrow \text{NaOH} + \text{H}_2$ is NOT balanced: one water molecule cannot supply both the two hydrogen atoms of $\text{H}_2$ and the OH of the hydroxide. Double all three species: $2\text{Na} + 2\text{H}_2\text{O} \rightarrow 2\text{NaOH} + \text{H}_2$ . Count every element on both sides before moving on.

Graphite conducts -- the non-metal exception

The metal/non-metal contrast states GENERAL patterns, and examiners expect the standard exception: graphite, a non-metal, is a good conductor of electricity. "No non-metal conducts" is wrong. The exception is electrical only -- graphite is still brittle, not ductile, and the other general non-metal properties are unaffected.

"Bendy" and "strong" score nothing

Comparison questions are marked on the precise terms. Use malleable for shaping by hammering or pressing, ductile for drawing into a wire, and brittle for a non-metal that shatters or crumbles. "Bendy", "flexible", "strong" and "tough" are not mark-scheme vocabulary, and answering with them wastes an otherwise correct comparison.

Exam tips

Let the reagent name the product
Read the reagent before writing anything. "Dilute acid" gives salt + hydrogen; "cold water" gives metal hydroxide + hydrogen; "steam" gives metal oxide + hydrogen. Write that general word equation first, then substitute the named metal, and only then convert to formulae.
Balance by inspection, then re-count
Convert every word to its correct formula (magnesium chloride is $\text{MgCl}_2$ because magnesium forms a 2+ ion), write free hydrogen, oxygen and chlorine as $\text{H}_2$ , $\text{O}_2$ and $\text{Cl}_2$ , then check that each element has the same total on both sides.
Answer the command word, not the topic
State wants the term alone; describe wants observable evidence; explain wants the reason behind it. Restating the observation for an "explain" earns nothing -- link reactivity to the energy available from cold water versus steam. Match your number of points to the mark tariff.
Quote the gas test in full
Where hydrogen is a product, do not just name it. Say how you would confirm it: hold a lit (burning) splint at the mouth of the test tube and listen for a squeaky pop. Giving the test without the positive result, or the result without the test, usually drops a mark.

Revision notes