Chemical Formulas and Reactions

Elemental Symbols and Formulas

• Examples of Element Symbols:

  • Sodium (Na)
  • Chlorine (Cl)

• Example of a Compound Formula:

  • Sodium Chloride (NaCl)

Molecular Formula

• Defined as the actual number of atoms of each element in a molecule.
• Example: Water has the molecular formula $H_2O$.

Deduction from Models

• Count atoms of each element in models/diagrams to deduce formulas.
• Example: 6 Hydrogen and 2 Carbon atoms give $C<em>2H</em>6$ (ethane).

Word and Symbol Equations

• State Symbols:

  • (s): solid
  • (l): liquid
  • (g): gas
  • (aq): aqueous

• Example of a Word Equation:

  • Hydrochloric acid + Sodium hydroxide -> Sodium chloride + Water

• Example of a Balanced Chemical Equation:

  • HCl(aq) + NaOH(aq) -> NaCl(aq) + H_2O(l).

Empirical Formula

• Simplest whole number ratio of atoms in a compound.
• Example: For $C<em>2H</em>6$, the empirical formula is $CH_3$.

Ionic Compounds

• To deduce formulas: identify ions and their charges.
• Ionic compounds have an overall charge of zero.
• Examples:
  • Sodium Chloride: Na^+ + Cl^- -> NaCl
  • Magnesium Chloride: Two $Cl^-$ needed for one $Mg^{2+}$, so $MgCl_2$.

Constructing Symbol Equations

• Equation Format: reactants (+
  reactants) -> products (+
  products)
• Ensure balance of atoms and charges on both sides.
• Include state symbols in equations.

Example of Balancing a Reaction

• Given: Magnesium + Oxygen -> Magnesium oxide.
• Step 1: Identify symbols:
  • Magnesium: $Mg$
  • Oxygen: $O_2$
  • Magnesium Oxide: $MgO$
• Step 2: Unbalanced equation: Mg + O_2 -> MgO
  • Balanced: 2Mg + O_2 -> 2MgO
• Step 3: Add state symbols: 2Mg (s) + O_2 (g) -> 2MgO (s)