Chemical Reactions and Equations

Chemical Equations

• Basic word equation: Hydrogen + Oxygen → Water
• Chemical equation with state symbols:
  • Unbalanced: $H<em>2 + O</em>2 → H_2O$
  • Balanced: $2H<em>2 + O</em>2 → 2H_2O$

Ionic Equations

• Focus on ionic equations, half equations, and redox reactions.

Example: Magnesium and Zinc Sulfate

• Reaction: Magnesium (solid) + Zinc Sulfate (aqueous) → Magnesium Sulfate (aqueous) + Zinc (solid)
  • $Mg(s) + ZnSO<em>4(aq) → MgSO</em>4(aq) + Zn(s)$
• This is a displacement reaction.

Displacement Reaction

• A more reactive element displaces a less reactive element.
  • Magnesium is more reactive than zinc, hence it displaces zinc from zinc sulfate.
• If the reverse occurs (Zinc + Magnesium Sulfate), no reaction happens because zinc is less reactive than magnesium.
  • $Zn(s) + MgSO_4(aq) → No Reaction$

State Symbols

• s = solid
• l = liquid
• g = gas
• aq = aqueous (dissolved in water)
  • Aqueous solutions contain ions.
  • Example: $ZnSO<em>4(aq)$ consists of $Zn^{2+}$ and $SO</em>4^{2-}$ ions floating freely in water.

Ionic Equation Breakdown

• $Mg(s) + ZnSO<em>4(aq) → MgSO</em>4(aq) + Zn(s)$
• $Mg(s) + Zn^{2+}(aq) + SO<em>4^{2-}(aq) → Mg^{2+}(aq) + SO</em>4^{2-}(aq) + Zn(s)$
• Spectator ions: Ions that do not participate in the reaction (e.g., $SO<em>4^{2-}$, which remains $SO</em>4^{2-}$).
• Ionic Equation: Includes only the reacting species.
  • $Mg(s) + Zn^{2+}(aq) → Mg^{2+}(aq) + Zn(s)$

Half Equations

• Breaking down the ionic equation into oxidation and reduction half-reactions.

Magnesium Half-Equation

• $Mg → Mg^{2+} + 2e^-$
• Magnesium loses two electrons to become $Mg^{2+}$.

Zinc Half-Equation

• $Zn^{2+} + 2e^- → Zn$
• Zinc gains two electrons to become $Zn$.

Oxidation and Reduction (Redox)

• Oxidation: Loss of electrons.
  • $Mg → Mg^{2+} + 2e^-$ (Magnesium is oxidized)
• Reduction: Gain of electrons.
  • $Zn^{2+} + 2e^- → Zn$ (Zinc is reduced)
• Redox Reaction: A reaction where both oxidation and reduction occur simultaneously.

Chemical Formulas

Determining Chemical Formulas Using the Periodic Table

• Elements in the same group have similar ionic charges.
  • Group 1 elements form +1 ions.
  • Group 2 elements form +2 ions.
  • Group 3 elements form +3 ions.
  • Group 5 elements form -3 ions.
  • Group 6 elements form -2 ions.
  • Group 7 elements form -1 ions.

Examples of Ions

• Oxygen (Group 6): $O^{2-}$
• Nitrogen (Group 5): $N^{3-}$
• Lithium (Group 1): $Li^{+1}$
• Sodium (Group 1): $Na^{+1}$
• Magnesium (Group 2): $Mg^{2+}$
• Calcium (Group 2): $Ca^{2+}$

Swap and Drop Method

• Used to determine chemical formulas.

Procedure

1. Identify the ions and their charges.
2. Swap the magnitudes of the charges.
3. Drop the charges.

Example: Magnesium Chloride

• Magnesium: $Mg^{2+}$
• Chloride: $Cl^{-1}$
• Swap and Drop:
  • $Mg<em>1Cl</em>2$
• Chemical Formula: $MgCl_2$

Practice Examples

• Sodium Chloride: NaCl
• Magnesium Bromide: $MgBr_2$
• Calcium Fluoride: $CaF_2$
• Aluminum Oxide: $Al<em>2O</em>3$
• Magnesium Oxide: MgO

Transition Metals and Roman Numerals

• Transition metals can have multiple oxidation states (variable charges).
• Roman numerals indicate the charge of the transition metal ion.

Example: Iron (III) Oxide

• Iron (III): $Fe^{3+}$
• Oxide: $O^{2-}$
• Chemical Formula: $Fe<em>2O</em>3$

Example: Cobalt (II) Chloride

• Cobalt (II): $Co^{2+}$
• Chloride: $Cl^{-1}$
• Chemical Formula: $CoCl_2$

Common Ions

• Iron (II): $Fe^{2+}$
• Iron (III): $Fe^{3+}$
• Sulfate: $SO_4^{2-}$
• Sulfide: $S^{2-}$
• Carbonate: $CO_3^{2-}$
• Nitrate: $NO_3^{-}$
• Hydroxide: $OH^{-}$

Chemical Formula Examples with Polyatomic Ions

• Aluminum Hydroxide: $Al(OH)_3$
• Calcium Nitrate: $Ca(NO<em>3)</em>2$
• Sodium Nitrate: $NaNO_3$

Importance of Fundamentals

• Understanding chemical formulas and equations is crucial for success in chemistry.
• Practice with examples to build confidence.

Splitting Substances in Equations

• $AgNO_3$ and $KCl$ are expected to be split into ions in aqueous solutions.

Applications

• Dentistry requires knowledge of chemical language (formulas and equations).