Study Notes
Understanding formulae is essential for writing balanced chemical equations and determining the correct amounts of reactants and products in a reaction.
- Ionic Compounds — compounds made of positive and negative ions held together by ionic bonds. Example: Sodium chloride (NaCl) is formed from Na+ and Cl- ions.
- Formula of Ionic Compounds — determined by combining cations and anions in a ratio that results in a neutral charge. Example: Na+ and Cl- combine to form NaCl.
- Constructing Equations — involves writing balanced chemical equations and replacing neutral compounds with their ions. Example: Na + Cl2 → Na+ + Cl-.
- Balancing Chemical Equations — ensuring the number of atoms of each element is equal on both sides of the equation. Example: 2H2 + O2 → 2H2O.
Exam Tips
Key Definitions to Remember
- Ionic compounds are made of cations and anions held by ionic bonds.
- The formula of ionic compounds is neutral, with balanced charges.
Common Confusions
- Forgetting to balance charges when writing ionic formulas.
- Mixing up coefficients and subscripts in chemical equations.
Typical Exam Questions
- How do you write the formula for sodium chloride? Combine Na+ and Cl- to form NaCl.
- What is the ionic equation for sodium reacting with chlorine? Na + Cl2 → Na+ + Cl-.
- How do you balance the equation H2 + O2 → H2O? 2H2 + O2 → 2H2O.
What Examiners Usually Test
- Ability to write and balance chemical equations.
- Understanding of ionic compounds and their formulas.