SS1: CHEMISTRY – 1ST TERM Symbols, Formulae & Oxidation Number | Week 7 Rules for Writing Chemical Formula of Compounds

Lesson 7, Topic 6

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Rules for Writing Chemical Formula of Compounds

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Rules for Writing Chemical Formula of Compounds

1. Write down the symbol of elements or radicals.

2. Write the Oxidation numbers above and to the right of the symbol or radical

3. Now write the symbols again, reversing the Oxidation numbers and writing the numbers (but not 1) below and to the right of the symbol. Omit the signs.

Let us apply these rules in writing the Chemical formula of sodium tetraoxosulphate (IV)

Rule I	Na	SO₄
Rule II	Na⁺	SO₄^2-
Rule III	Na₂	SO₄

= Na₂SO₄

Example 7.6.1:

Write down the molecular formula of the following:

1. Sodium trioxonitrate (V)
2. Iron (III) Chloride
3. Calcium Oxide
4. Potassium tetraoxosulphate (VI)

Solution:

1. Sodium trioxonitrate (V)

Rule I	Na	NO₃
Rule II	Na⁺ \( \scriptsize \searrow \)	\( \scriptsize \swarrow\) NO₃^–
Rule III	Na	NO₃

= NaNO₃

2. Iron (III) Chloride

Rule I	Fe	Cl
Rule II	Fe³⁺\( \scriptsize \searrow \)	\( \scriptsize \swarrow\)Cl^–
Rule III	Fe	Cl₃

= FeCl₃

3. Calcium Oxide

Rule I	Ca	O
Rule II	Ca\( \scriptsize \searrow \)	\( \scriptsize \swarrow\)O^–
Rule III	Ca	O

= CaO

4. Potassium tetraoxosulphate (VI)

Rule I	K	SO₄
Rule II	K⁺\( \scriptsize \searrow \)	\( \scriptsize \swarrow\)SO₄^2-
Rule III	K₂	SO₄

= K₂SO₄

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Babe

2 years ago

Thank you ,I appreciate
You have really helped me

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Rules for Writing Chemical Formula of Compounds

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Example 7.6.1: