Physical Properties Of Metals And Non-metals

Materials found around us, like iron, aluminium, and copper, can be broadly classified based on their characteristics. Some materials are identified as metals, while others are categorised as non-metals. These classifications are primarily based on their physical and chemical properties. Key physical properties include appearance (like lustre) and hardness.

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Appearance and Hardness

Metals typically have a shiny surface, which is referred to as lustre. They are also generally hard materials. Non-metals, in contrast, are often dull in appearance and are usually not very hard.

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Malleability

When materials like iron or aluminium wire are beaten with a hammer, their shape changes; they can be flattened into thin sheets. This property, by which a material can be hammered or beaten into thin sheets, is called malleability. Malleability is a characteristic property of metals. Materials like coal or pencil lead, when hammered, tend to break into powdery pieces instead of flattening, showing they are not malleable.

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Ductility

Another important property of metals is ductility. This is the ability of a material to be drawn or stretched into thin wires. Metals like aluminium and copper are commonly used to make wires because of this property. Non-metals, such as coal, cannot be drawn into wires.

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Sonority

When metals are struck, they typically produce a ringing sound. Materials that produce a ringing sound when struck hard are said to be sonorous. This property is characteristic of metals. Non-metals do not produce such ringing sounds; they are not sonorous.

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Conductivity

Materials differ in their ability to conduct heat and electricity.

• Heat Conductivity: Metals are generally good conductors of heat, meaning heat passes through them easily. This is why metal pans are used for cooking, although their handles are often made of poor heat conductors like plastic or wood to prevent burns.
• Electrical Conductivity: Metals are also good conductors of electricity, allowing electric current to flow through them. This property makes metals like copper and aluminium ideal for making electrical wires. Non-metals, on the other hand, are generally poor conductors (insulators) of heat and electricity.

Based on these physical properties, we can summarise that metals are typically hard, lustrous, malleable, ductile, sonorous, and good conductors of heat and electricity. Examples include iron, copper, aluminium, calcium, and magnesium.

In contrast, non-metals are usually soft, dull in appearance, break easily (not malleable or ductile), are not sonorous, and are poor conductors of heat and electricity. Examples include sulphur, carbon, oxygen, and phosphorus.

There are some exceptions to these general properties. For example, sodium and potassium are metals but are soft enough to be cut with a knife. Mercury is the only metal that exists in a liquid state at room temperature.

Chemical Properties Of Metals And Non-metals

Metals and non-metals exhibit different behaviours when they react with other substances like oxygen, water, acids, and bases.

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Reaction With Oxygen

When metals react with oxygen, they form metal oxides. These metal oxides are generally basic in nature.

• Iron: Iron reacts with oxygen in the presence of water to form rust (iron oxide). The reaction is: $\text{Fe} + \text{O}_2 + \text{H}_2\text{O} \rightarrow \text{Rust}$ (mainly hydrated iron(III) oxide). Rust turns red litmus paper blue, indicating its basic nature.
• Magnesium: When magnesium ribbon burns in air (reacts with oxygen), it forms magnesium oxide. The reaction is: $\text{Mg} + \text{O}_2 \rightarrow \text{MgO}$. Dissolving magnesium oxide in water and testing with litmus paper shows that it is also basic, turning red litmus blue.
• Copper: When a copper vessel is exposed to moist air, it develops a dull green coating, which is a mixture of copper hydroxide ($\text{Cu(OH)}_2$) and copper carbonate ($\text{CuCO}_3$). This is also an oxidation reaction.

When non-metals react with oxygen, they form non-metal oxides. These non-metal oxides are generally acidic in nature.

• Sulphur: When sulphur is burned in air (reacts with oxygen), it produces sulphur dioxide gas ($\text{SO}_2$). The reaction is: $\text{S} + \text{O}_2 \rightarrow \text{SO}_2$. When sulphur dioxide is dissolved in water, it forms sulphurous acid ($\text{H}_2\text{SO}_3$). The reaction is: $\text{SO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_3$. Sulphurous acid turns blue litmus paper red, confirming its acidic nature.

The oxides formed by metals are basic, while the oxides formed by non-metals are acidic.

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Reaction With Water

Metals vary in their reactivity with water.

• Sodium: Sodium is a very reactive metal. It reacts vigorously with water, producing heat and hydrogen gas. Due to its high reactivity with air and water, sodium is stored in kerosene to prevent contact.
• Iron: Iron reacts with water very slowly, primarily with steam.

Generally, non-metals do not react with water. However, some non-metals can be very reactive in air. To protect them from reacting with atmospheric oxygen, they are stored in water. For example, phosphorus is a highly reactive non-metal that catches fire when exposed to air; hence, it is stored in water.

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Reactions With Acids

Metals generally react with dilute acids (like dilute hydrochloric acid or dilute sulphuric acid) to produce a metal salt and hydrogen gas ($\text{H}_2$). Hydrogen gas is flammable and burns with a 'pop' sound when a burning matchstick is brought near it.

For example, magnesium reacts with dilute hydrochloric acid: $\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2\uparrow$.

Non-metals generally do not react with dilute acids. While most metals react with dilute acids, some, like copper, may not react with dilute hydrochloric acid even when heated, but might react with other acids like concentrated sulphuric acid.

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Reactions With Bases

Some metals react with bases (like sodium hydroxide solution) to produce hydrogen gas. For example, aluminium reacts with sodium hydroxide solution to produce hydrogen gas.

Reactions of non-metals with bases are typically more complex and less common.

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Displacement Reactions

A more reactive metal can displace a less reactive metal from its compound (salt solution). This means that if a more reactive metal is placed in a solution containing the salt of a less reactive metal, the more reactive metal will take the place of the less reactive metal in the compound, and the less reactive metal will be set free.

For example, zinc ($\text{Zn}$) is more reactive than copper ($\text{Cu}$). When zinc granules are added to a copper sulphate solution ($\text{CuSO}_4$, which is blue), zinc displaces copper. The blue colour of copper sulphate disappears, and red-brown copper is deposited. The reaction is: $\text{CuSO}_4 \text{(aq, Blue)} + \text{Zn (s)} \rightarrow \text{ZnSO}_4 \text{(aq, Colourless)} + \text{Cu (s, Red)}$.

Similarly, iron ($\text{Fe}$) is more reactive than copper. When an iron nail is placed in copper sulphate solution, iron displaces copper: $\text{CuSO}_4 \text{(aq, Blue)} + \text{Fe (s)} \rightarrow \text{FeSO}_4 \text{(aq, Light green)} + \text{Cu (s, Red)}$.

However, a less reactive metal cannot displace a more reactive metal from its salt solution. For instance, if copper turnings are placed in zinc sulphate solution ($\text{ZnSO}_4$) or iron sulphate solution ($\text{FeSO}_4$), no reaction occurs because copper is less reactive than both zinc and iron. Similarly, iron cannot displace zinc from zinc sulphate solution because iron is less reactive than zinc.

Based on these displacement reactions, the relative reactivity of zinc, iron, and copper can be determined:

Reactivity Order: Zinc > Iron > Copper

An element is a pure substance that cannot be broken down further into simpler substances by chemical reactions, cooling, heating, or electrolysis. Examples include sulphur, iron, and carbon. The smallest unit of an element is an atom. A sample of an element contains only one type of atom. There are a limited number of naturally occurring elements (around 94). Elements are broadly classified into metals, non-metals, and metalloids. Metalloids possess properties intermediate between those of metals and non-metals.

Uses Of Metals And Non-metals

Metals and non-metals have countless applications in our daily lives due to their diverse properties.

Uses of Metals: Due to their properties like strength, hardness, malleability, ductility, and conductivity, metals are used extensively for:

• Making machinery and industrial gadgets.
• Building automobiles, aeroplanes, trains, and satellites.
• Manufacturing cooking utensils and water boilers.
• Electrical wiring (copper, aluminium).
• Jewellery (gold, silver).
• Thermometers (mercury).

Uses of Non-metals: Non-metals are also indispensable, serving various vital functions and applications:

• Oxygen: Essential non-metal for breathing by all living organisms.
• Nitrogen and Phosphorus: Used in fertilisers to improve plant growth.
• Chlorine: Used in water purification processes to kill microbes.
• Iodine: Used in a purple-coloured solution (tincture of iodine) as an antiseptic applied on wounds.
• Sulphur and Phosphorus: Used in crackers and fireworks.

Many other uses exist for both metals and non-metals based on their specific physical and chemical characteristics.

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