The Concept of Chemical Formula & Guidelines for writing Chemical Formulas of Simple Binary compounds through systematic approach.

Greetings Dear Science Teachers and Students! I am very happy to share with you once again a very important science concept that most of us find it very difficult. "The concept of Chemical formula, chemical equation, valency and formation of ions.

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Meaning of a chemical formula

A Chemical formula is a way of expressing or presenting chemical data about the proportion of atoms that constitute a particular chemical compounds, using single line of chemical element symbols, numbers and brackets. Examples of chemical formulas are Water = H₂O, Carbon (IV) Oxide = CO₂, Ammonia = NH₃, Glucose = C₆H₁₂C₆

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How to write chemical formula of binary compound

First of all, A Binary compound is a compound involving only two (2) elements. Examples of binary compounds are water, carbon (IV) oxide, Ammonia, Sodium chloride, Magnesium oxide and calcium chloride.

Guidelines...

1• write the chemical symbols involved in the binary compounds.

2• Indicate the charges or ions involved in the individual atoms forming the compound.

3• Change the charges into valency and write them as subscripts. Valency simply means the combining power of atoms. This appears to be the number of electrons that are gained or lost to atoms at the outermost shells.

4• Exchange the valencies. A common factor involved in the formula is dealt with or cancelled out.

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Work examples of chemical formulas of binary compounds using the above guidelines...

Write the chemical formula of the following Binary compounds:

1• Carbon IV Oxide

2• Water

3• Sodium chloride

4• Ammonia

5• Calcium Chloride

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Solution

• Carbon IV Oxide into symbols =

C + O

The second rule is to indicate the charges or ion formed ( either cation or anion with the number of charges lost of gain).

• Carbon ( C) has atomic/proton number of 6 and loses 4 electrons when the K-shell takes a maximum number of 2 electrons. This becomes _C+4. Oxygen (O) has 8 atomic/proton numbers and therefore gains 2 electrons for the L-shell to become fully filled. This becomes _O-2

This is shown as:

_C+4 + _O-2

• Representation or the formula as valence subscription:

C₄O₂

Here the common factor between 4 & 2 = 2. This means 2 divides 4 into 2 times and itself 1 time.

That is C₂O₁

• Exchange the valencies here:

This becomes:
C₁O₂

Note: C₁ is the same as "C"

So the formula becomes CO₂

Now the chemical formula for carbon IV Oxide is CO₂

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2• Following the same procedure in this work example 2,

The symbols of water is written as:

H + O

• Indicate the charges or ions involved as shown:

_H+1 + _O-2

• change the charges to valencies and write them as subscripts:

H₁O₂

• Exchange the valencies involved in the formula:
  H₂O₁

• Write the final formula as shown below:

H₂O

Now the chemical formula for Water is:

H₂O

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3• Chemical Formula for Sodium Chloride.

The symbols of Sodium Chloride is written as:

Na + Cl

• Indicate the charges or ions involved as shown:

_Na+1 + _Cl-1

• change the charges to valencies and write them as subscripts:

Na₁Cl₁

• Exchange the valencies involved in the formula:
  Na₁Cl₁

The final formula is written as
NaCl

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4•Chemical formula for Ammonia

The chemical symbols of Ammonia is written as:

N + H

• Indicate the charges or ions involved as shown:

_N-3 + _H+1

• change the charges to valencies and write them as subscripts:

N₃H₁

• Exchange the valencies involved in the formula:
  N₁H₃

The final formula is written as
NH₃

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5• The chemical formula for Calcium Chloride is:

Ca + Cl

• Indicate the charges or ions involved as shown:

_Ca+2 + _Cl+1

• change the charges to valencies and write them as subscripts:

Ca₂Cl₁

• Exchange the valencies involved in the formula:
  Ca₁Cl₂

The final formula is written as
CaCl₂

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I hope we had a very successful lesson of how to write chemical formula for simple Binary compounds. We will proceed to learn how to write chemical equation in our next lesson. Thanks for your attention and reading!

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