Writing formulae

• Chemistry
• Secondary Education

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Topic 6 - Formulae and Equations

Formulae of Compounds

10 November 2025

How do you feel today?

😒🙁😐🙂😃

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• I will know how to write the formulae of ionic and covalent compounds.
• I will understand why models and diagrams are important in writing the formulae of compounds.

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Are these two the same?

Cite one similarity and one difference 

between the two substances.

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How do you write the formulae of ionic compounds with ions NOT from Groups I-VII?

Valencies of ions not from I-VII

• Silver ion (Ag⁺ )                      +1   
• Zinc ion (Zn²⁺ )                       +2 
• Copper (I) ion  (Cu⁺ )             +1
• Copper (II) ion (Cu²⁺ )           +2
• Iron (II) ion  (Fe²⁺ )                +2
• Iron (III) ion  (Fe³⁺ )               +3
• Lead (II) ion (Pb²⁺ )                +2
• Lead (IV) ion (Pb⁴⁺ )              +4

Examples:

            copper (II) chloride         iron (III) chloride

Symbol:

Valency:

Formulae:

TEMPLATE

How do you write the formulae of ionic compounds with ions NOT from Groups I-VII?

Valencies of ions not from I-VII

• Silver ion (Ag⁺ )                      +1   
• Zinc ion (Zn²⁺ )                       +2 
• Copper (I) ion  (Cu⁺ )             +1
• Copper (II) ion (Cu²⁺ )           +2
• Iron (II) ion  (Fe²⁺ )                +2
• Iron (III) ion  (Fe³⁺ )               +3
• Lead (II) ion (Pb²⁺ )                +2
• Lead (IV) ion (Pb⁴⁺ )              +4

Examples:

            copper (II) chloride         iron (III) chloride

Symbol:

Valency:

Formulae:

1. Use the name to identify the atoms present.
2. Write the valency for each.
3. Swap the valencies. 
4. Simplify if they will both divide by the same number.

TEMPLATE

How do you write the formulae of ionic compounds with ions NOT from Groups I-VII?

Valencies of ions not from I-VII

• Silver ion (Ag⁺ )                      +1   
• Zinc ion (Zn²⁺ )                       +2 
• Copper (I) ion  (Cu⁺ )             +1
• Copper (II) ion (Cu²⁺ )           +2
• Iron (II) ion  (Fe²⁺ )                +2
• Iron (III) ion  (Fe³⁺ )               +3
• Lead (II) ion (Pb²⁺ )                +2
• Lead (IV) ion (Pb⁴⁺ )              +4

Examples:

            copper (II) chloride         iron (III) chloride

Symbol:

Valency:

Formulae:

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Work in groups: Solve the puzzle by determining the correct formulae for the given compounds.

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Will you follow the same method in writing the formulae of covalent compounds?

Example:

            a molecule of carbon and oxygen

Symbol:

Valency:

Formulae:

1. Use the name to identify the atoms present.
2. Write the valency for each.
3. Swap the valencies. 
4. Simplify if they will both divide by the same number.

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What if you are given these?

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Work individually: 

Do Activity 5 of your LAP sheets.

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• I will know how to write the formulae of ionic and covalent compounds.
• I will understand why models and diagrams are important in writing the formulae of compounds.

How well did you participate 

in the lesson today?

05

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Presents a new problem or scenario that requires students to apply their knowledge. For instance, after studying ecosystems, the teacher might ask students to explore the effects of an oil spill.

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Assesses student comprehension through a worksheet, quiz, a lab report, or a concluding class discussion.

How well did you enjoy the lesson today?

05

sample

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• I will know how to write the formulae of ionic and covalent compounds.
• I will understand why models and diagrams are important in writing the formulae of compounds.
• I will be able to write the molecular and empirical formulae of compounds.