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Thursday, 23 February 2017

Some Basic Concepts of Chemistry IV


Elements
An element is the simplest form of matter that cannot be split into simpler substances or built from simpler substances by any ordinary chemical or physical method. 
There are 114 elements known to us, out of which 92 are naturally occurring while the rest have been prepared artificially.

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


Compounds

A compound is a pure substance made up of two or more elements combined in a definite proportion by mass, which could be split by suitable chemical methods.

Characteristics of compound

  1. Compounds always contain a definite proportion of the same elements by mass. The properties of compounds are totally different from the elements from which they are formed.
  2. Compounds are homogeneous
  3. Compounds are broadly classified into inorganic and organic compounds
  4. Inorganic compounds are those, which are obtained from non-living sources such as minerals. For example, common salt, marble and limestone
  5. Organic compounds are those, which occur in living sources such as plants and animals. They all contain carbon. Common organic compounds are oils, wax, fats etc.
Mixtures
  1. A mixture is a combination of two or more elements or compounds in any proportion so that the components do not lose their identity. Air is an example of a mixture Mixtures are of two types, homogeneous and heterogeneous
  2. Homogeneous mixtures have the same composition throughout the sample. The components of such mixtures cannot be seen under a powerful microscope. They are also called solutions. Examples of homogeneous mixtures are air, seawater, gasoline, brass etc
  3. Heterogeneous mixtures consist of two or more parts (phases), which have different compositions. These mixtures have visible boundaries of separation between the different constituents and can be seen with the naked eye e.g., sand and salt, chalk powder in water etc.
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