Metals and Non-Metals Class 10 Notes

The physical properties of this chapter are best learned as a comparison, because the board almost always asks for a difference and the answer is a pair of statements rather than a description. Every difference has a matching pair: lustrous against dull, malleable against brittle, ductile against brittle, sonorous against not sonorous, good conductor against poor conductor.Two properties are worth an extra sentence because they are not obvious. The sonorous property is tested by striking a metal and listening to the ringing sound, and it is why a metal plate is used as a bell. The density comparison is not universal, so in an answer the safe claim is that metals are generally denser than non-metals, with sodium as the exception the examiner may quote.

• Lustre: metals have a shining surface, while non-metals have a dull surface, with the exception of iodine, which is the one lustrous non-metal.
• State: metals are solid at room temperature and are exceptions such as mercury, which is liquid, while non-metals include both solids and the gases of the air.
• Malleability and ductility: metals can be beaten into sheets and drawn into wires, while solid non-metals are brittle and shatter.
• Sonority: metals ring when struck and are used in bells and plates, while non-metals do not ring and are used as clappers and hammers instead.
• Conductivity: metals conduct heat and electricity well and are used for wires and cooking utensils, while non-metals are poor conductors and are used for electric switches and handles.

Chemically, metals are the more reactive family, and their reactions divide into a small number of patterns: with oxygen to give oxides, with water, with dilute acids to give hydrogen, and with a salt solution of a less reactive metal to displace it. Non-metals are less reactive, and their characteristic reactions are with metals, with oxygen to give acidic or neutral oxides, and with hydrogen to give hydrides.The reactivity series is the ranking that turns these reactions into predictions. It is arranged from the most reactive to the least, and every question of the form which metal will displace which depends on reading two positions off it.

• With air or oxygen: metals form oxides. Sodium and potassium form oxides that are basic and dissolve in water, magnesium forms a basic oxide, and aluminium forms an amphoteric oxide.
• With water: potassium and sodium react violently with cold water, calcium reacts with cold water, and magnesium reacts with hot water, each giving a metal hydroxide and hydrogen.
• With dilute acids: metals above hydrogen in the series give hydrogen with dilute acids, for example Zn + 2HCl → ZnCl₂ + H₂.
• Displacement: a more reactive metal displaces a less reactive metal from its salt solution, as in Fe + CuSO₄ → FeSO₄ + Cu, which is the practical the board asks for.
• The reactivity series itself: potassium, sodium, calcium, magnesium, aluminium, zinc, iron, lead, copper, silver, gold, from the most reactive downwards.

A metal and a non-metal form an ionic compound, and the mechanism is a straight transfer of electrons rather than a share. Sodium, with the configuration 2,8,1, has one electron in its outermost shell and loses it to attain the stable configuration 2,8. Chlorine, with the configuration 2,8,7, needs one electron to complete its octet and so gains it.What is left is a sodium ion, Na+, and a chloride ion, Cl-. These two oppositely charged ions attract each other strongly, and the resulting electrostatic force of attraction is the ionic bond. The compound formed is sodium chloride, NaCl, and it is an ionic compound because it is held together by ions and not by shared electrons.

• The metal loses electrons and becomes a cation. Sodium gives its single valence electron and becomes Na+, with the stable configuration 2,8.
• The non-metal gains electrons and becomes an anion. Chlorine gains one electron and becomes Cl-, also with the configuration 2,8.
• The opposite charges attract, and that attraction between the cation and the anion is the ionic bond.
• Sodium chloride is written as Na⁺ and Cl⁻ paired, and the overall formula NaCl is electrically neutral because the two charges balance.
• Magnesium, which loses two electrons to become Mg²⁺, and oxygen, which gains two to become O²⁻, give magnesium oxide, MgO, by the same rule.

The properties of an ionic compound follow directly from the fact that it is a giant lattice of alternating cations and anions held by strong electrostatic forces. To break that lattice requires a great deal of energy, which is why ionic compounds are hard and have high melting points.The same lattice explains the solubility rule and the conducting behaviour, and these two together are the marks students most often lose. In the solid state the ions are fixed in position and cannot move, so the compound does not conduct; once melted or dissolved the ions are free to move and carry charge, so it conducts well.

• Physical state and hardness: ionic compounds are crystalline solids, and they are hard but brittle, because shifting one layer knocks ions of like charge together and the lattice splits.
• Melting point: high, because a great deal of energy is needed to break the strong electrostatic attraction between the ions.
• Solubility: soluble in water, since water molecules are polar and hydrate the ions, but insoluble in kerosene and other non-polar solvents.
• Conducting state: they do not conduct electricity in the solid state, because the ions are fixed, and they do conduct in the molten state and in the aqueous state, because the ions are then free to move.
• Formation: a metal with a non-metal gives an ionic compound, and the general equation 2Na + Cl₂ → 2NaCl holds for the whole family of metal chlorides.

Metallurgy is the whole process of obtaining a pure metal from its ore, and the syllabus asks for it in four steps in this order: the concentration of the ore, the conversion of the concentrated ore to its oxide, the reduction of the oxide to the metal, and the refining of the impure metal. Learn the four names in that sequence, because the order itself earns the first mark.The whole set of questions is best answered with zinc as the running example, since the board uses zinc oxide and zinc sulphide in the questions, and with iron for the blast furnace. Thermite welding, in which aluminium reduces iron oxide, is the third standard example and is frequently asked as a one-mark reaction.

• Concentration of the ore: the ore is crushed and then washed with water, so the lighter gangue is carried away and the heavier mineral particles remain, as with the washing of a bauxite ore.
• Conversion to the oxide: the concentrated ore is heated strongly in a furnace in the presence of excess air, and 2ZnS + 3O₂ → 2ZnO + 2SO₂ is the standard equation.
• Reduction to the metal: the oxide is heated with carbon, or carbon monoxide, or a more reactive metal, and ZnO + C → Zn + CO and Fe₂O₃ + 2Al → Al₂O₃ + 2Fe are the two standard reactions.
• Thermite reaction: iron oxide is reduced by aluminium powder, and the temperature reached is high enough to melt the iron, which is why it is used in railway track welding.
• Refining: the impure metal is purified by the electrolytic or the electrolytic refining method, in which the impure metal is the anode, a thin strip of pure metal is the cathode, and the correct electrolyte is used.

Corrosion is the slow destruction of a metal by its surroundings. Iron rusts in the presence of both air and moisture, and the rust is a hydrated iron(III) oxide, written as Fe₂O₃·xH₂O, together with iron(II) sulphate formed along the way. A reddish brown deposit on an iron nail left in water is the standard observation in the practical.Aluminium is far above iron in the reactivity series and should therefore corrode faster, but it does not, and the explanation is the single most popular question in this section. The moment aluminium is exposed to air it forms a thin, compact and impervious layer of aluminium oxide on its surface, and this layer seals the metal underneath and stops any further reaction.

• Rusting of iron: iron rusts in the presence of air and moisture, and the product is hydrated iron(III) oxide, Fe₂O₃·xH₂O, which is flaky and porous and does not protect the iron below.
• Why aluminium survives: aluminium is more reactive than iron, but its thin, impervious coating of Al₂O₃ seals the surface and prevents further oxidation, which is the classic trap in this section.
• Galvanisation: a layer of zinc is coated over the surface of iron by dipping it in molten zinc, and zinc is more reactive than iron, so it corrodes first and protects the iron even when the coating is scratched.
• Painting, oiling and greasing: a coat of paint, oil or grease keeps air and moisture away from the surface, and this is the cheapest method for a gate or a bridge.
• Alloying, anodising and chrome plating: stainless steel resists rusting because of alloying, anodising forms a thick protective oxide layer on aluminium, and chrome plating coats a metal with a layer of chromium.