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Equation Writing

Equation Writing. Types of Ions. Positive ions (cations) Negative ions (anions) Simple ions Polyatomic ions. Cations. Cations. Anion. Simple ions. formed from single atoms e.g. Mg ion some elements form more than one type of cation.

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Equation Writing

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  1. Equation Writing

  2. Types of Ions • Positive ions (cations) • Negative ions (anions) • Simple ions • Polyatomic ions

  3. Cations

  4. Cations

  5. Anion

  6. Simple ions • formed from single atoms e.g. Mg ion • some elements form more than one type of cation. Roman numerals are used to indicate the number of charges. e.g. iron forms iron (II) & iron (III) ions. • Roman numerals are not needed when the metal forms only 1 type of ion.

  7. Polyatomic ions • consist of more than one type of atom e.g. ammonium ion (NH4+) - 1 N atom & 4 H atoms has a charge of 1+ because total no. of protons in NH4+ ion is one more than the total no. of electrons.

  8. Formulae of Ionic Compounds • negative and positive charges must be balanced • E.g. KF each F- ion must have one K+ ion • E.g. MgF2 each Mg2+ ion must have two F- ions

  9. Chemical formula of copper (II) hydroxide Ions present: Cu2+ OH- OH- --------------------- Total charge: 2+ 2- chemical formula: Cu(OH)2

  10. Naming Ionic Compounds • ammonium ion or metal ion is always written first in the formula and in the name • E.g. NaCl not ClNa sodium chloride not chloride sodium • E.g. NH4Cl not ClNH4 Ammonium chloride not chloride ammonium

  11. Naming Ionic Compounds • When there is more than one polyatomic ion in the compound, the ion is placed in brackets Correct: Cu(OH)2 Wrong: CuO2H2 Wrong: CuOH2

  12. Constructing Chemical Equations Sodium Reactive Dangerous Chlorine Poisonous Dangerous Sodium chloride Safe reactants product

  13. Constructing Chemical Equations • When an equation is written in words, it is called word equation. • When an equation is written with symbols and formulae, it is called chemical equation.

  14. Reaction between Oxygen and Hydrogen + Hydrogen molecule Oxygen molecule water

  15. + Reaction between Oxygen and Hydrogen Word equation: hydrogen + oxygen → water Using formulae: H2 + H2 + H2 + H2 + O2 + O2 → H2O + H2O + H2O + H2O 4H2 + 2O2 → 4H2O Chemical equation: 2H2 + O2 → 2H2O (simplest whole number ratio)

  16. Balancing Equations • All chemical equations must be balanced. • A balanced equation has the same number of atoms of each element on both sides of the equation.

  17. Balancing Equations 2H2 + O2 → 2H2O H atoms = 4 H atoms= 4 O atoms = 2 O atoms =2 • Number of atoms of reactants = Number of atoms of products.

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