Fundamentals of Chemistry: Atoms, Reactions, and Laws

Posted on Dec 18, 2024 in Chemistry

**1. The Atom**

  • Structure:
    • Protons (positive charge) in the nucleus.
    • Neutrons (neutral) in the nucleus.
    • Electrons (negative charge) in orbitals around the nucleus.
  • Atomic Number (Z): Number of protons in an atom.
  • Mass Number (A): Total number of protons and neutrons.
  • Isotopes: Atoms of the same element with different numbers of neutrons.

**2. The Periodic Table**

  • Groups (columns): Elements in the same group have similar properties.
  • Periods (rows): Properties change across a period.
  • Key Groups:
    • Group 1: Alkali Metals (e.g., Na, K).
    • Group 2: Alkaline Earth Metals (e.g., Mg, Ca).
    • Group 17: Halogens (e.g., F, Cl).
    • Group 18: Noble Gases (e.g., He, Ne).

**3. Chemical Bonds**

  • Ionic Bond: Electrostatic attraction between positively and negatively charged ions (e.g., NaCl).
    • Formed between metals and non-metals.
    • Electrons are transferred from metal to non-metal.
  • Covalent Bond: Electrons are shared between two non-metals (e.g., H₂O, CO₂).
    • Polar Covalent Bond: Electrons shared unevenly (e.g., H₂O).
    • Nonpolar Covalent Bond: Electrons shared equally (e.g., O₂).
  • Metallic Bond: Attraction between metal cations and free-moving valence electrons (e.g., in metals like Cu, Fe).

**4. Chemical Reactions**

  • Reactants → Products
  • Types of Reactions:
    • Synthesis (Combination): A + B → AB (e.g., 2H₂ + O₂ → 2H₂O)
    • Decomposition: AB → A + B (e.g., 2H₂O → 2H₂ + O₂)
    • Single Displacement: A + BC → AC + B (e.g., Zn + 2HCl → ZnCl₂ + H₂)
    • Double Displacement: AB + CD → AD + CB (e.g., NaCl + AgNO₃ → NaNO₃ + AgCl)
    • Combustion: Hydrocarbon + O₂ → CO₂ + H₂O (e.g., CH₄ + 2O₂ → CO₂ + 2H₂O)

**5. Balancing Chemical Equations**

  • Law of Conservation of Mass: Mass is neither created nor destroyed.
  • Steps for Balancing:
    1. Write the unbalanced equation.
    2. Count atoms of each element on both sides.
    3. Balance elements, starting with the most complex.
    4. Use coefficients to balance atoms.
    5. Check the balance after adjustment.

**6. Moles and Stoichiometry**

  • Mole Concept:
    • 1 mole = 6.022 × 10²³ particles (Avogadro’s number).
    • 1 mole of any substance = its molar mass in grams.
    • Molar Mass: The mass of 1 mole of a substance (g/mol).
  • Stoichiometry Steps:
    1. Write and balance the chemical equation.
    2. Convert the given substance (grams, moles) into moles.
    3. Use the mole ratio from the balanced equation to find moles of the desired substance.
    4. Convert moles back to grams or volume as needed.

**7. Acids and Bases**

  • Acids: Substances that release H⁺ ions in water (e.g., HCl, H₂SO₄).

    • Properties: Sour taste, turn blue litmus paper red, conduct electricity.
    • pH < 7.

  • Bases: Substances that release OH⁻ ions in water (e.g., NaOH, NH₃).

    • Properties: Bitter taste, slippery feel, turn red litmus paper blue, conduct electricity.
    • pH > 7.

  • pH Scale:

    • pH = 7: Neutral (pure water).
    • pH < 7: Acidic.
    • pH > 7: Basic (alkaline).

  • Neutralization Reaction:

    • Acid + Base → Salt + Water (e.g., HCl + NaOH → NaCl + H₂O).

**8. Gas Laws**

  • Boyle’s Law (P₁V₁ = P₂V₂): Pressure and volume are inversely related (at constant temperature).
  • Charles’ Law (V₁/T₁ = V₂/T₂): Volume and temperature are directly related (at constant pressure).
  • Ideal Gas Law: PV = nRT
    • P = Pressure (atm or Pa), V = Volume (L or m³), n = Moles of gas, R = Ideal gas constant (8.31 J/mol·K), T = Temperature (Kelvin).

**9. Solutions**

  • Solvent: Substance doing the dissolving (e.g., water).

  • Solute: Substance being dissolved (e.g., salt or sugar).

  • Concentration: Amount of solute in a given volume of solvent (e.g., mol/L or Molarity).

  • Solubility: The maximum amount of solute that can dissolve in a solvent at a given temperature.

    • Factors affecting solubility: Temperature, pressure (for gases), stirring.

**10. Periodic Trends**

  • Atomic Radius: Distance from the nucleus to the outermost electron.

    • Increases down a group, decreases across a period.

  • Ionization Energy: Energy needed to remove an electron from an atom.

    • Decreases down a group, increases across a period.

  • Electronegativity: Tendency of an atom to attract electrons in a bond.

    • Decreases down a group, increases across a period.

**11. Important Formulas**

  • Density: Density = Mass/Volume
  • Concentration (M): Moles of Solute/Volume of Solution (L)
  • Molar Mass: Mass/Moles
  • Ideal Gas Law: PV = nRT
  • Dilution Formula: C₁V₁ = C₂V₂ (Concentration and volume before and after dilution)

**12. Important Safety Tips**

  • Always wear safety goggles and gloves.
  • Work in a well-ventilated area.
  • Know the locations of fire extinguishers, eyewash stations, and first-aid kits.
  • Dispose of chemicals properly.