Class 8 Science Chapter 4 Materials: Metals and Non- Metals Notes Important for all Competitive Examinations

Introduction

Metals are typically good conductors of heat and electricity, have a metallic luster, and are generally denser and harder than non-metals. Non-metals, on the other hand, are generally poor conductors of heat and electricity, do not have a metallic luster, and are generally less dense and softer than metals.

Physical Properties of Metals and Non-metals

• When an iron object is beaten, it becomes more malleable and can be shaped into a new form. The iron becomes softer and easier to work with as the internal structure of the metal is changed through the process of hammering or forging.
• However, if you try to beat a piece of coal, you would not expect to see a similar change in shape. Coal is a non-metal and is much softer and more brittle than iron, so it is not capable of being shaped or formed through hammering or forging. Instead, it would likely break or crumble under the force of the hammer.
• Malleability is the property of metals that allows them to be deformed and reshaped through the process of pounding or rolling, without breaking or cracking. This characteristic is important in many industries because it allows metals to be molded and shaped into a wide range of products, including jewelry, automotive parts, and building materials. Metals that are highly malleable, such as gold, silver, copper, and aluminum, can be easily pounded or rolled into thin sheets. Other metals, such as steel and iron, are less malleable and require more force to be reshaped. Malleability is often used in conjunction with another important property of metals known as ductility, which refers to a metal's ability to be stretched or drawn into thin wires. This property is not exhibited by non-metals such as coal and pencil lead.
• It is generally not recommended to hold a hot metallic pan without a plastic or wooden handle because metals are good conductors of heat. This means that they are able to transfer heat easily from the pan to your hand, which could result in burns. In contrast, wood and plastic are poor conductors of heat, which means they do not transfer heat as easily. This is why they are often used as handles for hot objects - they provide insulation and protect your hand from being burned.
• Electricians often use screwdrivers with plastic or rubber handles because these materials also provide insulation and protect against the risk of electric shock. Metal handles would not provide this protection and could potentially conduct electricity, which could be dangerous.
• Iron, nails, and copper wire are good conductors of heat and electricity, while rolled sulfur and coal are poor conductors.
• Aluminum and copper wires are commonly used in electrical wiring and in other applications where a conductive material is needed.
• Coal is not used as a wire because it is a non-metal and a poor conductor of heat and electricity.
• Ductility is the property of metals that allows them to be drawn into wires.
• When dropped on the floor, an iron sheet or plate, a metal coin, and a piece of coal will produce different sounds. The metal objects will produce a higher-pitched ringing sound, while the coal will produce a duller, lower-pitched sound. This is because the density and stiffness of the materials are different, leading to different vibrations and sounds when they are struck.
• Wooden bells are sometimes used in temples because they produce a deep, mellow sound when struck.
• Metal objects will produce a ringing sound when struck, while wooden objects will produce a duller sound.
• It is possible to determine whether a box is made of metal by striking it and listening for a ringing sound. Metal boxes will produce a ringing sound, while wooden boxes will not.
• Metals are considered to be sonorous materials because they produce a ringing sound when struck. Non-metals are not sonorous.
• Materials that are hard, lustrous, malleable, ductile, sonorous, and good conductors of heat and electricity are generally classified as metals. Examples of metals include iron, copper, aluminum, calcium, and magnesium.
• Materials that are soft, dull in appearance, prone to breaking down into a powdery mass when struck, not sonorous, and poor conductors of heat and electricity are generally classified as non-metals. Examples of non-metals include sulfur, carbon, oxygen, and phosphorus.
• Some metals, such as sodium and potassium, are relatively soft and can be cut with a knife.
• Mercury is the only metal that is liquid at room temperature, making it unique among the elements in the periodic table. Other metals, such as aluminum, copper, and gold, are solid at room temperature and must be heated to high temperatures in order to melt and become a liquid. Mercury's low melting point of -39°C (-38°F) and its ability to remain liquid at room temperature make it useful in a variety of applications, such as thermometers, switches, and fluorescent lamps. Despite its useful properties, mercury is also a toxic substance that can be harmful to humans and the environment if not handled properly.
• These exceptions demonstrate that not all metals exhibit the same characteristics and that there can be variations within the group of metals.

Chemical Properties of Metals and Non-metals

Reaction with Oxygen

Iron (Fe) reacts with oxygen and water to form iron oxide, also known as rust. The chemical reaction can be written as:

2Fe + O2 + H2O -> Fe2O3 + H2

In the presence of moisture, iron oxide forms on the surface of iron or steel objects through a process called corrosion. Rust is a reddish-brown substance that can weaken and damage iron and steel structures over time.

Magnesium (Mg) reacts with oxygen to form magnesium oxide, a white solid that is highly resistant to heat and flames. The chemical reaction can be written as:

2Mg + O2 -> 2MgO

When magnesium is burned, it reacts with oxygen in the air to produce bright white light. This reaction is used in flares and fireworks to produce a bright, long-lasting light. Magnesium oxide is also used in various industrial and medicinal applications.

Copper does not rust like iron does, but it can tarnish and develop a greenish deposit on its surface.

When copper is exposed to moist air for an extended period of time, it can acquire a dull green coating due to the formation of copper hydroxide (Cu(OH)2) and copper carbonate (CuCO3). These compounds are formed through a chemical reaction between copper, water, carbon dioxide, and oxygen.

The reaction can be written as:

2Cu + H2O + CO2 + O2 -> Cu(OH)2 + CuCO3

This reaction occurs in moist air, and the green coating that forms on the surface of the copper is known as a patina. Copper patinas can range in color from light green to blue-green, and they can be polished off if desired. Copper is a relatively corrosion-resistant metal, but it is not immune to tarnish and corrosion, so it is important to take proper care of copper objects to ensure that they remain in good condition.

When a magnesium ribbon is burned, the ash obtained after burning is a basic substance. This can be ascertained by performing a litmus test on the solution obtained by dissolving the ash in water. If the red litmus paper turns blue when dipped in the solution, it indicates that the solution is basic.

In general, metallic oxides are basic in nature, so it is not surprising that the oxide of magnesium, which is produced when magnesium burns, is also basic.

On the other hand, when non-metals react with oxygen, they typically form acidic compounds. For example, sulfur dioxide (SO2), which is produced when sulfur burns in the presence of oxygen, is a highly acidic gas that can cause respiratory problems when inhaled. Similarly, carbon dioxide (CO2), which is produced when carbon-based fuels burn in the presence of oxygen, is a weak acid that can contribute to the acidification of the environment.

Sulphur dioxide is a chemical compound that is formed when Sulphur and oxygen react with each other. It is a toxic gas with a strong, choking odor, and is commonly used as a disinfectant and bleaching agent.

When sulphur dioxide is dissolved in water, it forms a compound called sulphurous acid. This compound is also known as hydrogen sulfite, and is a weak acid that is commonly used as a bleaching agent and disinfectant.

The chemical equation for the reaction between sulphur dioxide and water is: SO2 + H2O → H2SO3. This reaction is exothermic, meaning it releases heat.

Sulphur dioxide is produced through the burning of fossil fuels, such as coal and oil, and is a major contributor to air pollution. It is also released during volcanic eruptions.

Inhaling high levels of sulphur dioxide can be harmful to human health, as it can irritate the respiratory system and cause coughing, wheezing, and shortness of breath. It can also have adverse effects on plants and animals.

Sulphurous acid is a weak acid that is commonly used as a bleaching agent and disinfectant. It is also known as hydrogen sulfite.

One characteristic of sulphurous acid is that it turns blue litmus paper red. This is due to the fact that it is an acid, and litmus paper is designed to change color in the presence of acids.

In general, non-metals tend to form acidic oxides, while metals tend to form basic oxides. However, there are some exceptions to this rule. For example, carbon forms both acidic (carbon dioxide) and basic (carbon monoxide) oxides, depending on the conditions of the reaction.

Some common laboratory acids that you may have encountered in Class VII include hydrochloric acid, sulfuric acid, and nitric acid. These acids are formed when non-metals (chlorine, sulfur, and nitrogen, respectively) react with oxygen to form oxides.

Some common laboratory bases that you may have encountered in Class VII include sodium hydroxide, potassium hydroxide, and calcium hydroxide. These bases are formed when metals (sodium, potassium, and calcium, respectively) react with oxygen to form oxides.

Reaction with Water

When sodium metal reacts with water, it produces sodium hydroxide (a base) and hydrogen gas. The reaction is highly exothermic, meaning that it releases a lot of heat. The heat of the reaction can cause the hydrogen gas to ignite, resulting in a fire or explosion. For this reason, sodium metal is typically stored in kerosene, which helps to prevent contact with water and oxygen.

Calcium metal also reacts with water, but the reaction is not as violent as the reaction of sodium metal. Calcium metal produces calcium hydroxide (a base) and hydrogen gas when it reacts with water. The reaction is still exothermic, but it is not as explosive as the reaction of sodium metal with water.

Other metals, such as iron, do not react as quickly or violently with water. Iron reacts with water slowly to produce iron oxide (rust) and hydrogen gas.

On the other hand, non-metals such as carbon, sulfur, and chlorine do not react with water under normal conditions. However, some non-metals, such as hydrogen and oxygen, can react with water to form acids. For example, when hydrogen gas reacts with water, it produces hydrochloric acid (HCl). When oxygen gas reacts with water, it produces hydrogen peroxide (H2O2).

Very reactive non-metals, such as phosphorus, can catch fire when exposed to air. To prevent the contact of phosphorus with atmospheric oxygen, it is stored in water, which helps to exclude oxygen and prevent the risk of fire.

Reactions with Acids

Metals and non-metals generally behave differently when they come into contact with acids.

Metals tend to react with acids to produce hydrogen gas and a salt. The reaction of a metal with an acid is an oxidation-reduction reaction, in which the metal is oxidized and the acid is reduced. For example, when zinc metal reacts with hydrochloric acid, it produces zinc chloride (a salt) and hydrogen gas:

Zn + 2 HCl → ZnCl2 + H2

When a burning match is brought near the mouth of a test tube containing a metal reacting with an acid, the hydrogen gas produced in the reaction can ignite, producing a "pop" sound.

Under normal conditions, non-metals do not tend to react with acids. However, some non-metals, such as oxygen and sulfur, can react with strong acids to produce hydrogen peroxide (H2O2) and sulfur dioxide (SO2), respectively.

Copper is a metal that does not react with dilute hydrochloric acid, even when heated. However, copper does react with concentrated sulfuric acid to produce copper sulfate (CuSO4) and sulfur dioxide (SO2).

Overall, the behavior of a substance when it comes into contact with an acid depends on the reactivity of the substance and the strength of the acid.

Reactions with Bases

The "pop" sound that is sometimes heard when a burning match is brought near the mouth of a test tube or other container indicates the presence of hydrogen gas. Hydrogen gas is flammable and will ignite when it comes into contact with a spark or flame.

Metals can react with sodium hydroxide, a strong base, to produce hydrogen gas. For example, sodium aluminate is obtained through the reaction of aluminum with sodium hydroxide. The reaction can be represented by the following equation:

2 Al + 2 NaOH + 2H2O -> 2 NaAlO2 + 3H2

Reactions of non-metals with bases are generally more complex than reactions of metals with bases. Non-metals may react with bases to produce a salt and water, or they may not react at all. The behavior of a non-metal when it comes into contact with a base depends on the reactivity of the non-metal and the strength of the base.

Displacement Reactions

Copper Sulphate (CuSO4) (Blue) + Zinc (Zn) → Zinc Sulphate (ZnSO4) ( Colourless) + Copper (Cu) (Red)

In this reaction, the blue color of the copper sulphate solution disappears and a powdery red mass of copper is deposited at the bottom of the beaker. This is due to the displacement of copper by zinc, as zinc is more reactive than copper and is able to displace it from the copper sulphate compound. The reaction can be represented by the equation above.

The sequence of metals (among zinc, iron and copper) from more reactive to less reactive is: zinc > iron > copper. This means that zinc is the most reactive metal, followed by iron and then copper.

This can be explained by the reactivity series, which is a list of metals arranged in order of their reactivity. The more reactive a metal is, the higher it is on the list and the more likely it is to displace less reactive metals from their compounds.

Uses of Metals and Non-metals

Metals are used in a variety of applications because they have useful physical and chemical properties. Some examples of the uses of metals include:

Making machinery, automobiles, airplanes, trains, and satellites: Metals are strong and durable, making them ideal for use in the construction of these types of products.

Industrial gadgets: Metals are resistant to corrosion and can withstand high temperatures, making them suitable for use in industrial processes.

Cooking utensils: Many cooking utensils are made of metals such as aluminum, copper, or stainless steel because they are good conductors of heat.

Water boilers: Metal water boilers are able to withstand high temperatures and pressures, making them suitable for use in the heating of water.

Some examples of the uses of non-metals include:

Oxygen (O2): Oxygen is a non-metal that is essential for life because it is inhaled during breathing.

Nitrogen (N2): Nitrogen is a non-metal that is used in fertilizers to enhance the growth of plants.

Chlorine (Cl2): Chlorine is a non-metal that is used in the water purification process.

Iodine (I2): Iodine is a non-metal that is used in a purple-colored solution applied on wounds as an antiseptic.

Sulfur (S): Sulfur is a non-metal that is used in the production of crackers.

Magnesium is an esential element for plants and is found in them in the form of magnesium ions. These ions are involved in a variety of processes in plants, including the synthesis of chlorophyll, the activation of enzymes, and the transportation of nutrients.

Iron is an essential element for the human body and is found in a number of tissues and organs. The body stores most of its iron in the bone marrow, where it is used to produce red blood cells. Iron is also found in small amounts in other tissues, such as the liver, spleen, and muscles.

Iron deficiency is a common condition that occurs when the body does not have enough iron to produce sufficient red blood cells. This can lead to symptoms such as fatigue, weakness, and difficulty concentrating. Iron deficiency can be treated by increasing the intake of iron-rich foods or by taking iron supplements.

Atoms and Elements

In a chemical reaction, new substances are formed as a result of the rearrangement of atoms. If a substance cannot be broken down further by chemical reactions, cooling, heating, or electrolysis, it is considered to be an element. An element is a pure substance that is made up of only one type of atom, and it cannot be decomposed into simpler substances by ordinary chemical means. There are around 94 naturally occurring elements, and these form the building blocks for all of the substances in the universe. Elements can be classified as metals, non-metals, or metalloids based on their properties.