Chemistry Exam Notes

Atomic Structure

• Atoms have a positively charged nucleus (protons and neutrons) surrounded by negatively charged electrons in electron shells.
• The number of protons determines the element's atomic number.

Electron Configuration

• Represents electron arrangement in shells (e.g., Oxygen: 2,6).

Ions and Ionic Compounds

• Ions are charged atoms formed by electron gain (anions, negative) or loss (cations, positive).
• Ionic bonding: electrostatic attraction between ions (metal + non-metal).
• Ionic compounds: formed by ionic bonds.
• To write formulas, drop signs, cancel numbers if possible, and swap remaining numbers.

Types of Chemical Reactions

• Synthesis: A + B → AB
• Decomposition: AB → A + B
• Combustion: fuel + oxidant → heat + light (often $CO<em>2$ and $H</em>2O$)
• Neutralisation: acid + base → salt + water.
  • Strong acid + strong base -> neutral solution (pH 7)
  • Strong acid + weak base -> acidic solution (pH < 7)
  • Weak acid + strong base -> basic solution (pH > 7)
  • Weak acid + weak base -> close to neutral
• Precipitation: AB + CD → AD + CB (aqueous + aqueous → solid + aqueous).

Balancing Chemical Equations

• Equalize the number of atoms for each element on both sides by adjusting coefficients.

Predicting Products

• Synthesis: one product.
• Decomposition: two or more products.
• Combustion: carbon dioxide and water.
• Neutralisation: salt and water.
• Precipitation: solid (precipitate) and aqueous solution.

Factors Affecting Reaction Rate

• Temperature: increase rate with higher temperature (more energy).
• Concentration: increase rate with higher concentration (more collisions).
• Surface Area: increase rate with larger surface area (more exposure).
• Catalysts: increase rate by lowering activation energy; do not affect product amount.

Metals

• Alkali Metals: reactive, soft, low melting points, +1 ions, reactivity increases down the group.
• Alkaline Earth Metals: reactive, harder, higher melting points, +2 ions, reactivity increases down the group.
• Transition Metals: good conductors, high melting points, hard, dense, colored compounds, multiple ions, catalysts.

Periodic Table

• Atomic Number: number of protons.
• Mass Number: protons + neutrons.
• Electron Configuration: arrangement of electrons (e.g. 2,8,8,1).

Ions and Ionic Formulas

• Use ion charges to construct formulas with correct ratios.

Balanced Equations

• Write formulas, then balance by adjusting coefficients.
• Example: $Mg + 2HCl → MgCl<em>2 + H</em>2$

Determining Reaction Type

• Synthesis: A + B → AB
• Decomposition: AB → A + B
• Single Replacement: A + BC → AC + B
• Double Replacement: AB + CD → AD + CB
• Combustion: Fuel + $O<em>2$ → $CO</em>2$ + $H_2O$
• Precipitation: Two aqueous solutions form a solid.

Conservation of Mass

• Mass is neither created nor destroyed.
• Reactant mass = product mass.
• Example: 4g Hydrogen + 32g Oxygen → 36g Water

Factors Influencing Reaction Rate

• Temperature, surface area, catalysts, concentration. (Refer to slides 15-18).