Metals and Nonmetals Class 10 Science Chapter 3 - Physical Properties of Metals and Non-Metals

Metals and Non-metals: Physical Properties, Chemical Reactions, and Reactivity

Elements are broadly classified into metals and non-metals based on their physical and chemical properties. This chapter in CBSE Class 10 Science covers the distinguishing characteristics of each category, the chemical reactions they undergo, the reactivity series of metals, and how metals are extracted from their ores. Understanding these concepts is essential for appreciating the role of materials in everyday life, from the iron in bridges and the copper in electrical wiring to the carbon in pencils and the oxygen we breathe.

Metals are typically hard, lustrous (shiny), malleable (can be hammered into thin sheets — gold is the most malleable), ductile (can be drawn into wires — copper and silver are the most ductile), good conductors of heat and electricity (silver is the best, followed by copper), and have high melting and boiling points (tungsten has the highest melting point of any metal). Metals are solid at room temperature, except mercury which is a liquid. Non-metals, in contrast, are generally brittle, non-lustrous (iodine is an exception — it is lustrous), poor conductors of heat and electricity (graphite, a form of carbon, is an exception — it conducts electricity), and exist as solids, liquids (bromine), or gases at room temperature. Metalloids like silicon and germanium exhibit intermediate properties and are used in semiconductor electronics. Chemically, metals lose electrons to form positive ions (cations): Na → Na⁺ + e⁻. Metals react with oxygen to form basic oxides (2Mg + O₂ → 2MgO), with water to produce metal hydroxides and hydrogen gas (2Na + 2H₂O → 2NaOH + H₂↑), and with dilute acids to produce salt and hydrogen (Zn + H₂SO₄ → ZnSO₄ + H₂↑). Non-metals gain or share electrons to form negative ions (anions) or covalent compounds. Non-metal oxides are generally acidic (CO₂ + H₂O → H₂CO₃).

The reactivity series arranges metals in order of decreasing reactivity: K > Na > Ca > Mg > Al > Zn > Fe > Pb > [H] > Cu > Hg > Ag > Au. Potassium is the most reactive and gold is the least. Metals above hydrogen in the series can displace hydrogen from dilute acids; metals above another metal can displace it from its salt solution (e.g., Fe + CuSO₄ → FeSO₄ + Cu). This principle is used in displacement reactions and helps predict whether a reaction will occur. The extraction of metals from their ores depends on their position in the reactivity series. Highly reactive metals (Na, K, Ca, Al) are extracted by electrolysis of their molten salts. Moderately reactive metals (Zn, Fe, Pb, Cu) are extracted by reduction of their oxides with carbon (coke) in a blast furnace — this is called smelting. Less reactive metals (Hg, Ag) can be obtained by heating their ores alone, as they decompose easily. The extraction of iron from haematite (Fe₂O₃) in a blast furnace involves three steps: washing and concentration of the ore, reduction by carbon monoxide (Fe₂O₃ + 3CO → 2Fe + 3CO₂), and removal of impurities as slag (CaCO₃ → CaO + CO₂, then CaO + SiO₂ → CaSiO₃). Corrosion — the slow deterioration of metals by environmental action — can be prevented by painting, greasing, galvanising (coating with zinc), alloying (mixing with other metals), and chrome-plating. Alloys like steel (iron + carbon), stainless steel (iron + chromium + nickel), brass (copper + zinc), and bronze (copper + tin) have superior properties compared to their constituent metals.

• Metals are malleable, ductile, lustrous, and good conductors; non-metals are brittle, dull, and poor conductors (with notable exceptions).
• Metals form basic oxides and cations; non-metals form acidic oxides and anions or share electrons covalently.
• The reactivity series (K > Na > ... > Au) predicts displacement reactions and extraction methods.
• Extraction methods depend on reactivity: electrolysis for reactive metals, smelting with carbon for moderately reactive ones.
• Corrosion prevention: painting, galvanising, alloying; alloys (steel, brass, bronze) have improved properties over pure metals.