Formula of Binary Compounds


 
 
Concept Explanation
 

Formula of Binary Compounds

Writing chemical formulae: The shortest way to represent a compound with the help of symbols and valency of elements is known as chemical formula. Chemical formula of a compound shows its constituent elements and the number of atoms of each combining element. In ionic compounds, the charge on each ion is used to determine the chemical formula of a compound. There are some rules for writing the chemical formula:

  • The valencies or charges on the ion must be balanced.
  • When a compound consists of a metal and a non-metal, the symbol of the metal is written first and on the left whereas of non-metal on its right. E.g. calcium oxide (CaO), sodium chloride (NaCl), iron sulphide (FeS), copper oxide (CuO) etc., where oxygen, chlorine, sulphur are non-metals and are written on the right, whereas calcium, sodium, iron and copper are metals and are written on left.
  • When compound is formed with polyatomic ions, the ion is enclosed in a bracket before writing the number to indicate the ratio. e.g. large bg_white Ca(OH)_2
  • In case if the number of polyatomic ion is one, the bracket is not required. e.g. NaOH.

    Formulae of Simple Compounds: To write the chemical formula for simple compounds:

  • Write the symbols of constituent elements and their valencies.
  • Write the symbol of cation first followed by the symbol of anion.
  • Then criss-cross their charges or valencies to get the formula.
  • The positive and negative charges must balance each other and the overall structure must be neutral.
  • Sample Questions
    (More Questions for each concept available in Login)
    Question : 1

    Arrange the statements in a systematic way of writing the chemical formula for simple compounds:

    (a) Write the symbol of cation first followed by the symbol of anion.

    (b) Write the symbols of constituent elements and their valencies.

    (c) The positive and negative charges must balance each other and the overall structure must be neutral.

    (d) Then criss-cross their charges or valencies to get the formula.

    Right Option : B
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    Question : 2

    What is the formula of calcium oxide ?

    Right Option : A
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    Explanation
    Question : 3

    The combining elements in a molecule of carbon dioxide are ____________

    Right Option : C
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    Explanation
     
     


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