Basic Building Blocks and Separation Techniques

Elements are the pure substances where all atoms are identical - think of them as chemistry's alphabet. When two or more elements join chemically, you get a compound (like water, H₂O). Mixtures are different because the substances just sit together without chemically bonding - like oil and water.

Every atom has a chemical formula that tells you exactly what it contains. The atomic number shows how many protons (and electrons) it has, whilst the mass number includes neutrons too. For nitrogen, you've got 7 protons, 7 electrons, and 7 neutrons $14-7=7$.

Separating mixtures is dead useful in real life. Filtration traps solid particles that won't dissolve, letting liquid pass through filter paper. Crystallisation works for dissolved solids - just let the water evaporate and crystals form. Chromatography separates different substances because they move at different speeds up special paper.

Quick Tip: One spot on chromatography paper = pure substance, multiple spots = mixture!