A pure substance is one which is made up of only one kind of particles. These particles may be atoms or molecules. So, we can also say that a pure substance is one which is made up of only one kind of atoms or molecules. So, what are the types of pure substances?
All the elements and compounds are pure substances because they contain only one kind of particles. Thus, all the elements like hydrogen, oxygen, nitrogen, chlorine, bromine, iodine, carbon etc. are pure substances. Similarly, all the compounds such as water, carbon dioxide, sodium chloride, sugar, copper sulphate, ammonium nitrate, potassium permanganate etc. are all pure substances. A pure substance is homogenous throughout its mass. A pure substance cannot be separated into other kinds of matter by any physical process. A pure substance has fixed melting point and boiling point.
An element is a substance which cannot be split up into two or more simpler substances by the usual chemical methods of applying heat, light or electric energy. For example, hydrogen is an element because it cannot be split up into two or more simpler substances by the usual methods of carrying out chemical reactions by applying heat, light or electricity.
An element cannot be split up into two or more simpler substances because it is made of only one kind of atoms. Another definition of element can be stated as: an element is a substance which is made of only one kind of atoms. For example, copper metal is made of only one kind of atoms, so copper metal is an element.
There are 115 elements known at present, out of which 92 elements occur in nature, while the remaining 23 elements have been prepared artificially. Every substance in this world is made up of one or more of these elements.
Elements can be solid, liquid or gases. Out of all the elements known to us, eleven elements are gases and 2 (bromine and mercury) are liquids at room temperature.
On the basis of their properties, all the elements can be divided into three groups:
A metal is an element that is malleable, ductile and conducts electricity. Some of the examples of metals are: iron, copper, aluminium, zinc, gold etc. all metals except mercury are solid at room temperature. Mercury is liquid at room temperature.
Properties of metals –
The important physical properties of metals are:
- Metals are malleable: This means that metals can be beaten into thin sheets with a hammer. Gold and silver are some of the best malleable materials. Aluminium foils are used for packing food items like biscuits, chocolates, medicines, cigarettes, etc.
- Metals are ductile: This means that metals can be drawn into thin wires. Gold and silver are some of the best ductile metals.
- Metals are good conductors of heat and electricity: this means that metals allow heat and electricity to pass through them. Silver metal is the best conductor of electricity and heat. Electric wires are made up of copper and aluminium metals because they are very good conductors of electricity.
- Metals are lustrous (or shiny), and can be polished: for example, gold, silver and copper are shiny metals and they can be polished. The property of a metal of having a shining surface is called metallic lustre.
- Metals are generally hard: most of the metals are hard except sodium and potassium which are soft.
- Metals are usually strong. They have high tensile strength: this means that metals can hold large weights without breaking. For example, iron metal is very strong having a high tensile strength.
- Metals are solids at room temperature: all metals like iron, copper etc. are all solids at the room temperature except mercury.
- Metals have high melting points and boiling points: this means that most of the metals vaporise at high temperatures. Sodium and potassium have low melting and boiling points.
- Metals have high densities: this means that metals are heavy substances. For example, density of iron metal is 7.8 g/cm3 which is quite high.
- Metals are sonorous: this means that metals make a ringing sound when we strike them.
A non-metal is an element that is neither malleable nor ductile, and does notconduct electricity. For example – carbon, sulphur, iodine etc. All the non-metals are solids or gases at room temperature but bromine is a liquid at room temperature.
Properties of non-metals –
- Non-metals are not malleable: This means that non-metals cannot be beaten into thin sheets with a hammer. Non-metals break into small pieces when hammered. Brittleness is a characteristic property of non-metals.
- Non-metals are not ductile: this means that non-metals cannot be drawn into wires. They are easily snapped on stretching. Non-metals are neither malleable nor ductile. Non-metals are brittle.
- Non-metals are bad conductors of heat and electricity: this means that non-metals do not allow heat and electricity to pass through them. Diamond is a non-metal which is a good conductor of heat and graphite is a good conductor of electricity.
- Non-metals are not lustrous: non-metals do not have lustre which means that non-metals do not have a shining surface.
- Non-metals are generally soft: most of the non-metals are generally soft but diamond is extremely hard.
- Non-metals are not strong: they have low tensile strength; they cannot hold large weights.
- Non-metals may be solid, liquids or gases:non-metals exist in all three physical states.
- Non-metals have comparatively low melting point and boiling point: this means that non-metals melt and vaporise at low temperatures except graphite.
- Non-metals have low densities: this means that non-metals are light substances.
- Non-metals are not sonorous: this means that solid non-metals do not make a ringing noise when we strike them.
The elements which show some properties of metals and some other properties of non-metalsare called metalloids.
A compound is a substance made up of two or more elements chemically combined in a fixed proportion by mass. For example, water is a compound made up of two elements, hydrogen and oxygen, chemically combined in a fixed proportion of 1:8 by mass. Compounds can be further divided into acids, bases and salts on the basis of their properties.
Questions related to the topic What are the Types of Pure Substances – From NCERT textbook –
What is meant by pure substance ?
A pure substance is one which is made up of only one kind of particles. These particles may be atoms or molecules. For example – sulphur is made up of only one kind of particles (called sulphur atoms), therefore, sulphur is a pure substance. Similarly, water is made up of only one kind of particles (called water molecules), therefore, water is also a pure substance. In fact, all the elements and compounds are pure substances because they contain only one kind of particles. A pure substance is homogenous throughout its mass. A pure substance cannot be separated into other kinds of matter by any physical process.
Try segregating the things around you as pure substances or mixtures.
Pure substances – naphthalene balls, sodium chloride, distilled water, alum, graphite, baking soda
Mixtures – tap water, milk, air, gold ornaments, ice-cream, brass, salt solution, steel, wood
Page 28, 29 and 30
Which of the following materials fall in the category of a “pure substance” ?
(d) hydrochloric acid
(e) calcium oxide
Pure substances are: Ice, Iron, Calcium oxide and Mercury.
Classify the following into elements, compounds and mixtures:
(c) sugar solution
(e) calcium carbonate
(l) carbon dioxide
Elements – sodium, silver, tin, silicon
Compounds – calcium carbonate, soap, methane, carbon dioxide
Mixtures – soil, sugar solution, coal, air, blood
Pure substances are those that are made up of only one kind of atoms and cannot be separated into more constituents. What are the types of pure substances? Elements and compounds are pure substances. Elements are substances which are made up of only one kind of atoms. Compounds are substances which are made up of two or more kinds of elements in a fixed proportion.