Lesson 7: Metals and Nonmetals

In the figure : In the figure elements are metals, nonmetals or metalloids. Fe, Cu and Al are metals, C, S and P are nonmetals, and Si, As and Ge are metalloids.

Rule 1: Three groups of elements — Gold, silver, iron, copper, aluminium, magnesium, calcium, sodium and platinum are metals. Carbon, sulphur and phosphorus are nonmetals. Silicon, arsenic and germanium are metalloids.

• Easy : Copper wire is a metal; coal (carbon) is a nonmetal.
• Medium : Silicon is a metalloid, between a metal and a nonmetal.
• Exam-type : Mercury and gallium are metals that are liquid or melt near room temperature.

In the figure : In the figure metals shine (lustre), can be drawn into wires (ductility), can be hammered into sheets (malleability) and ring when struck (sonority).

Rule 2: Physical properties — State: solid, except mercury and gallium (liquid at room temperature). Lustre: shine on a cleaned or freshly cut surface. Hardness: generally hard; sodium and potassium are soft and can be cut with a knife. Ductility: can be drawn into wires. Malleability: can be hammered into thin sheets. Sonority: ring when struck, like a school bell.

• Easy : A copper wire shows ductility.
• Medium : Aluminium foil shows malleability.
• Exam-type : Gold is so malleable that it can be made into a sheet 1/10,000 mm thick, so 1 mm of gold could be spread into 10,000 such layers.

In the figure : In the figure of density in g per cm³, lithium, potassium and sodium are lighter than water (below 1) and the other metals shown are heavier.

Rule 3: Density and conduction — Metals are good conductors of heat (silver, copper and aluminium are the best) and of electricity; lead is an exception. Density is high, except sodium, potassium and lithium, which are lighter than water (lithium 0.53 g/cc). Melting and boiling points are generally high (exceptions: Hg, Ga, Na, K).

• Easy : Lithium (0.53 g/cc) floats on water because it is lighter than water (1 g/cc).
• Medium : 100 cm³ of lithium has mass 100 × 0.53 = 53 g.
• Exam-type : Copper is used for electric wires and aluminium for utensils and foils, because they are good conductors.

In the figure : In the figure metals such as copper conduct electricity, so the bulb glows. Graphite is the one nonmetal that conducts, while plastic and sulphur do not.

Rule 4: Testing conduction — Join a cell, a bulb and the sample in a circuit. If the bulb glows, the sample conducts. Copper conducts. Graphite, the one nonmetal that conducts, also conducts. Plastic and sulphur do not.

• Easy : If the bulb glows, the material conducts electricity.
• Medium : Use only a cell for such a test; never test with mains electricity.
• Exam-type : A school bell is made of metal as it is sonorous.

Spot the difference

In the figure : In the figure nonmetals occur as solids (C, S, P), a liquid (bromine, Br₂) and gases (H₂, N₂, O₂).

Rule 1: Nonmetals — Carbon, sulphur and phosphorus are solids, bromine (Br₂) is a liquid, and H₂, N₂ and O₂ are gases. Generally non-lustrous (exceptions: diamond and iodine crystals shine). Bad conductors of heat and electricity. Low density and generally low melting and boiling points (carbon and boron melt at high temperatures).

• Easy : Oxygen and nitrogen are gases at room temperature.
• Medium : Bromine is the only nonmetal that is liquid at room temperature.
• Exam-type : Sulphur is yellow, brittle and does not conduct electricity.

In the figure : In the figure a metal flattens into a sheet on hammering (malleable), but solid nonmetals such as coal are brittle and break into pieces.

Rule 2: Brittle versus malleable — Solid nonmetals are brittle: coal breaks on hammering. They are neither ductile nor malleable.

• Easy : Coal breaks on hammering.
• Medium : An iron nail flattens a little on hammering, but a piece of sulphur powders.
• Exam-type : Wires are made of metals and not of nonmetals, because nonmetals cannot be drawn into wires.

In the figure : In the figure diamond and graphite are both forms (allotropes) of carbon. Diamond is the hardest natural substance and graphite conducts electricity.

Rule 3: Allotropes and metalloids — Diamond and graphite are allotropes of carbon. Diamond is the hardest natural substance; graphite is a very good conductor of electricity. Metalloids (arsenic, silicon, germanium, antimony) have properties between those of metals and nonmetals.

• Easy : Diamond is hard; graphite is soft and slippery.
• Medium : Pencil lead is graphite, not lead.
• Exam-type : Silicon, a metalloid, is used in computer chips because it is a semiconductor.

Spot the difference

In the figure : In the figure metals lose the electrons of the outermost shell and form positive ions (cations): Na⁺, Mg²⁺ and Al³⁺.

Rule 1: Metals lose electrons — Most metals have up to three electrons in the outermost shell (Na 2, 8, 1; Mg 2, 8, 2; Al 2, 8, 3). They lose them to form cations: Na → Na⁺ + e⁻; Mg → Mg²⁺ + 2e⁻; Al → Al³⁺ + 3e⁻.

• Easy : Sodium loses 1 electron and becomes Na⁺.
• Medium : Calcium (2, 8, 8, 2) loses 2 electrons and becomes Ca²⁺.
• Exam-type : After losing 3 electrons, Al has 13 − 3 = 10 electrons and 13 protons, so the charge is 13 − 10 = +3.

In the figure : In the figure zinc and dilute hydrochloric acid give hydrogen gas (A zinc, B bubbles). The gas burns with a pop near a burning splinter (C).

Rule 2: Reactions of metals — Metal + oxygen → metal oxide (basic). Metal oxide + acid → salt + water. Metal + dilute acid → salt + hydrogen gas (zinc with dilute HCl: Zn + 2HCl → ZnCl₂ + H₂). Sodium and potassium react with cold water to give hydroxides and hydrogen; magnesium needs steam.

• Easy : Zinc with dilute HCl gives hydrogen gas bubbles.
• Medium : Balanced: Mg + 2HCl → MgCl₂ + H₂ has Mg 1, H 2, Cl 2 on both sides.
• Exam-type : Sodium reacts violently with water, so it is handled only by the teacher with great care and never touched.

Spot the difference

In the figure : In the figure nonmetals gain electrons to fill the outermost shell and form negative ions (anions): Cl⁻, O²⁻ and N³⁻.

Rule 1: Nonmetals gain electrons — Most nonmetals have 4 to 7 electrons in the valence shell (N 2, 5; O 2, 6; Cl 2, 8, 7). They gain electrons to form anions: Cl + e⁻ → Cl⁻; O + 2e⁻ → O²⁻; N + 3e⁻ → N³⁻.

• Easy : Chlorine (2, 8, 7) gains 1 electron and becomes Cl⁻ (2, 8, 8).
• Medium : Oxygen (2, 6) gains 2 electrons to reach 2, 8.
• Exam-type : Fluorine (2, 7) needs 8 − 7 = 1 electron, so its ion is F⁻.

In the figure : In the figure oxides of metals are basic (turn red litmus blue) and oxides of nonmetals are acidic (turn blue litmus red).

Rule 2: Oxides of nonmetals — Nonmetal + oxygen → nonmetal oxide (acidic): C + O₂ → CO₂. Nonmetal oxides react with bases to give salt and water (CO₂ + 2NaOH → Na₂CO₃ + H₂O). They react with water to form acids: CO₂ gives H₂CO₃, SO₂ gives H₂SO₃ and SO₃ gives H₂SO₄. Nonmetals do not react with dilute acids.

• Easy : CO₂ in water makes carbonic acid; this is the fizz in a soda bottle.
• Medium : Balanced: CO₂ + 2NaOH → Na₂CO₃ + H₂O has Na 2, C 1, O 4, H 2 on both sides.
• Exam-type : Sulphur burning makes SO₂; with water it gives sulphurous acid (H₂SO₃), a reason for acid rain from industrial smoke.

Spot the difference

In the figure : In the figure carat shows the parts of pure gold out of 24. 22 carat gold has 22 parts gold and 2 parts copper or silver (91.66 percent pure).

Rule 1: Noble metals and carat — Gold, silver, platinum, palladium and rhodium occur in the elemental state and do not react readily. 100% pure gold is 24 carat, but it is soft, so goldsmiths mix copper or silver. Ornaments use 22 carat gold (91.66%); 18 carat is 75% and 14 carat is 58.33%. Uses: ornaments, medals, silver in medicines (antibacterial), electronic devices, platinum and palladium as catalysts.

• Easy : 24 carat is 24 ÷ 24 × 100 = 100 percent gold.
• Medium : 18 carat is 18 ÷ 24 × 100 = 75 percent gold.
• Exam-type : A 12 g chain of 22 carat gold contains 12 × 22 ÷ 24 = 11 g of pure gold, and 1 g of other metal.

In the figure : In the figure of corrosion, iron gets a reddish layer (rust), copper a green layer and silver a black layer. Oil, paint and plating prevent it.

Rule 2: Corrosion and alloys — Corrosion: gases in the air react with metals in the presence of moisture. Iron gets a reddish deposit (rust), copper a green one (copper carbonate, as on the Statue of Liberty) and silver a black one. Prevention: oil, grease, varnish, paint and plating (for example zinc plating on iron). Alloys: stainless steel (iron with carbon, chromium and nickel) and bronze (copper and tin). The Delhi iron pillar, about 1500 years old, is still lustrous because it is made of an alloy.

• Easy : Rust is a reddish layer on iron.
• Medium : Painting an iron gate keeps air and moisture away and prevents rust.
• Exam-type : The Delhi iron pillar is about 1500 years old, so it has stood for 1500 ÷ 100 = 15 centuries.

Spot the difference