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Types of Substances

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Types of Substances - Lesson Summary

Types of substances:  Substances are classified into two types. They are,

Pure Substance:  A substance which is made of one kind of particle.
Examples - iron, aluminium, silver and gold.

Mixtures:  A substance which contains two or more different particles is known as mixtures.
Example: Salt solution is made up of two components, salt and water. Therefore,salt solution is a mixture.



Pure Substances: Types
On the basis of their chemical composition, pure substances are classified as elements and compounds.

Element:  A pure substance which is made up of only one kind of atom and cannot be broken into two or more simpler substances by physical or chemical means is referred to as an element.

Characteristics of elements are:
  • An element is homogeneous in nature; it is a pure substance, made up of only one kind of atoms. For example, iron and silver are made of only iron and silver atoms.
  • An element cannot be broken down into simpler substances by any physical or chemical methods such as heat, light electricity, or chemical reactions with other substances. For example, if you were to smash a piece of iron into smaller pieces or heat it, the piece still remains as the element iron.
  • An atom is the smallest unit that shows all the properties of an element. For example, an atom of iron shows all the properties of that metal.
  • Elements have sharp melting and boiling points. 

Elements are classified as metals, non-metals and metalloids.

Metals:  Metals are the elements that readily loose an electron to form a positive ion or cation. 

Example: Gold, silver, copper, iron, potassium etc.

Properties of Metals:

  • Metals have lustre. When freshly cut, they show metallic lustre. Example: Gold.
  • Metals are good conductors of heat and electricity. As metals have free electrons in them, they are able to conduct heat and electricity. Example:  Copper
  • Metals are malleable, meaning they can be hammered into thin sheets. Example: Aluminum
  • Metals are ductile, which means they can be drawn into wires.
  • Metals are sonorous. They give a ringing sound when they are hit by a hard iron rod. Example: copper.
  • Almost all metals are solids at room temperature.


Exceptions:

  • Sodium and potassium are soft metals.
  • Mercury is liquid at room temperature.
  • Zinc is brittle in nature, it is non-ductile and non-malleable.
  • Tungsten is a poor conductor of electricity


Non - metals:  Non - metals are those elements that readily gain an electron(s) to form a negative ion or anion.
Example: Hydrogen, Oxygen, Iodine etc.

Properties of Non-metals:

  • Non-metals exist as solids, liquids and gases.
  • Example: Silicon and carbon are solids; bromine is a liquid; chlorine, fluorine and oxygen are gases.
  • Non-metals are non-lustrous, that is, they have a dull appearance. 
  • Example: The surfaces of sulphur and phosphorus do not shine.
  • Most non-metals have very low density.    
  • Example: Oxygen and nitrogen are lighter than air.
  • The exception is diamond, a form of carbon. Diamond is one of the strongest known substances.
  • Non-metals are not malleable.  
  • Example: Sulphur and iodine cannot be hammered into sheets.
  • Non-metals, except for carbon fibres, are not ductile.                                                      
  • Example: Phosphorous and Bromine cannot be drawn into wires.
  • Non-metals are bad conductors of heat and electricity. 
  • Example: Nitrogen and Oxygen cannot conduct electricity.
  • The exception is graphite, a form of carbon which is a good conductor of electricity.
  • Non-metals have low melting and boiling points.
  • Example: Sulphur and Phosphorus have


Metalloids:  The elements which have intermediate properties between those of metals and non-metals are called metalloids.

  • They are amphoteric in nature.
  • Metalloids react both with acids and bases.
  • For example, boron, silicon and germanium.


Compound:  A pure substance composed of two or more elements that are chemically combined in a fixed proportion is called a compound.
Example: Water

Properties of a compound:

  • A compound is homogeneous in nature, made up of the same type of molecules.
  • For example, water contains only molecules of water.
  • The components of a compound cannot be separated by physical methods but they can be separated by chemical and electrochemical methods                                                        
  • For example, water can be broken into constituent elements hydrogen and oxygen by the process of electrolysis.
  • A compound has a fixed composition.                                                                          
  • For example, a water molecule is always composed of two hydrogen atoms and one oxygen atom.
  • A compound has a distinct set of properties which is not similar with the properties of its constituent elements.                                                                                                  
  • For example, sodium chloride table salt is a harmless substance which is a white crystalline solid. On the other hand, its constituents sodium is a greyish white solid and chlorine isare a greenish yellow gas that is potentially dangerous.
  • A compound has a sharp melting and boiling point.                                                       
  • For example,  water has a boiling point of 1000C, and a melting point of 0 0C


Mixtures:  Matter that consists of two or more substances which may be elements, compounds or both mixed together physically in any proportion, but not chemically combined.

Properties of mixture:

  • There is no definite proportion in which the constituents of a mixture combine.
  • For example, the mixture of salt and sand can be in any ratio.
  • The parts of a mixture can be separated by physical means.
  • For example, a mixture of iron filings and sulphur can be separated by using a magnet.
  • When a mixture is created, no new substance is formed; each part of a mixture retains its own properties
  • For example, we could mix various proportions of hydrogen and oxygen gas, as long as you do not ignite the mixture, the combination will form a mixture that can be separated.
  • Energy is neither given out nor absorbed in the preparation of a mixture
  • For example, no heat or light energy is liberated or absorbed when iron filings and sulphur are mixed together.
  • A mixture does not have a sharp melting or boiling point.
  • For example, sugar solution does not boil at a fixed temperature.


Mixture: Classification:  Mixtures are classified into homogeneous and heterogeneous types.

Homogeneous mixture:  A mixture in which various constituents are mixed uniformly is called homogeneous mixture.
 Example: Air, Alloy, Solution of salt in water.

Heterogeneous mixture:  A mixture that is not uniform throughout is called a heterogeneous mixture.
Example: A mixture of sugar and salt is a heterogeneous mixture.

Differences between a mixture and a compound:

                           Mixture                            Compound It consists of two or more substances which may be elements, compounds or both mixed together physically in any proportion, but not chemically combined. It consists of two or more elements that are chemically combined in a fixed proportion. It may be homogeneous or heterogeneous It is always homogeneous The parts of a mixture can be separated by physical means. The components of a compound cannot be separated by physical methods but they can be separated by chemical and electrochemical methods Each component of a mixture retains its individual properties. A compound has a distinct set of properties which is not similar to the properties of its constituent elements.    Energy is neither given out nor absorbed in the preparation of a mixture. Heat is taken in or given out in the preparation of a compound. A mixture does not have a sharp melting or boiling point. A compound has a sharp melting and boiling point.  

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