Atoms and Chemical Reactions
Everything you see is made of atoms - the smallest parts of elements that can't be broken down further. When different elements join together, they form compounds with completely new properties.
Chemical formulae tell you exactly what's in a compound and how many atoms of each element are present. In chemical equations, reactants go on the left side and products on the right. Here's the key rule: the total mass never changes during a reaction - what goes in must equal what comes out.
Mixtures are different from compounds because the substances aren't chemically bonded. You can separate mixtures using physical processes like filtration (for separating solids), crystallisation (for getting pure salts), and chromatography (for separating coloured substances).
Quick Tip: Remember that in reactions, atoms are just rearranged - they're never created or destroyed, which is why mass stays constant.
Scientists' understanding of atoms has evolved dramatically. Thomson discovered electrons and proposed the "plum pudding" model, but Rutherford's gold foil experiment showed that atoms have a tiny, dense nucleus. Today we know atoms contain protons (positive), neutrons (neutral), and electrons (negative) arranged in specific ways.
