Chapter 3 Metals and Non-Metals

Metals and non-metals differ significantly in their physical properties. Metals are generally lustrous (shiny), hard, malleable (can be beaten into sheets), ductile (can be drawn into wires), and good conductors of heat and electricity. They also have high melting and boiling points and high densities. For example, iron, copper, and gold show these properties. Non-metals, on the other hand, are generally dull, brittle, poor conductors (except graphite), and have lower melting points. Sulphur, phosphorus, and iodine are typical non-metals. However, there are exceptions — sodium and potassium are soft metals, mercury is liquid at room temperature, and diamond (a form of carbon) is extremely hard despite being a non-metal.

The reactivity series is a list of metals arranged in decreasing order of their chemical reactivity. From most reactive to least, it runs: potassium, sodium, calcium, magnesium, aluminium, zinc, iron, lead, hydrogen, copper, silver, gold, and platinum. This series helps predict which metals can displace others from their compounds. A more reactive metal always displaces a less reactive metal from its salt solution. For example, zinc displaces copper from copper sulphate solution. Metals above hydrogen in the series react with dilute acids to release hydrogen gas, while those below (like copper, silver, and gold) do not. The reactivity series also guides the choice of extraction methods — highly reactive metals require electrolysis while less reactive ones can be extracted by reduction.

Metal extraction from ores involves several steps depending on the reactivity of the metal. First, the ore is concentrated by removing gangue (impurities) through methods like hydraulic washing, froth flotation, or magnetic separation. Next, the concentrated ore is converted into metal oxide through roasting or calcination. Then, the oxide is reduced to obtain the metal — less reactive metals like copper can be reduced by heating alone; moderately reactive metals like iron and zinc require reduction with carbon or carbon monoxide. Highly reactive metals like sodium, potassium, and aluminium are extracted using electrolysis because carbon cannot reduce their oxides. Finally, the crude metal undergoes refining through processes like electrolytic refining to obtain pure metal.

Corrosion is the gradual deterioration of metals due to their reaction with substances in the environment such as oxygen, moisture, and acids. The most common example is rusting of iron: when iron is exposed to oxygen and water, it forms hydrated iron oxide, which is the reddish-brown rust. Corrosion weakens structures, damages machinery, and costs industries billions of rupees every year. Prevention methods include painting, oiling, or greasing the metal surface to block contact with moisture and air. Galvanisation — coating iron with zinc — protects because zinc is more reactive and corrodes first (sacrificial protection). Alloying iron with chromium and nickel creates stainless steel, which resists corrosion. Electroplating with chromium or silver also provides a protective coating.

Ionic compounds are formed when metals transfer electrons to non-metals, resulting in the formation of oppositely charged ions that attract each other. Metals tend to lose electrons to form positively charged cations, while non-metals tend to gain electrons to form negatively charged anions. The electrostatic force of attraction between these oppositely charged ions forms an ionic bond. For example, sodium (Na) gives one electron to chlorine (Cl), forming Na⁺ and Cl⁻, which combine to form sodium chloride (NaCl). Ionic compounds have high melting and boiling points due to strong ionic bonds, conduct electricity when dissolved in water or melted (because ions become free to move), and are generally soluble in water. They exist as crystalline solids at room temperature.