Chapter Notes

Metals and Non-metals

Elements can be broadly classified into two main categories based on their properties: metals and non-metals. These properties determine how we use them in our daily lives, from the copper wires that carry electricity to the carbon that forms the basis of life.

PHYSICAL PROPERTIES

Metals

Metals can be identified and grouped based on their distinct physical characteristics.

• Metallic Lustre: In their pure state, metals have a shiny surface. This property is known as metallic lustre.
• Hardness: Metals are generally hard, although the degree of hardness varies from one metal to another.
• Malleability: This is the property that allows metals to be beaten into thin sheets. Gold and silver are the most malleable metals.
• Ductility: This is the ability of metals to be drawn into thin wires. Gold is the most ductile metal; a single gram of gold can be drawn into a wire about 2 km long. Malleability and ductility are the reasons metals can be shaped for various uses.
• Conductors of Heat and Electricity: Metals are excellent conductors of heat and electricity. This is why cooking vessels are made of metal. The best conductors of heat are silver and copper, while lead and mercury are relatively poor conductors. Their ability to conduct electricity is why they are used for electrical wiring.
• High Melting Points: Metals typically have high melting points, which allows them to remain solid even when heated to high temperatures, a useful property for cooking vessels.
• Sonorous: Metals produce a distinct ringing sound when they strike a hard surface. This property is called being sonorous, and it's why bells are made of metals.
• State: At room temperature, all metals are solids, with the exception of mercury, which is a liquid.

Non-metals

Non-metals are fewer in number compared to metals and have contrasting properties.

• Examples include carbon, sulphur, iodine, oxygen, and hydrogen.
• State: Non-metals exist as either solids or gases at room temperature. The only exception is bromine, which is a liquid.

Exceptions to General Physical Properties

While these general properties are useful for classification, there are several important exceptions that show we cannot group elements based on physical properties alone.

• State and Melting Point of Metals: While most metals are hard solids with high melting points, there are exceptions.
  • Mercury is a liquid at room temperature.
  • Alkali metals like lithium, sodium, and potassium are so soft they can be cut with a knife. They also have low densities and low melting points.
  • Gallium and caesium have such low melting points that they will melt if you keep them on your palm.
• Lustre of Non-metals: Although non-metals are typically dull, iodine is a non-metal that is lustrous (shiny).
• Hardness and Conductivity of Non-metals:
  • Carbon is a non-metal that can exist in different forms called allotropes.
  • Diamond, an allotrope of carbon, is the hardest natural substance known and has a very high melting and boiling point.
  • Graphite, another allotrope of carbon, is a good conductor of electricity, which is unusual for a non-metal.

CHEMICAL PROPERTIES OF METALS

The chemical properties of elements provide a clearer basis for classifying them as metals or non-metals. Generally, metals form basic oxides, while non-metals form acidic oxides.

What happens when Metals are burnt in Air?

Almost all metals combine with oxygen to form metal oxides. Metal + Oxygen → Metal oxide

• For example, when copper is heated, it combines with oxygen to form a black substance, copper(II) oxide. $2 \mathrm{Cu}+\mathrm{O}_{2} \rightarrow 2 \mathrm{CuO}$
• Similarly, aluminium forms aluminium oxide. $4 \mathrm{Al}+3 \mathrm{O}_{2} \rightarrow 2 \mathrm{Al}_{2} \mathrm{O}_{3}$

Nature of Metal Oxides Metal oxides are generally basic in nature. Some, like sodium oxide ($Na_2O$) and potassium oxide ($K_2O$), are soluble in water and form alkalis (bases that dissolve in water). $\mathrm{Na}_{2} \mathrm{O}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow 2 \mathrm{NaOH}(\mathrm{aq})$ $\mathrm{K}_{2} \mathrm{O}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow 2 \mathrm{KOH}(\mathrm{aq})$

However, some metal oxides, like aluminium oxide and zinc oxide, exhibit both acidic and basic properties. These are known as amphoteric oxides. They can react with both acids and bases to produce salt and water.

• Reaction with acid: $\mathrm{Al}_{2} \mathrm{O}_{3}+6 \mathrm{HCl} \rightarrow 2 \mathrm{AlCl}_{3}+3 \mathrm{H}_{2} \mathrm{O}$
• Reaction with base: $\mathrm{Al}_{2} \mathrm{O}_{3}+2 \mathrm{NaOH} \rightarrow 2 \mathrm{NaAlO}_{2} \text{ (Sodium aluminate)} +\mathrm{H}_{2} \mathrm{O}$

Reactivity with Oxygen Varies Metals show different levels of reactivity towards oxygen.

• Potassium (K) and Sodium (Na) react so vigorously that they catch fire in open air. To prevent this, they are stored immersed in kerosene oil.
• Magnesium (Mg), Aluminium (Al), Zinc (Zn), and Lead (Pb) form a thin, protective layer of oxide on their surface at room temperature. This layer prevents further oxidation (corrosion).
• Iron (Fe) does not burn on heating, but iron filings burn vigorously when sprinkled in a flame.
• Copper (Cu) does not burn but gets coated with a black layer of copper(II) oxide when heated.
• Silver (Ag) and Gold (Au) do not react with oxygen, even at high temperatures.

What happens when Metals react with Water?

Metals react with water to produce a metal oxide and hydrogen gas. If the metal oxide is soluble in water, it further dissolves to form a metal hydroxide. Metal + Water → Metal oxide + Hydrogen Metal oxide + Water → Metal hydroxide

The reactivity with water also varies greatly among metals.

• Reaction with Cold Water:

  • Potassium and sodium react violently with cold water. The reaction is so exothermic (releases so much heat) that the hydrogen gas produced immediately catches fire. $2 \mathrm{~K}(\mathrm{~s})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow 2 \mathrm{KOH}(\mathrm{aq})+\mathrm{H}_{2}(\mathrm{~g})+\text { heat energy }$ $2 \mathrm{Na}(\mathrm{~s})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow 2 \mathrm{NaOH}(\mathrm{aq})+\mathrm{H}_{2}(\mathrm{~g})+\text { heat energy }$
  • Calcium's reaction is less violent, and the heat produced is not enough to ignite the hydrogen. Calcium starts floating because the bubbles of hydrogen gas stick to its surface. $\mathrm{Ca}(\mathrm{~s})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow \mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq})+\mathrm{H}_{2}(\mathrm{~g})$

• Reaction with Hot Water:

  • Magnesium does not react with cold water but reacts with hot water to form magnesium hydroxide and hydrogen. It also floats due to hydrogen bubbles sticking to its surface.

• Reaction with Steam:

  • Metals like aluminium, iron, and zinc do not react with cold or hot water. They react with steam to form the metal oxide and hydrogen. $2 \mathrm{Al}(\mathrm{~s})+3 \mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \rightarrow \mathrm{Al}_{2} \mathrm{O}_{3}(\mathrm{~s})+3 \mathrm{H}_{2}(\mathrm{~g})$ $3 \mathrm{Fe}(\mathrm{~s})+4 \mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \rightarrow \mathrm{Fe}_{3} \mathrm{O}_{4}(\mathrm{~s})+4 \mathrm{H}_{2}(\mathrm{~g})$

• No Reaction with Water:

  • Metals such as lead, copper, silver, and gold do not react with water at all.

What happens when Metals react with Acids?

Metals generally react with dilute acids to produce a salt and hydrogen gas. Metal + Dilute acid → Salt + Hydrogen

The vigor of the reaction depends on the metal's reactivity.

• The rate of bubble formation (hydrogen gas) indicates the speed of the reaction. The reactivity order with dilute hydrochloric acid is: Mg > Al > Zn > Fe.
• In the case of copper, no bubbles are seen, indicating it does not react with dilute HCl.

How do Metals react with Solutions of other Metal Salts?

A more reactive metal can displace a less reactive metal from its compound in a solution or molten form. This is known as a displacement reaction.

Metal A + Salt solution of B → Salt solution of A + Metal B

This principle provides excellent evidence for the relative reactivities of metals. If metal A displaces metal B, then metal A is more reactive than metal B.

The Reactivity Series

The reactivity series is a list of metals arranged in the order of their decreasing chemical activity. It helps predict the outcomes of displacement reactions.

How do Metals and Non-metals React?

The reactions between metals and non-metals are governed by their tendency to achieve a stable electron configuration, like that of a noble gas (a full outer electron shell).

• Metals have 1, 2, or 3 electrons in their outermost shell. They tend to lose these valence electrons to form positively charged ions, called cations.
• Non-metals typically have 4, 5, 6, or 7 electrons in their outermost shell. They tend to gain electrons to complete their outer shell, forming negatively charged ions, called anions.

The compounds formed by the transfer of electrons from a metal to a non-metal are known as ionic compounds or electrovalent compounds. These compounds are held together by strong electrostatic forces of attraction between the oppositely charged ions.