Based on the chemical constitution, matter is classified into two kinds: Substances and Mixtures. Substances are further classified into elements and compounds.
Elements
What is an element?
Element is the basic constituent of all matter. An element is the simplest form of matter, which can’t be split into simpler substances by any chemical or physical method.
In terms of the atomic theory, an element is composed of atoms of the same kind. There are 118 elements known to us at present out of which 92 are naturally occurring while remaining have been prepared artificially.
These elements are widely distributed in the earth’s crust in the free as well as the combined state.
On the basis of chemical and physical properties, the elements are further classified into:
- Metals
- Non-metals
- Metalloids
Only a few elements occur in their pure form. Most elements are present in nature in the combined form, i.e., in the form of their compounds. Common elements cannot be made in a laboratory.
However, certain element can be made in very small amounts by using special techniques in laboratory.
Metals
The elements, except hydrogen, which form positively charged ions, i.e., cations, by losing electrons in all the chemical reaction are called metals. Thus, metals are electropositive elements.
Metals are malleable, ductile and conductor of heat and electricity.
What are the physical properties of metals?
All metals show similar physical properties. However, there are a few exceptions:
- Physical state: Under normal pressure, all metal except mercury are solids at room temperature. Mercury is liquid at room temperature.
- Colour: Most metals except gold and copper are silvery-grey in colour. Copper is reddish-brown and gold is golden-yellow.
- Appearance: All metals are shiny. The characteristic shine of metals is called metallic luster. Thus, all metals have metallic luster. Metals can be easily polished.
- Hardness: Most metals are hard except sodium and potassium. Sodium and potassium metals can be easily cut with a knife. Osmium is hard enough to scratch glass.
- Tensile strength: Metals, except sodium and potassium, have high tensile strength. Metals are very strong, e.g., iron can bear a lot of stress, that’s why, it is widely used in construction of buildings, bridges, railway lines, etc.
- Malleability: Metals are malleable. This means that metals can be hammered into very thin sheets. Silver can be beaten into very thin leaves. You must have seen silver varak on barfi (sweet). Aluminium foil is used in packaging of food materials.
- Ductility: Metals are ductile. This means that metals can be drawn into thin wires. Silver and gold and drawn into very thin wires.
- Conductivity: Metals are good conductor of heat and electricity. Silver is the best conductor of electricity. Copper is the also best conductor of electricity.
- Density: Metal, except sodium and potassium, have high densities. Sodium and potassium have much lower densities.
- Sound: Metals are sonorous. Metals when hit by a hammer produce ringing sound, that’s why, metals are used for making bells and wires for musical instruments.
Non-metals
The elements which form negatively charged ions, i.e., anions, by gaining electrons in all chemical reactions are called non-metals. Thus, non metals are electronegative elements. Non-metals are neither ductile nor malleable, and do not conduct electricity, except graphite. Graphite is the only non-metal which conducts electricity.
What are the physical properties of non-metals?
Some physical properties of non-metals are:
- Physical state: Non-metals may occur as solids, liquids or gases at room temperature, e.g., under normal conditions sulphur, phosphorus are solid, bromine is a liquid and hydrogen, oxygen, nitrogen are gases.
- Colour: Non-metals come in many colours, e.g., sulphur is yellow, phosphorus is white or red, chlorine is greenish-yellow, bromine is a reddish-brown and hydrogen, oxygen & nitrogen are colourless.
- Appearance: Non-metals have a dull appearance. They do not shine. However, diamond, graphite and iodine are the only non-metals which have metallic lusture.
- Malleability and ductility: Non-metal are neither malleable nor ductile. Non-metals cannot be drawn into wires and beaten into sheets. Non-metals are brittle in nature, i.e., non metal break up into pieces when press hard or hammered.
- Conductivity: Non-metals do not conduct heat and electricity. Non-metals are insulators. However, graphite is a good conductor of heat and electricity.
- Density: Non-metals usually have low density and are soft in nature. Diamond is an exception. It is the hardest natural substance known.
- Tensile strength: Non-metals have low tensile strength. They can be easily broken.
- Melting and boiling points: Non-metals, except graphite, have low melting and boiling points.
- Sound: Non-metals do not produce sound when hit with an object. Non-metals are non-sonorous.
Chemical compound
All compound are formed as a result of chemical reaction, so compounds are also called chemical compounds.
What is a chemical compound?
Two or more elements combined together chemically to form a new substance called compound. Compounds are commonly termed as chemical compounds, because these are formed due to a chemical reaction between two or more elements. Hence,
A compound is a pure substance made up of two or more elements combined chemically in a definite or constant proportion by mass.
e.g., water is a chemical compound made by hydrogen and oxygen combine in the ratio 2:1 by volume or 1:8 by mass, i.e., 2 gram of hydrogen combines with 16 gram of oxygen, pure sodium chloride contains 66% of chlorine by mass.
What are the characteristics of a chemical compound?
A chemical compound has the following characteristics:
- A chemical compound is obtained by the chemical combination of two or more elements in a definite proportion by mass.
- Compounds are homogeneous, i.e., their properties are the same throughout.
- The physical and chemical properties of a compound are entirely different from those of the constituent elements, e.g., hydrogen is a combustible gas, while oxygen is a supporter of combustion, but their compound, water is neither combustible nor a supporter of combustion.
- During the formation of a compound from its elements, a certain amount of energy in the form of heat, light or electricity is either absorbed or evolved. For example, on burning carbon ,it react with oxygen to form a gas called carbon dioxide, and heat is liberated. Carbon dioxide is a chemical compound, and its formation from the elements involve the evolution of heat.
How do mixtures differ from compounds?
Mixtures differ from compounds as follows:
| SNo. | Mixture | Chemical Compound |
| 1. | A mixture is a heterogeneous, except solutions which are homogeneous. | A chemical compound is always homogeneous. |
| 2. | The components of a mixture may be present in any proportion. | The components of a compound are present in a fixed proportion. |
| 3. | Properties of a mixture of the average properties of the components. | Properties of a compound are entirely different from those of the component elements. |
| 4. | The components of a mixture can be separated by simple physical methods. | The component of a compound cannot be separated by simple physical methods. |
| 5. | During the preparation of a mixture, no heat, light or electricity is absorbed or evolved. | Formation of a compound involves the absorption or evolution of energy, such as heat, light or electricity. |
Read More: Is Matter Around Us Pure?
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