Atoms, Elements and Compounds

Atoms are the smallest parts of any substance that can't be broken down chemically - think of them as nature's Lego blocks. Everything you see is made from these tiny particles, from the air you breathe to your mobile phone.

Elements contain only one type of atom and each has its own symbol, like Na for sodium or O for oxygen. When different types of atoms join together, they form compounds - substances with completely new properties from their original elements.

Naming compounds follows simple rules that'll save you loads of time in exams. If a compound contains just two elements, it ends in "-ide" (like sodium sulphide, Na₂S). When oxygen joins the party with two or more elements, the name ends in "-ate" (like sodium sulphate, Na₂SO₄).

Quick tip: The small numbers after element symbols (called subscripts) tell you exactly how many atoms of that element are present - Na₂SO₄ has 2 sodium atoms, 1 sulphur atom, and 4 oxygen atoms!

Separating Mixtures

Mixtures are different from compounds because the substances aren't chemically stuck together - they're just mixed up like ingredients in a salad. This means you can separate them using physical techniques that every chemist needs to master.

Filtration works brilliantly when you need to separate something that dissolves from something that doesn't. Imagine separating sand from salty water - the salt solution passes through filter paper whilst the sand gets trapped.

Simple distillation separates liquids by heating them until they evaporate, then cooling the vapour back into liquid. It's perfect for getting pure water from seawater. Crystallisation removes dissolved substances by heating the solution until crystals form as the solvent evaporates.

Chromatography separates small amounts of dissolved substances by letting a solvent carry them up absorbent paper at different speeds. You've probably seen this technique used to separate the different colours in black ink - it's like a chemical race where different substances move at different speeds!