இந்தக் கட்டுரையில், TNPSC குரூப் 1, குரூப் 2, குரூப் 2A, குரூப் 4 மாநிலப் போட்டித் தேர்வுகளான TNUSRB, TRB, TET, TNEB போன்றவற்றுக்கான  முறைகள் இலவசக் குறிப்புகளைப் பெறுவீர்கள்.தேர்வுக்கு தயாராவோர் இங்குள்ள பாடக்குறிப்புகளை படித்து பயன்பெற வாழ்த்துகிறோம்.

Elements and Compounds

Elements

• An element is a pure substance that cannot be broken down by chemical methods into simpler components.
• Elements consist of only one type of atoms. An atom is the smallest particle of an element that still has the same properties of that element.

Compounds

• A compound is a pure substance which is formed due to the chemicalcombination of two or more elements in a fixed ratio by mass.
• The properties of a compound are different from those of its constituents.

Classification of Elements

• Total elements – 118
• Natural elements – 94
• Artificial elements – 24

Based on their properties.They are classified into

• Metals
• Non – Metals
• Metalloids

Physical properties of Metals

• Metals are solid under normal conditions of temperature and pressure.
• Most metals are hard.
• All metals are shiny. The typical shine of metals is called metallic lustre.
• Metals generally have high density.
• Metals in general have high melting point and boiling point.
• Metals can be hammered into very thin sheets. This tendency of metals is called malleability. Using this property aluminum is transformed into silvery foils.
• Metals can be drawn into thin wires. This property of metals is called ductility. Example: Copper wires.
• Generally metals are good conductors of heat and electricity.
• 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.
• They are electro positive(Lose electrons)
• Metals gets oxidized with non metals

Uses of Metals

• Iron is used for making bridges, engine parts, iron-sheets and bars.
• Copper is used for making electrical wires, coins and statue.
• Silver and gold are used for making jewels, and for 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.
• Lead is used in automobile batteries, X-ray machines.

Properties of Non-metals

• Non-metals occur as solids, liquids or gases at normal temperature. For example,sulphur and phosphorus occur in solid state while bromine occurs in liquid state.
• Elements like oxygen, nitrogen etc., occur in gaseous state.
• Non-metals are generally not hard except diamond ( a form of carbon).
• Non-metals have a dull appearance.
• Non-metals are generally soft and have low densities. The exception here is diamond (a form of carbon) which is the hardest naturally occurring substance.
•  Non-metals have low melting point and boiling point.
• Non-metals are non-malleable.
• Non-metals are not ductile. Carbon fibre is highly ductile.
• Non-metals are generally bad conductors of electricity. Graphite (a form of carbon) is an exception.
• Non-metals do not produce sound (non sonorous) when hit.
• They are electro negative(Gain electrons).
• They get reduced with the metals

Uses of Non-metals

• Diamond (a form of carbon) is used for making jewels, cutting and grinding equipments. 
• Graphite is used in making pencil lead.
• Sulphur is used in the manufacturing of gun powder and vulcanization of rubber.
• Phosphorus is used to make match boxes,rat poison etc.
• 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. Hydrogen is also used as a reducing agent.

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