Class 10 Science · Chapter 3 NotesMetals and Non-metals

Metals in their pure state have a shining surface, called metallic lustre. They are generally hard, though hardness varies from metal to metal. Metals can be beaten into thin sheets, which is malleability, and drawn into thin wires, which is ductility. Gold and silver are the most malleable metals, and gold is the most ductile metal. Metals are good conductors of heat and electricity, and they are sonorous, meaning they produce a sound when struck. Non-metals are usually solids or gases, except bromine which is a liquid. They are generally not lustrous, not malleable or ductile, and are poor conductors of heat and electricity. However, there are exceptions: mercury is a liquid metal at room temperature, gallium and caesium melt on the palm, iodine is a lustrous non-metal, and graphite, an allotrope of carbon, conducts electricity. Alkali metals such as lithium, sodium and potassium are soft enough to be cut with a knife.

• Malleabilityability to be beaten into thin sheets
• Ductilityability to be drawn into thin wires
• Sonorousmetals that produce sound on striking a hard surface
• Best conductors of heatsilver and copper; poor conductors: lead and mercury
• Exceptiongraphite is a non-metal that conducts electricity

Metals react with oxygen to form metal oxides, which are generally basic. For example, copper heated in air forms black copper(II) oxide, and aluminium forms aluminium oxide. Some oxides such as aluminium oxide and zinc oxide are amphoteric, reacting with both acids and bases to form salt and water. Sodium oxide and potassium oxide dissolve in water to form alkalis. Metals such as potassium and sodium react so vigorously with oxygen that they catch fire in open air, so they are stored in kerosene. Metals also react with water: potassium and sodium react violently with cold water, calcium reacts less violently and starts floating, magnesium reacts with hot water, and metals like aluminium, iron and zinc react with steam. Lead, copper, silver and gold do not react with water. With dilute acids, metals give salt and hydrogen gas. The reactivity order with dilute hydrochloric acid is Mg > Al > Zn > Fe, while copper does not react. Nitric acid does not usually give hydrogen because it is a strong oxidising agent, though magnesium and manganese can evolve hydrogen with very dilute nitric acid.

• Metal + Oxygen → Metal oxide (generally basic)
• Metal + Water → Metal oxide/hydroxide + Hydrogen
• Metal + Dilute acid → Salt + Hydrogen
• Amphoteric oxidesaluminium oxide and zinc oxide
• Aqua regia3 parts concentrated HCl and 1 part concentrated HNO3, dissolves gold

A more reactive metal can displace a less reactive metal from its compound in solution or molten form. This is called a displacement reaction. For example, if an iron nail is placed in copper sulphate solution, iron displaces copper because iron is more reactive. The reactivity series arranges metals in decreasing order of reactivity: potassium, sodium, calcium, magnesium, aluminium, zinc, iron, lead, hydrogen, copper, mercury, silver and gold. Metals above hydrogen in the series can displace hydrogen from dilute acids. This series helps predict whether a given displacement reaction will occur and is also used to decide how a metal can be extracted from its ore.

• Metal A + Salt solution of B → Salt solution of A + Metal B (if A is more reactive than B)
• Reactivity orderK > Na > Ca > Mg > Al > Zn > Fe > Pb > [H] > Cu > Hg > Ag > Au
• Metals above hydrogen displace hydrogen from dilute acids
• Displacement reactions provide evidence of relative reactivity

Metals tend to lose electrons to attain a stable noble gas configuration, forming positively charged ions called cations. Non-metals tend to gain electrons to form negatively charged ions called anions. For example, sodium loses one electron to form Na⁺, and chlorine gains one electron to form Cl⁻. The oppositely charged ions attract each other by strong electrostatic forces and form ionic or electrovalent compounds such as sodium chloride. Magnesium loses two electrons to form Mg²⁺, and two chloride ions are needed to form MgCl₂. Ionic compounds are generally solids, somewhat hard and brittle. They have high melting and boiling points because a lot of energy is needed to break the strong inter-ionic attraction. They are usually soluble in water and insoluble in kerosene or petrol. In the solid state they do not conduct electricity because ions cannot move, but in molten state or in solution they conduct electricity because the ions become free to move.

• Cationpositively charged ion formed by loss of electrons
• Anionnegatively charged ion formed by gain of electrons
• Ionic compoundshigh melting and boiling points, brittle, water-soluble
• Conduct electricity in molten state or in aqueous solution, not in solid state

The earth's crust is the major source of metals. Elements or compounds that occur naturally in the earth's crust are called minerals. A mineral that contains a high percentage of a particular metal and from which the metal can be profitably extracted is called an ore. Metals at the bottom of the activity series, such as gold, silver, platinum and copper, are found in the free state. Metals at the top, such as potassium, sodium, calcium, magnesium and aluminium, are never found free because they are very reactive. Metals in the middle, such as zinc, iron and lead, occur mainly as oxides, sulphides or carbonates. Extraction involves several steps: enrichment of ore to remove gangue, conversion of sulphide and carbonate ores to oxides by roasting or calcination, reduction of the oxide to metal, and refining. Metals low in the series can be obtained by heating their oxides alone. Metals in the middle are reduced using carbon or by displacement with more reactive metals. Metals high in the series are obtained by electrolytic reduction of their molten chlorides or oxides. Electrolytic refining is widely used to purify metals such as copper, zinc, tin, nickel, silver and gold.

• Mineralnaturally occurring element or compound in the earth's crust
• Oremineral from which a metal can be profitably extracted
• Gangueimpurities such as soil and sand present in ore
• Roastingheating sulphide ore strongly in excess air to form oxide
• Calcinationheating carbonate ore strongly in limited air to form oxide
• Thermit reactionFe₂O₃ + 2Al → 2Fe + Al₂O₃ + Heat, used to join railway tracks
• Electrolytic refiningimpure metal as anode, pure metal as cathode, metal salt solution as electrolyte

Corrosion is the gradual eating away of a metal surface by the action of air, moisture or chemicals. Silver articles become black due to a coating of silver sulphide. Copper reacts with moist carbon dioxide to form basic copper carbonate, which is green. Iron rusts when exposed to moist air, forming a brown flaky coating. Rusting requires both air and water. The rusting of iron can be prevented by painting, oiling, greasing, galvanising, chrome plating, anodising or making alloys. Galvanisation is coating iron or steel with a thin layer of zinc. Alloying is a method of improving the properties of a metal by mixing it with other elements. An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal. For example, stainless steel is an alloy of iron with nickel and chromium, and brass is an alloy of copper and zinc. If one of the metals in an alloy is mercury, it is called an amalgam.

• Corrosionslow deterioration of a metal by air, moisture or chemicals
• Rusting of iron needs both air and moisture
• Galvanisationcoating iron or steel with zinc
• Alloyhomogeneous mixture of two or more metals, or a metal and a non-metal
• Amalgamalloy in which one metal is mercury
• 24 carat gold is pure and soft; 22 carat gold is alloyed with silver or copper