Comprehensive Notes on Metals and Non-metals
Introduction
- Elements are classified as metals or non-metals based on their properties.
- Metals and non-metals have various uses in daily life.
- Metals in their pure state have a shining surface called metallic lustre.
- Example metals used: iron, copper, aluminium, magnesium.
Activity 3.2: Malleability
- Some metals can be beaten into thin sheets; this property is called malleability.
- Gold and silver are the most malleable metals.
Activity 3.3: Hardness
- Metals are generally hard, but hardness varies.
- Metals used: iron, zinc, lead, copper.
Activity 3.4: Ductility
- The ability of metals to be drawn into thin wires is called ductility.
- Gold is the most ductile metal; 1 gram can be drawn into a 2 km long wire.
- Metals can be shaped according to needs due to malleability and ductility.
Activity 3.5: Conductivity of Heat
- Metals are good conductors of heat and have high melting points.
- Silver and copper are the best conductors; lead and mercury are poor conductors.
Conductivity of Electricity
- Electric wires are coated with polyvinylchloride (PVC) or a rubber-like material.
- Metals produce a sound when struck, called sonorous.
- School bells are made of metals due to their sonorous property.
- Non-metals can be solids or gases, except bromine, which is a liquid.
- Non-metals do not typically share the same physical properties as metals.
Activity 3.6: Electric Circuit
- Testing conductivity by placing a material in a circuit between terminals A and B.
- If the bulb glows, the material conducts electricity.
Activity 3.7
- Non-metal samples: carbon (coal or graphite), sulphur, and iodine.
- Observations are compiled in a table to compare metals and non-metals focusing on hardness, malleability, ductility, conductivity, and sonority.
Exceptions in Physical Properties
- Elements cannot be grouped solely based on physical properties; there are exceptions.
- All metals are solid at room temperature except mercury.
- Gallium and caesium have very low melting points.
- Iodine is a lustrous non-metal.
- Carbon exists in different allotropes (diamond and graphite).
- Diamond is the hardest natural substance with a high melting and boiling point.
- Graphite is a conductor of electricity.
- Alkali metals (lithium, sodium, potassium) are soft and can be cut with a knife; they also have low densities and melting points.
Activity 3.8
- Magnesium ribbon and sulphur powder are burned to test acidic or basic properties.
- Burning magnesium produces a basic product.
- Burning sulphur produces an acidic product.
Question Examples
- Example of a metal liquid at room temperature: mercury.
- Metal easily cut with a knife: sodium.
- Best conductor of heat: silver or copper.
- Poor conductor of heat: lead.
- Malleable: Ability to be beaten into thin sheets.
- Ductile: Ability to be drawn into thin wires.
Reactions with Air
Activity 3.9
- Metals burn in air to form metal oxides: Metal + Oxygen \rightarrow Metal \space oxide
- Copper heated in air forms copper(II) oxide: 2Cu + O_2 \rightarrow 2CuO
- Aluminium forms aluminium oxide: 4Al + 3O2 \rightarrow 2Al2O_3
- Metal oxides are generally basic.
- Amphoteric oxides (e.g., aluminium oxide, zinc oxide) react with both acids and bases:
- Al2O3 + 6HCl \rightarrow 2AlCl3 + 3H2O
- Al2O3 + 2NaOH \rightarrow 2NaAlO2 + H2O
- Sodium oxide and potassium oxide dissolve in water to form alkalis:
- Na2O(s) + H2O(l) \rightarrow 2NaOH(aq)
- K2O(s) + H2O(l) \rightarrow 2KOH(aq)
Reactivity with Oxygen
- Different metals show different reactivities towards oxygen.
- Potassium and sodium react vigorously and are stored in kerosene oil.
- Magnesium, aluminium, zinc, and lead form a protective oxide layer preventing further oxidation.
- Iron filings burn vigorously when sprinkled in a flame.
- Copper is coated with a black layer of copper(II) oxide when heated.
- Silver and gold do not react with oxygen even at high temperatures.
Anodising
- Anodising is forming a thick oxide layer of aluminium for corrosion resistance using dilute sulphuric acid during electrolysis.
Reactions with Water
Activity 3.10
- Metals react with water to produce metal oxide and hydrogen gas: Metal + Water \rightarrow Metal \space oxide + Hydrogen
- Metal oxides soluble in water form metal hydroxides: Metal \space oxide + Water \rightarrow Metal \space hydroxide
- Potassium and sodium react violently with cold water:
- 2K(s) + 2H2O(l) \rightarrow 2KOH(aq) + H2(g) + heat \space energy
- 2Na(s) + 2H2O(l) \rightarrow 2NaOH(aq) + H2(g) + heat \space energy
- Calcium reacts less violently:
- Ca(s) + 2H2O(l) \rightarrow Ca(OH)2(aq) + H_2(g)
- Magnesium reacts with hot water to form magnesium hydroxide and hydrogen.
- Aluminium, iron, and zinc react with steam:
- 2Al(s) + 3H2O(g) \rightarrow Al2O3(s) + 3H2(g)
- 3Fe(s) + 4H2O(g) \rightarrow Fe3O4(s) + 4H2(g)
- Lead, copper, silver, and gold do not react with water.
Reactions with Acids
- Metals react with dilute acids to give salt and hydrogen gas: Metal + Dilute \space acid \rightarrow Salt + Hydrogen
Activity 3.11
- Testing reaction rates with hydrochloric acid. Magnesium reacts fastest.
- Nitric acid ((HNO3)) is a strong oxidising agent and oxidises (H2) to water, reducing itself to nitrogen oxides.
- Magnesium ((Mg)) and manganese ((Mn)) react with very dilute (HNO3) to evolve (H2) gas.
Aqua Regia
- Aqua regia is a mixture of concentrated hydrochloric acid and concentrated nitric acid in a 3:1 ratio that can dissolve gold and platinum.
Activity 3.12
- Reactive metals displace less reactive metals from their compounds in solution.
- Metal \space A + Salt \space solution \space of \space B \rightarrow Salt \space solution \space of \space A + Metal \space B
Reactivity Series
- The reactivity series is a list of metals arranged in order of their decreasing activities.
| Metal | Symbol | Reactivity |
|---|
| Potassium | K | Most reactive |
| Sodium | Na | |
| Calcium | Ca | |
| Magnesium | Mg | |
| Aluminium | Al | |
| Zinc | Zn | |
| Iron | Fe | |
| Lead | Pb | |
| Hydrogen | H | |
| Copper | Cu | |
| Mercury | Hg | |
| Silver | Ag | |
| Gold | Au | Least reactive |
- Noble gases have completely filled valence shells and show little chemical activity.
- Elements react to attain a completely filled valence shell.
- Sodium atom loses an electron to form (Na^+) cation.
- Chlorine gains an electron to form (Cl^-) anion.
- Sodium chloride ((NaCl)) is formed by electrostatic attraction between (Na^+) and (Cl^-) ions.
- Magnesium chloride ((MgCl_2)) is another ionic compound formed by electron transfer.
Properties of Ionic Compounds
Activity 3.13
- Ionic compounds are solids with strong inter-ionic forces.
- They have high melting and boiling points.
- Generally soluble in water and insoluble in solvents like kerosene and petrol.
- Conduct electricity in solution or molten state but not in solid-state.
| Ionic Compound | Melting Point (K) | Boiling Point (K) |
|---|
| (NaCl) | 1074 | 1686 |
| (LiCl) | 887 | 1600 |
| (CaCl_2) | 1045 | 1900 |
| (CaO) | 2850 | 3120 |
| (MgCl_2) | 981 | 1685 |
- The earth’s crust is the major source of metals.
- Minerals are elements or compounds in the earth’s crust.
- Ores are minerals with a high percentage of a particular metal.
- Metals at the bottom of the activity series are found in a free state (e.g., gold, silver, platinum).
- Metals at the top of the series are highly reactive and found as compounds.
- Metals in the middle are moderately reactive and found as oxides, sulphides, or carbonates.
Enrichment of Ores
- Ores are contaminated with impurities like soil and sand, called gangue.
- Gangue is removed based on physical or chemical properties.
- Oxides of these metals are reduced by heating alone.
- Cinnabar ((HgS)) is heated in air to form mercuric oxide ((HgO)), then reduced to mercury.
- 2HgS(s) + 3O2(g) \rightarrow 2HgO(s) + 2SO2(g)
- 2HgO(s) \rightarrow 2Hg(l) + O_2(g)
- (Cu_2S) is heated in air to obtain copper.
- 2Cu2S + 3O2(g) \rightarrow 2Cu2O(s) + 2SO2(g)
- 2Cu2O + Cu2S \rightarrow 6Cu(s) + SO_2(g)
- These metals are present as sulphides or carbonates.
- Sulphides are converted to oxides by roasting (heating in excess air).
- Carbonates are converted to oxides by calcination (heating in limited air).
Roasting and Calcination Examples
- Roasting: 2ZnS(s) + 3O2(g) \rightarrow 2ZnO(s) + 2SO2(g)
- Calcination: ZnCO3(s) \rightarrow ZnO(s) + CO2(g)
- Metal oxides are reduced using reducing agents like carbon: ZnO(s) + C(s) \rightarrow Zn(s) + CO(g)
Displacement Reactions
- Highly reactive metals (Na, Ca, Al) displace less reactive metals.
- Thermit reaction: Fe2O3(s) + 2Al(s) \rightarrow 2Fe(l) + Al2O3(s) + Heat
- These metals are obtained by electrolytic reduction.
- Sodium, magnesium, and calcium are obtained by electrolysis of their molten chlorides.
- At cathode: Na^+ + e^- \rightarrow Na
- At anode: 2Cl^- \rightarrow Cl_2 + 2e^-
- Aluminium is obtained by electrolytic reduction of aluminium oxide.
- Electrolytic refining is widely used for metals like copper, zinc, tin, nickel, silver, and gold.
- Impure metal is the anode, pure metal is the cathode.
- Metal salt solution is the electrolyte.
- Pure metal from the anode dissolves and deposits on the cathode.
- Insoluble impurities settle as anode mud.
Corrosion
- Silver articles become black due to reaction with sulphur: Ag + S \rightarrow Ag_2S
- Copper reacts with moist (CO2) to form basic copper carbonate: Cu + CO2 + H2O \rightarrow CuCO3 "." Cu(OH)_2
- Iron rusts when exposed to moist air.
Activity 3.14
- Investigating conditions for iron rusting.
- Tube A: Iron nails rust due to air and water.
- Tube B: No rust due to oil preventing air dissolving in water.
- Tube C: No rust due to anhydrous calcium chloride absorbing moisture.
Prevention of Corrosion
- Methods include painting, oiling, greasing, galvanising, chrome plating, anodising, or making alloys.
- Galvanisation: Coating with zinc.
Alloys
- Alloys are homogeneous mixtures of two or more metals or a metal and a non-metal.
- Examples: brass (copper and zinc), bronze (copper and tin), solder (lead and tin).