Elements, Compounds, Mixtures and Alloys

<h3>Sorting matter</h3><p><strong>Elements</strong> are the building blocks of matter. There are about 119 known elements, each made of only one kind of atom and listed on the <strong>periodic table</strong>. Examples include iron, oxygen and gold.</p><p>A <strong>compound</strong> is formed when elements are <strong>chemically combined</strong> in a fixed proportion. The properties of a compound are different from the elements that made it. Water (H₂O) is a compound of hydrogen and oxygen.</p><p>A <strong>mixture</strong> is two or more substances combined <strong>physically</strong>, not chemically. The substances keep their own properties and can be separated by methods such as filtering, evaporation or using a magnet.</p><h3>Alloys</h3><p>An <strong>alloy</strong> is a mixture made by combining a metal with one or more other elements. Alloys keep useful metal properties like conducting electricity and shininess, but they are engineered to be <strong>harder, stronger or more resistant to corrosion</strong>. Common examples are steel (iron + carbon), brass (copper + zinc) and bronze (copper + tin).</p><ul><li><strong>Aluminium</strong> &mdash; light and resists rust; used for roofing and aircraft.</li><li><strong>Iron and steel</strong> &mdash; strong; used for construction and tools.</li><li><strong>Zinc</strong> &mdash; coats steel (galvanising) to stop rust.</li></ul><div class="callout"><strong>Kenyan context:</strong> The galvanised <em>mabati</em> roofing sheets seen across Kenya are steel coated with a thin layer of zinc. The zinc corrodes first and protects the iron underneath, which is why a good mabati roof can last for many years even in the rainy highlands.</div>