Matter Online Test 8th Science Lesson 4 Questions in English

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In the universe all manifestations, phenomena and evolution of life are caused by matter and energy. The various objects which exist around us are made of some kind of matter.

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We perceive some of these objects through our senses like sight, touch, hearing, taste and smelling. A glass tumbler can be seen, agarbatti burning can be recognized by its smell whereas wind blowing can be felt.

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All kinds of matter possess mass and occupy space, of course some are heavy and others are light. Thus, matter can be defined as anything, which occupies space or volume and mass and can be perceived by our senses.

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As we know already matter exists in:

 Solids: Substances like wood, stone, sand, iron etc.

 Liquids: Substances like water, milk, fruit juice, etc

 Gases: Substances like oxygen, nitrogen, carbon dioxide, steam, etc.,

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Matter in any physical state is composed of smaller particles such as atom, molecules or ions. Molecules are also made up of atoms of same or different kinds. Hence, atoms are the building blocks of matter.

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An atom is the smallest particle of an element, which exhibits all the properties of that element. It may or may not exist independently but takes part in every chemical reaction.

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Atoms of the same element or different elements combine to form a molecule. A molecule is the smallest particle of a pure substance (element or compound), which can exist independently and retain the physical and chemical properties of the substance.

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The symbols in form of the geometrical shapes were those used by the ancient Greeks to represent the four basic elements around us such as earth, air, fire and water.

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In the days of alchemists, the different materials that they used were represented by the above- mentioned symbols while they try to change less valuable metal into gold. The process was called alchemy and the men who did this work were known as alchemists.

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In 1808, John Dalton, English scientist tried to name the various elements based on these pictorial symbols. These symbols are difficult to draw and hence they are not used. It is only of historical importance.

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In 1813, Jon Jakob Berzelius devised a system using letters of alphabet rather than signs.,. The modified version of Berzelius system follows under the heading ‘System for Determining Symbols of the Elements’.

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Symbol of an element signifies:

 Name of the element

 One atom of the element

 For example, the symbol O stands for the element of Oxygen, One atom of oxygen

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The progress of man towards civilization is linked with the discovery of several metals and non- metals. Even today, the index of prosperity of a country depends upon the amount of metal and non-metals it produces and uses.

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The wealth of a country is measured by the amount of gold in its reserve. These days, metals and non-metals are used for making tools, machines, cars, utensils, etc. Some of the common metals used are iron, copper, silver, gold, lead, zinc, aluminium, magnesium, nickel, chromium and mercury etc. Similarly, the common non-metals used are nitrogen, oxygen, hydrogen, carbon, sulphur, phosphorus and chlorine etc.

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An element can be identified as metal or non-metal by comparing its properties with the general properties of metals and non- metals. In doing so, we find that some elements neither fit with the metals or with non-metals. Such elements are called semi-metals or metalloids. Elements are classified into metals, non-metals, and metalloids based on their properties.

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Metals are solid under normal conditions of temperature and pressure. Mercury is liquid at room temperature. Elements Caesium (Cs), rubidium (Rb), Francium (Fr) and Gallium (Ga) become liquid at or just above room temperature

Most metals are hard. The exception here is sodium and potassium, which is soft enough to be cut by a knife. Osmium is so hard that it can scratch glass.

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All metals are shiny. Th e typical shine of metals is called metallic lustre. All metals have a typical metallic lustre. An exception is calcium.

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Metals generally have high density. Sodium and potassium have exceptionally low density. All metals have a typical metallic lustre.

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Melting point and boiling point: Metals in general have high melting point and boiling point. Sodium, potassium, mercury and gallium are exceptions.

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Metals have the capacity to withstand strain without breaking. This property is called tensile strength. It is the property that owes the use of iron for the construction of railway tracks. Zinc, arsenic and antimony are exceptions

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Metals can be hammered into very thin sheets. Th is tendency of metals is called malleability. Aluminium makes use of this property to transform into silvery foils.

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Ductility: Metals can be drawn into thin wires. This property of metals is called ductility. Example: copper wires.

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Metals are good conductors of heat and electricity. Silver and copper are very good conductors of electricity. However, bismuth and tungsten are poor conductors.

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On being hit, metals produce a typical sound. Hence, they are said to be sonorous. This property is being made used in making temple bells.

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Elements that generally do not shine, neither too hard nor too soft, are non-metals. All gases are non-metals. Some non-metals are Sulphur, Carbon, Oxygen etc.

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Non-metals occur as solids, liquids or gases at normal temperature, for example sulphur, phosphorus occurs in solid state while bromine occurs in liquid state. Gases like oxygen, nitrogen, etc., occur in the gaseous state.

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Non-metals are generally not hard except diamond (a form of carbon). Non-metals have a dull- appearance; Graphite and iodine are exceptions as they are shiny.

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Nonmetals have low melting point and boiling point. However, carbon, silicon and boron are exceptions. Non-metals do not have tensile strength. However, carbon fibre (a form of carbon) is as tensile as steel.

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Uses of Metals:

 Iron is used for making bridges, engine parts, iron-sheet and bars.

 Copper is used for making electrical wires, coins and statue.

 Silver and gold are used for making jewels, in decorative purposes and photography

 Mercury is used in thermometers and barometers because of its high density and uniform expansion at different temperature.

 Aluminium is used in electrical wires, cables and in aerospace industries.

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Diamond (a form of carbon) is used for making jewels, cutting and grinding equipment. Graphite is used in making pencil lead.

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Sulphur is used in the manufacturing of gun powder and vulcanization of rubber. Phosphorus is used in matches, rat poison etc.

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Nitrogen is used for manufacturing ammonia. Chlorine is used as a bleaching agent and in sterilizing water. Hydrogen is used as a rocket fuel and hydrogen flame is used for cutting and welding purposes, as well as a reducing agent.

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The elements which exhibit the properties of metals as well as non-metals are called metalloids. Examples: boron, silicon, arsenic, germanium, antimony, tellurium and polonium.

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Physical properties of metalloids:

Metalloids are all solid at room temperature

 They can form alloys with other metals

 Some metalloids, such as silicon and germanium, can act as electrical conductors under the specific conditions, thus they are called semiconductors.

 Silicon for example appears lustrous, but is not malleable nor ductile (it is brittle – a characteristic of some non-metals). It is a much poorer conductor of heat and electricity than the metals

 The physical properties of metalloids tend to be metallic, but their chemical properties tend to be non-metallic

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Water, carbon di oxide, sodium chloride etc. are few examples of compounds. A molecule of water is composed of an oxygen atom and two hydrogen atoms in the ratio 1:2 by volume or 8:1 by mass.

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