Comprehensive guide covering the chemical and physical properties of metals, reactivity, extraction, and corrosion.

Structure and position The Periodic Table arranges elements in order of increasing proton number. Horizontal rows are periods; vertical columns are groups. Elements in the same group have similar chemical properties because they have the same number of outer-shell electrons. Across a period, metallic character generally decreases and non-metallic character increases. Position predicts electronic configuration, ion charge, reactivity, and physical properties. Group I atoms lose one outer electron to form $+1$ ions; Group VII atoms gain one electron to form $-1$ ions, because both processes produce a full outer shell. ...

Acids, bases and alkalis Acids react with metals, bases, and carbonates. $$\text{acid}+\text{metal} \rightarrow \text{salt}+\text{hydrogen}$$ $$\text{acid}+\text{base} \rightarrow \text{salt}+\text{water}$$ $$\text{acid}+\text{carbonate} \rightarrow \text{salt}+\text{water}+\text{carbon dioxide}$$ A base is usually a metal oxide or hydroxide that neutralises an acid. An alkali is a soluble base. Bases react with acids and ammonium salts: $$\text{base}+\text{ammonium salt} \rightarrow \text{salt}+\text{water}+\text{ammonia}$$ In aqueous solution, acids contain $\mathrm{H^+}$ ions and alkalis contain $\mathrm{OH^-}$ ions. Acids are proton donors; bases are proton acceptors. Strong acids such as hydrochloric acid dissociate completely, while weak acids such as ethanoic acid dissociate partially. ...

Physical and chemical changes A physical change does not produce a new substance; changes of state are physical changes. A chemical change produces one or more new substances. Reversibility, colour change, gas formation, temperature change, or a precipitate may provide evidence, but none alone is a complete definition. Rates of reaction The rate of reaction is how quickly reactants are used or products are formed. It can be measured by mass loss, gas volume, colour change, or precipitate formation over time. ...

Exothermic and endothermic reactions An exothermic reaction transfers heat to the surroundings. The surroundings warm and the enthalpy change is negative, so $\Delta H < 0$. An endothermic reaction takes in heat from the surroundings. The surroundings cool and the enthalpy change is positive, so $\Delta H > 0$. Examples include combustion and neutralisation for exothermic reactions, and thermal decomposition and photosynthesis for endothermic reactions. Reaction pathway diagrams A reaction pathway diagram plots energy vertically and reaction progress horizontally. ...