Question 2 How many elements are known till today?
Question 3 Name 2 elements which are liquid at room temperature?
Question 4 What are the three groups into which elements can be classified?
Question 5 Define the term malleable?
Question 6 Define the term ductile?
Question 7 Why Aluminium metal is used in foils?
Question 8 Why copper and aluminium metals are used in thin wires?
Question 9 Why cooking utensils are made up of copper and aluminium metal?
Question 10 Give 2 examples of lustrous metals?
Question 11 Name 2 soft metals?
Question 12 Why iron is used in the construction of building,bridges etc?
Question 13 Why metals have high melting and boiling point?
Question 14 What are non-metals?
Question 15 How will you differentiate between metals and non-metals?
Question 16 What are metalloids.Give example?
Question 17 Name one non-metal which is hard?
Question 18 Name a non-metal which is a good conductor of electricity?
Question 19 Why graphite is used for making electrode in a dry cell?
Question 20 What is meant by saying that metals are sonorous?
An element is a substance which cannot be split up into two or more simpler substance by the usual chemical methods of applying heat, light or electric energy.They are made up of only one kind of atom.
For Ex:Hydrogen, Oxygen, Copper, iron, sodium, Gold, Silver etc.At present there are 118 elements known.
Elements can be classified into 1)Metals 2)Non-Metals 3)Metalloids
METALS The important physical properties of metals are:
1)Metals are malleable:This means that metals can be beaten into thin sheets with a hammer.
For Ex:Gold,Silver,Copper,Aluminium etc.
Silver foils are used for decorating sweets. Aluminium Foils are used for packing food items.Aluminium sheets are used for making utensils. Copper is used in making utensils.
2)Metals are ductile:This means that they can be drawn into thin wires.
For Ex:Copper,Aluminium,Gold,Silver etc.
Copper and Aluminium wires are used in electrical wiring.
3)Metals are good conductor of heat and electricity:This means that metals allow heat and electricity to pass through them easily.
For Ex:Silver is the best conductor of heat and electricity.
Copper and Aluminium metals are also very good conductors and are used in cooking utensils,water boilers,electric wires. Lead and mercury are poor conductor of heat and electricity.
4) Metals are lustrous(shiny)and can be polished
For Ex:Gold,Silver,Copper etc
Due to their shiny appearance they are useful in making jewellery and decorative. The shiny surface of metals makes them good reflectors of light.
5)Metals are generally hard
For Ex:Iron,Copper,Aluminium etc are hard.They can not be cut with knife.Sodium And potassium are exception.They are soft metals and can be cut with knife easily.
6)Metals have high tensile strength(strong)
For Ex:Iron metal is very strong and has very high tensile strength.Due to which it is used in the construction of bridges,building,railways,machines,vehicles etc.
Sodium and Potassium are not strong metals.
7)Metals are solids are room temperature All metals like copper,aluminium,silver,gold etc are solid at room temperature.
Mercury is the only metal which is liquid at room temperature.
8)Metals have high melting and boiling point Iron has highest melting point of 1535°C
Copper has melting point of 1083°C
Sodium and Potassium have low melting point.
9)Metals have high densities
Density of iron is 7.8 g/cm3 which is quite high.
Sodium and Potassium metal have low density.
10)Metals are sonorous:This means that metals make a ringing sound when we strike them.
11)Metals usually have a silver or grey colour
Except copper and gold
The important physical properties of non-metals are:
1)Non-Metals are not malleable:This means that non metals can not be beaten into thin sheets with a hammer.They break into small pieces when hammered.They are brittle in nature.
For Ex: Sulphur ,Phosphorus
2)Non-Metals are not ductile:This means that they can not be drawn into thin wires.
For Ex: Sulphur,Phosphorus.When stretched, Sulphur and Phosphorus break into pieces and do not form wires.
3)Non-Metals are bad conductor of heat and electricity:This means that they do not metal allow heat and electricity to pass through them easily.
For Ex: Sulphur ,Phosphorus
Diamond is a non-metal which is a good conductor of heat. Graphite is a non-metal which is a good conductor of electricity.Therefore it is used for making electrodes.
4) Non-Metals are not lustrous.
They have dull appearance.
For Ex: Sulphur ,Phosphorus.Iodine is a non-metal having lustrous appearance.
5) Non-Metals are generally Soft
They can be easily cut with knife.
For Ex: Sulphur ,Phosphorus.
Diamond(allotrope of carbon) is very hard.
6)Non-Metals have low tensile strength(not strong)
7)Non-Metals are solids,liquid or gases at room temperature.
For Ex:Carbon,sulphur,phosphorus are solids.
Bromine is a liquid. Hydrogen,oxygen,nitrogen etc are gases.
8)Non-Metals have low melting and boiling point
Only graphite has high melting point.
Most of the non-metals has very low boiling point due to which they exist as gases at room temperature.
9)Non-Metals have low densities
Iodine is the only non-metal having high density.
10)Non-Metals are not sonorous
11) Non-metals have many different colours.
For Ex: Sulphur is yellow Phosphorus is red or white Chlorine is yellowish-green Bromine is red-brown.
METALLOIDS The elements which show some properties of metals and some other properties of non-metals are called metalloids.