Physical properties of metals
Most metals conduct electricity and heat, are malleable (beaten into sheets), ductile (drawn into wires), shiny, dense, with high melting and boiling points; nearly all are solid at room temperature. Learn the exceptions: mercury is the only metal liquid at room temperature; sodium and potassium are so low in density they float on water; and graphite, a non-metal, conducts electricity, so conduction alone does not prove a metal.
Chemical reactions of metals
Metals react in three ways. With oxygen they burn to basic oxides (); gold, silver and platinum barely react. Potassium, sodium and calcium react with cold water to give a hydroxide + hydrogen; magnesium and iron only with steam, giving an oxide + hydrogen; copper not at all. With dilute acids, metals above hydrogen give a salt + hydrogen; copper, silver and gold (below hydrogen) do not. Hydrogen gives a squeaky pop.
(Extended) Metallic bonding and alloys
A metal is a lattice of positive ions in a sea of mobile (delocalised) electrons, held by their attraction. Mobile electrons carry charge and heat; layers of ions slide, so it is malleable and ductile; strong attraction gives high melting points. Use "mobile" or "delocalised" — "free" earns nothing. An alloy is a mixture, not a compound; atoms of different sizes disrupt the lattice so layers cannot slide, making it harder than the pure metal (steel, brass, bronze).
Drawn from real examiner reports.
(Extended) Metallic bonding: mobile not free
"Free electrons" gains no credit — write "mobile" or "delocalised" electrons. "Atoms" is also wrong: once they lose their outer electrons the particles are positive ions. The minimum answer is a lattice of positive ions [1] plus mobile/delocalised electrons [1], with the electrostatic attraction between them earning a third mark.
W22 P41 Q2(a); S22 P31 Q3(a); S22 P41 Q3(a) — free electrons gains no credit; mobile/delocalised electrons and the lattice of positive ions are required.
(Extended) Alloys are mixtures, not ordered
Shown a diagram of an alloy, students pick the neat regular array — but that is a pure metal. An alloy is a mixture, not a compound: atoms of different sizes in a disrupted lattice, no fixed formula. The differently-sized atoms stop layers sliding, so it is harder. Choose the picture with mostly one size of circle and a few different ones scattered at random.
W22 P32 Q2(d)(iii); S23 P31 Q5(c)(i) — students select an ordered lattice instead of the randomly-mixed structure; alloys must be described as mixtures, not compounds.
Observations, not product names
When a question asks what you observe, describe what can be seen, heard or felt — not the products. "Zinc chloride is formed" scores zero for an observation mark. Correct observations for a metal + acid reaction: bubbles/fizzing/effervescence; the solid dissolves or gets smaller; the mixture warms up. Keep product names for "name the products" questions.
W22 P31 Q6(a); W22 P42 Q4(b); S23 P31 Q4(d)(ii) — students give product names instead of observable changes (bubbles, fizzing, dissolving).
Steam vs cold water for Mg and Fe
Do not say magnesium or iron "reacts vigorously with cold water" — they barely react with cold water and react only with steam. The product differs too: cold water gives a hydroxide + hydrogen (K, Na, Ca); steam gives an oxide + hydrogen (Mg → MgO, Fe → ). Match the metal to the right conditions and the right product before writing an equation.
Metals below hydrogen do not react
Not every metal fizzes in acid. Only metals above hydrogen in the reactivity series react with dilute acids to give a salt and hydrogen; copper, silver and gold are below hydrogen and give no reaction — no bubbles, no salt. Copper likewise does not react with water or steam. Explain its non-reaction as "below hydrogen, not reactive enough to displace it".
Physical vs chemical properties
"Reacts with acid" or "burns in oxygen" are chemical, not physical, properties. Physical properties describe the substance with no chemical change — conducting electricity and heat, malleable, ductile, shiny, dense, high melting point. For physical properties do not offer a reaction; for chemical properties, name a reaction with oxygen, water or acid.
Three steps for metal equations
Write metal-reaction equations in three steps: (1) products — acid → salt + hydrogen, cold water → hydroxide + hydrogen, steam → oxide + hydrogen; (2) formulae, salt set by metal charge, hydrogen as ; (3) balance, then state symbols.
Metal charges build the salt
Build the salt from the metal ion charge: Na+ gives NaCl and Na2SO4; Mg2+, Zn2+, Fe2+ and Ca2+ each give an MCl2 chloride and an MSO4 sulfate. Chloride is −1 and sulfate 2−, so a 2+ metal takes two chlorides but only one sulfate. Fix the formula first, then balance.
Test hydrogen; describe observations
To identify the gas, hold a lighted splint at the tube mouth — a squeaky pop confirms hydrogen. To describe the reaction, use observation words: fizzing/effervescence, solid dissolving, mixture warming. Never name products for an observation mark.
Metal — a substance that is typically a solid at room temperature (exception: mercury is a liquid), conducts electricity and heat, is malleable and ductile, and has a shiny appearance.
Malleable — can be beaten into sheets without shattering.
Ductile — can be drawn into wires without breaking.
Metallic bonding (Extended) — the electrostatic attraction between a lattice of positive ions and a sea of mobile (delocalised) electrons surrounding them. The electrons are released by the metal atoms into a shared "sea" that extends throughout the structure.
Alloy (Extended) — a mixture (not a compound) of a metal with one or more other elements (usually other metals), in which atoms of different sizes disrupt the regular lattice.
Define malleable as a property of metals.
Sodium reacts with cold water.
(a) Write a balanced symbol equation for this reaction. Include state symbols.
(b) State the test for the gas produced in this reaction and the result you would expect.
