Chemistry Lesson Note On Chemical Symbols, Formulae, and Equations – Writing Symbols, Formulae, Balancing Equations

Topic: Chemical Symbols, Formulae, and Equations – Writing Symbols, Formulae, Balancing Equations

Class: SS1

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Specific Objectives

By the end of the lesson, students should be able to:

1. Identify and write correct chemical symbols for elements.
2. Write chemical formulae for simple compounds.
3. Interpret and write balanced chemical equations.
4. Apply the law of conservation of mass to balance chemical equations.

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Instructional Materials

• Periodic table chart
• Flashcards with element symbols
• Sample chemical compounds and equations
• Whiteboard and markers
• Worksheets for practice

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Lesson Content

Step 1: Chemical Symbols

Chemical symbols are abbreviations used to represent elements.

• They are usually derived from the English or Latin names of elements.
• Examples:
  • H – Hydrogen
  • O – Oxygen
  • Na – Sodium (from Latin "Natrium")
  • Fe – Iron (from Latin "Ferrum")

Note: The first letter is always capitalized. If there is a second letter, it is lowercase.

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Step 2: Writing Chemical Formulae

Chemical formulae represent the composition of compounds using symbols and numbers.

• Valency is the combining power of an element.
• To write formulae, criss-cross the valencies of combining elements.

Examples:

• Sodium chloride: Na¹⁺ + Cl¹⁻ → NaCl
• Calcium chloride: Ca²⁺ + Cl¹⁻ → CaCl₂
• Aluminum oxide: Al³⁺ + O²⁻ → Al₂O₃

Types of compounds:

• Binary compounds: Contain two elements (e.g., HCl, Na₂O)
• Ternary compounds: Contain three elements, often including oxygen (e.g., H₂SO₄, NaNO₃)

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Step 3: Writing and Balancing Chemical Equations

A chemical equation represents a chemical reaction using formulas.

• Reactants → Products

Unbalanced equation:

\text{H₂ + O₂ → H₂O}

Balanced equation:

2H₂ + O₂ → 2H₂O

Balancing ensures the law of conservation of mass is obeyed: total number of atoms on both sides must be equal.

Steps to balance equations:

1. Write correct formulas for all reactants and products.
2. Count the number of atoms of each element.
3. Use coefficients to balance atoms.
4. Recheck to confirm equality on both sides.

Example 1:

Na + Cl₂ → NaCl  
\Rightarrow 2Na + Cl₂ → 2NaCl

Example 2:

Fe + O₂ → Fe₂O₃  
\Rightarrow 4Fe + 3O₂ → 2Fe₂O₃

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Evaluation

1. What is a chemical symbol? Give five examples.
2. Write the formula for:
   a) Magnesium oxide
   b) Sodium carbonate
   c) Calcium nitrate
3. Write and balance the following equations:
   a) H₂ + O₂ → H₂O
   b) Fe + Cl₂ → FeCl₃
4. State the law that governs the balancing of chemical equations.

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Homework

1. Write chemical symbols for the following elements: Copper, Lead, Potassium, Nitrogen, and Zinc.
2. Write the correct formula for the following compounds:
   a) Potassium permanganate
   b) Aluminium sulphate
   c) Sodium hydroxide
3. Balance the following chemical equations:
   a) C + O₂ → CO₂
   b) N₂ + H₂ → NH₃
   c) Ca + HCl → CaCl₂ + H₂

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Conclusion

Understanding symbols, formulae, and chemical equations is essential in studying chemical reactions. Balancing equations ensures the law of conservation of mass is upheld and helps predict the outcome of chemical changes.