CDS Chemistry · Formula sheet
Metals and Non-Metals formulas
1 formula, 8 reference tables and 12 common traps for CDS Chemistry Metals and Non-Metals, grouped by subtopic.
Properties of Metals, Non-Metals and Metalloids
Learn this subtopic in the notesPhysical properties of metals
| Property | Meaning | Example |
|---|---|---|
| Malleable and ductile | Beaten into sheets; drawn into wires | Gold, the best at bothQ |
| Sonorous | Rings when struck | School bellsQ |
| Lustrous | Shiny surface | Polished silver |
| Good conductor | Carries heat and electricity | Silver best, then copperQ CDS 2022 (II): silver and copper are the pair of very good heat conductors; lead and mercury are poor. |
Non-metals that break the rules, and metalloids
| Element | Kind | Notable property |
|---|---|---|
| Iodine | Non-metal | Lustrous (shiny)Q CDS 2021 (I): iodine is the non-metal that is lustrous. Silicon and germanium are metalloids, not non-metals. |
| Graphite | Non-metal (carbon) | Conducts electricity |
| Diamond | Non-metal (carbon) | Hardest natural substance |
| Germanium | Metalloid | SemiconductorQ |
| Silicon | Metalloid | Semiconductor |
| Boron, arsenic, antimony, tellurium | Metalloids | Properties of both metals and non-metals |
Common traps
Mercury is neither malleable nor ductile
Mercury is a liquid at room temperature, so it cannot be beaten or drawn. Among Na, Au, Ce and Hg, only gold is clearly both malleable and ductile.
Silicon and germanium are metalloids
When a question asks for a non-metal that shines, silicon and germanium are wrong: they are metalloids. The answer is iodine.
The Reactivity Series
Learn this subtopic in the notesDisplacement: a more reactive metal pushes out a less reactive one
Displacement rule
The reactivity series and reactions with acids
| Metal | Reaction with dilute HCl | Reaction with oxygen |
|---|---|---|
| K, Na, Ca | Violent | Burn readily |
| Mg | Fast; gives H₂ | Burns with a white flameQ CDS 2018 (II): magnesium with hydrochloric acid is the pair that gives hydrogen. |
| Al, Zn, Fe | Slower in that order; gives H₂ | Form oxides |
| Pb | Very slow | Forms an oxide |
| Cu | No reaction (below H) | Forms a black oxide when heated |
| Ag, Au | No reaction | Do not form an oxideQ CDS 2020 (II): silver is the metal that does not form an oxide with oxygen. |
Order with dilute HCl, asked in CDS 2021 (II) and 2024 (I): Mg > Al > Zn > Fe.
Why reactive metals are stored under oil
Common traps
Nitric acid rarely gives hydrogen
Nitric acid is an oxidising acid. Zinc or copper with nitric acid gives oxides of nitrogen, not hydrogen. Use HCl or dilute H₂SO₄ for the hydrogen test.
Zinc sits above iron
The order is Mg > Zn > Fe. A statement giving 'Mg > Fe > Zn' is wrong.
Only the higher metal displaces
Copper is below lead, so Cu + PbCl₂ → CuCl₂ + Pb does not happen. Fe, Zn and Mg are all above copper, so each displaces copper from copper sulphate.
Sodium is under kerosene because of moisture, not evaporation
Sodium does not evaporate. It is kept under kerosene because it reacts violently with moisture and oxygen in the air.
Extraction of Metals and Alloys
Learn this subtopic in the notesOres and how metals are extracted
| Metal | Main ore | Extracted by |
|---|---|---|
| Aluminium | Bauxite (Al₂O₃·2H₂O) | Electrolysis of aluminaQ |
| Sodium | Rock salt (NaCl) | Electrolysis of fused NaClQ CDS 2025 (II): sodium is the metal won by electrolysis of its molten compound. |
| Iron | Haematite (Fe₂O₃) | Reduction with coke in a blast furnace |
| Zinc | Zinc blende (ZnS) | Roasting, then reduction with carbon |
| Mercury | Cinnabar (HgS) | Roasting |
| Copper | Copper pyrites (CuFeS₂) | Roasting and smelting |
Common alloys and what they are made of
| Alloy | Made of | Used for |
|---|---|---|
| Solder | Lead and tin | Joining wires (low melting point)Q |
| Brass | Copper and zinc | Fittings, instruments |
| Bronze | Copper and tin | Statues, medals |
| Stainless steel | Iron, chromium, nickel | Utensils; does not rust |
| Duralumin | Aluminium, copper, magnesium, manganese | Aircraft bodies |
| Amalgam | Mercury with another metal | Dental fillings |
Common traps
Roasting is for sulphides, calcination for carbonates
Roasting heats a sulphide ore in excess air. Calcination heats a carbonate ore in limited air. Smelting is the later reduction to the metal.
Electrolysis is for the most reactive metals
Sodium, potassium, calcium, magnesium and aluminium are won by electrolysis of a molten compound. Copper and tin are reduced by smelting, and gold occurs free, so none of them needs it.
Brass has zinc, bronze has tin
Both are copper alloys. Brass = copper + zinc; bronze = copper + tin. Solder is lead + tin, with no copper.
Corrosion and Its Prevention
Learn this subtopic in the notesWhat each metal forms when it corrodes
Preventing corrosion, and anodising
| Method | How it protects |
|---|---|
| Painting, oiling | Keeps air and moisture away |
| Galvanising | Zinc coat corrodes first, protecting iron |
| Electroplating, tinning | Coat of a less reactive metal |
| Anodising | Aluminium as the anode; O₂ at the anode thickens the oxide filmQ CDS 2023 (I), HARD: 'oxygen gas is evolved at the cathode' was the false statement. |
Common traps
Silver does not form an oxide
Silver blackens because of sulphur, forming Ag₂S. Options naming silver oxide, silver carbonate or silver nitrate are wrong; so is the formula 'AgS'.
In anodising, oxygen forms at the anode
The aluminium is the anode, and oxygen is released there, where it combines with the metal to thicken the oxide film. Hydrogen comes off at the cathode.
Galvanising uses zinc, not tin
Galvanised iron is coated with zinc, which is more reactive than iron and corrodes first. A tin coat only shields the iron; once it is scratched, the iron rusts faster.