Materials: Metals and Non-metals PDF

# Materials: Metals and Non-metals ## Learning Outcomes - Occurrence of Metals and Non-metals - Physical Properties of Metals and Non-metals - Chemical Properties of Metals and Non-metals - Differences between Metals and Non-metals - Metallic Corrosion and Alloys - Uses of Metals and Non-metals #...

# Materials: Metals and Non-metals ## Learning Outcomes - Occurrence of Metals and Non-metals - Physical Properties of Metals and Non-metals - Chemical Properties of Metals and Non-metals - Differences between Metals and Non-metals - Metallic Corrosion and Alloys - Uses of Metals and Non-metals ## Occurrence of Metals and Nonmetals There are 118 known elements so far. About 91 of them show metallic properties. Metals and non-metals are abundantly available in nature. They are available in the free state as elements or in combined states as compounds. The earth's crust is abundant in many metals and non-metals. Non-metals such as silicon, oxygen and carbon are abundantly present in the earth's crust. Metals such as sodium, iron, copper and aluminium are present in large quantities in the earth's crust. The combined state in which metals exist in the earth's crust is called mineral. For example, iron is present mostly as oxides. Most of the rocks are minerals. However, all minerals are not rich sources of metals. The minerals from which metals are extracted profitably are called ores. For example, haematite and magnetite are important ores of iron. The table on the next page depicts some important ores and the metals that are extracted from them. Metals such as gold, silver and platinum exist in pure forms, i.e., in their native states. They are least reactive and do not combine with other elements to form compounds. Hence, they are called noble metals. Non-metals also exist in both free and combined states. You have studied in the previous class that nitrogen and oxygen are the major components of air. Hydrogen in combined form exists in water, hydrocarbons (compounds of hydrogen and carbon), petroleum products, etc. Oxygen is the most abundant non-metal in the Earth's crust. Carbon occurs in free state as graphite and diamond. In the Earth's crust, it occurs as carbonates and fossil fuels, i.e., coal and petroleum. Sulphur exists as sulphides and sulphates in the free state as well as combined state in the Earth's crust. Let us understand the properties of metals and non-metals. ### Good to Know Of the 118 elements, only 20 are non-metals. ## Physical Properties of Metals and Non-metals ### Physical properties of metals Metals have distinct physical properties, which differentiate them from non-metals. In your previous classes, you studied that appearance, strength, state of matter, density, conductivity, etc., are physical properties of materials. Let us explore more about the physical properties of metals. **Appearance:** How does silver and iron look different from carbon? Silver and iron appear to be shiny, whereas carbon appears dull and black. The shiny appearance of any material is called lustre. Metals have a shiny surface or lustre. Silver has a shiny white lustre, gold has a yellow lustre, copper has a reddish-brown lustre, aluminium has a white lustre and iron has a grey appearance. **Physical state:** Materials can exist in three states-solids, liquids and gases. All metals exist in solid state at room temperature. Mercury is the only metal that occurs as a liquid at room temperature. **Density:** Density refers to how close the atoms are packed in the substance. Metals have a high density. Most metals do not float on water, as the density of metals is more than that of water. **Melting and boiling point:** Most metals have high melting and boiling points. Sodium, mercury and potassium are some metals, which have comparatively lower melting and boiling points. **Hardness:** Almost all metals are hard and have high tensile strength. However, sodium and potassium are two metals that are soft and can be cut with a knife. **Sonorousness:** You might have heard a ringing sound from a metal bell when struck with a hammer. Some materials produce sound when they are struck with another object. These materials are called sonorous materials. Metals are sonorous as they produce ringing sound when struck. Due to this property of metals, they are used to make bells, wind chimes and many other musical instruments. **Lustre:** Most metals possess a shine. Metals such as gold, silver, aluminium, mercury and copper are lustrous. ### Malleability You might have seen a blacksmith beating iron or aluminium to make sheets. This property by which metals can be beaten into sheets is called malleability. Iron, silver, aluminium, tin, copper, etc., are commonly used metals, which are made into sheets. As metals are malleable, they are used to make foils, sheets and utensils. ### Ductility The property by virtue of which metals can be drawn into wires and various other shapes is called ductility. Metals such as gold and silver are used to make ornaments. Copper is used to make wires. ### Electrical conductivity Metals are good conductors of electricity. They allow electricity to pass through them. This is why electrical wires are made of copper. ### Thermal conductivity Metals are good conductors of heat. They allow heat to pass through them. For this reason, metals are very hot to touch if heated and cold to touch if cooled. Metals are preferred to make cooking utensils, as they are excellent conductors of heat. Silver is the best conductor of heat. ### Physical properties of non-metals * Some non-metals are solids at room temperature such as carbon, sulphur and phosphorus. Some non-metals exist as gases such as oxygen, nitrogen and carbon dioxide, Bromine is the only non-metal that exists as liquid at room temperature. * Non-metals are dull and do not have lustre, except iodine. * Non-metals are not malleable. When beaten, they break into small pieces. Hence, they are brittle. * Non-metals are poor conductors of electricity except graphite (a form of carbon found in pencil leads). * Non-metals are poor conductors of heat. * They are not ductile. Hence, they cannot be drawn into wires. * They are not sonorous. * They have low density as compared to metals. * They have low melting and boiling points. * Non-metals are not as hard as metals except diamond (a form of carbon). In fact, diamond is the hardest material known. ### Good to Know The chemical formula of rust is Fe₂O₃·nH₂O. ## Chemical Properties of Metals and Non-metals ### Chemical properties of metals Metals have distinct chemical properties. Chemical properties are the properties shown by a metal when it undergoes a chemical reaction. Different metals show different reactions with some common chemicals and form different products. **Reaction with oxygen:** Metals react with oxygen to form a substance called metal oxide. Sodium and potassium react vigorously in the presence of oxygen. Magnesium reacts with oxygen and forms magnesium oxide. Metal oxides are basic oxides. It means that these oxides turn red litmus, blue. **Reaction with water:** Different metals show different reactivity with water. Sodium and potassium react vigorously with water and form sodium hydroxide and potassium hydroxide respectively. Iron reacts very slowly, and copper reacts with hot water or steam. **Reaction with acids:** In the previous class, you have studied briefly about acids. Hydrochloric acid (HCl) and sulphuric acid (H₂SO₄) are the two most commonly used acids. When a metal reacts with an acid, it forms a substance called metal salt and hydrogen gas is evolved with lot of heat. Noble metals such as silver and gold do not react with acids. **Reaction with bases:** Metals react with strong bases such as sodium hydroxide (NaOH) and potassium hydroxide (KOH) with evolution of hydrogen gas. **Displacement reactions:** Metals react with salt solutions of other metals. In this type of reactions, a more reactive metal displaces a less reactive metal. These reactions are called displacement reactions. How do we know which metal is more reactive? This can be found out by displacement reactions given in the activity in Let's Try This on next page. ### Chemical Properties of Non-metals **Reaction with oxygen:** Most of the non-metals do not react with oxygen at room temperature except white phosphorus. White phosphorus readily catches fire at room temperature. Hence, it is stored in water. Non-metals such as carbon and sulphur on heating or being ignited react with oxygen to form oxides. **Reaction with water:** Mostly non-metals do not react with water. However, gases such as oxygen and chlorine can dissolve in water. **Reaction with acids and bases:** Non-metals generally do not react with acids and bases. However, some non-metals react under extreme conditions. These will be discussed in higher classes. ## Differences between Metals and Non-metals | Characteristic | Metals | Non-metals | |---|---|---| | Physical state | Exist as solids except mercury (liquid) | Exist mostly as solids and gases except bromine (liquid) | | Hardness | Mostly hard and strong except mercury | Solids usually soft except diamond | | Density | Have high density | Have low density | | Melting point | Have high melting point | Have low melting point | | Conductivity | Good conductors of heat and electricity | Mostly poor conductors of heat and electricity except graphite | | Sonorousness | Sonorous | Non-sonorous | | Malleability | Malleable | Brittle | | Ductility | Ductile | Non-ductile | | Lustre | Shiny lustre | No shiny lustre except iodine, graphite and diamond | | Oxides | Basic oxides | Acidic oxides | | Hydroxides | Basic hydroxides | Acidic hydroxides | | Salt | Metal salt | - | | Displacement | More reactive metals displace less reactive metals from their solutions. | - | Reactivity series | An arrangement of metals in the order of decreasing reactivity is called reactivity series. | - | ## Metallic Corrosion and Alloys ### Corrosion of metals The gradual deterioration or waning of metals when exposed to air and moisture is called corrosion. In the previous class, you have studied about rusting of iron. When iron is exposed to air and moisture, an orange-brown layer of rust is formed. Similarly, a greenish layer is formed on copper articles on exposure to carbon dioxide and water. Another example of corrosion is blackening of silver articles. This happens when silver is exposed to polluted air containing sulphur. Aluminium does not appear to be corroded. This is because it is very active and reacts with oxygen to form a layer of aluminium oxide. This layer forms a protective layer and prevents further action of oxygen, thereby preventing corrosion of aluminium. Due to corrosion, metals lose their shine and lustre. Rusting of iron leads to wasting of the iron metal. Rusting or corrosion of iron can be prevented by the following methods: * painting * alloying * oiling/greasing * galvanising (coating with a layer of zinc) * electroplating Metals such as gold and platinum do not react with air and water. They never lose their lustre. ### Alloys An alloy is a uniform/homogenous mixture of two or more metals, or metals and non-metals. Brass is an alloy of copper and zinc. Alloys have more advantages than metals as their properties are altered to suit the purpose. Some advantages of alloys are discussed below. * Alloys are harder than metals. Alloys of copper are harder than elemental copper. * Alloys are corrosion resistant. Many alloys are made from the metals so that they are not corroded. For example, stainless steel, an alloy of iron does not rust at all. * Sometimes alloys are more malleable and ductile so that they can be used to make jewellery and decorative articles. Brass and bronze, which are alloys of copper, are more malleable and ductile. Hence, they are used to make decorative articles. * The melting points of alloys are lower than melting points of metals. Solder, which is an alloy of lead and tin, has lower melting point. Hence, it is used for joining wires and devices in electric circuits. * ## Uses of metals and non-metals ### Uses of metals Most metals are precious and they form the backbone of economy for a country. They are used in various fields. * Metals such as iron, aluminium, titanium, etc., are used in making parts of machinery. * Metals such as iron and aluminium are used in making the bodies of vehicles such as aircraft, buses, cars, trucks, trains, etc. * Metals such as copper and aluminium are used to make electrical wires. * Copper, aluminium, iron, etc., are used to make household articles and utensils. * Iron, tin and aluminium, etc., are used in construction of buildings and bridges. * Some noble metals such as gold and silver are used in the preparation of medicines. * Metals and their alloys such as brass, bronze, etc., are used to make coins, statues and decorative articles. * Precious metals such as gold, silver, platinum, etc., are used in making jewellery. * Steel (iron, carbon) is used in construction, vehicles, railways. * Stainless steel (iron, chromium, nickel) is used in utensils, instruments. * Solder (lead, tin) is used in joining wires and devices in circuits. * Duralium (aluminium, copper) is used in aircraft, ships, instruments. * German silver (copper, zinc, nickel) is used in utensils, jewellery, resistors (electrical devices). ### Uses of non-metals Non-metals such as oxygen, nitrogen and carbon are present in all living organisms and play very important roles in our environment. * Oxygen is used in respiration and combustion. * Sulphur is widely used in medicines and ointments. Sulphur is also used in preparation of tyres, dyes, fertilisers, explosives and many types of plastics. * Phosphorus is used in matchsticks and firecrackers. * Nitrogen, phosphorus and sulphur are extensively used in fertilisers. * Liquid nitrogen is used to preserve blood. Nitrogen gas is used in food packaging.. * Carbon in the form of graphite is used as electrodes in cells and batteries. It is also used as a lubricant. * Chlorine is used as disinfectant and for bleaching. ## Let's Revise * Elements are classified as metals and non-metals. * Most metals are solid at room temperature and have lustre, high melting and boiling points, and high density. * Metals can be drawn into thin wires due to the property of ductility. * Metals can be beaten into sheets due to malleability. * Metals are good conductors of heat and electricity, whereas non-metals are poor conductors. * Non-metals can be solids, liquids or gases, and are soft. * Non-metals are brittle. They do not exhibit malleability or ductility. * Metals react with oxygen to give basic oxides and react with water to form basic hydroxides. * Non-metals react with oxygen to give acidic oxides. * More reactive metals displace less reactive metals from their solutions. * An arrangement of metals in the order of decreasing reactivity is called reactivity series. * An alloy is a homogenous/uniform mixture of one or more metals and/or non-metals. * Alloys are harder and more corrosion-resistant than metals. * The waning of a metal due to the action of air and moisture is corrosion. ## Key Terms * **Metals** * **Non-metals** * **Minerals** * **Ores** * **Noble Metals** * **Malleability** * **Ductility** * **Sonorousness** * **Hydroxide** * **Oxide** * **Metal Salt** * **Displacement ** * **Reactivity series** * **Alloys** * **Corrosion** * **Density** * **Conductors** * **Lustre**