Chemistry Notes: Atomic Structure, Periodic Table, Bonding, Hydrocarbons, and Energy in Reactions

Atomic Structure

• Lithium-7 Atom:
  • Diagram should include:
    • 3 protons
    • 4 neutrons
    • 3 electrons
• Electron Configuration of Argon (Ar):
  • $1s^22s^22p^63s^23p^6$

Periodic Table

• Element Identification:
  • Electron configuration: $[Kr] 5s^2 4d^{10} 5p^5$
  • Element: Iodine (I)
  • Position: Period 5, Group 17 (Halogens)
• Significance of s, p, d, and f Blocks:
  • s-block: Groups 1 and 2; filling of the s orbitals.
  • p-block: Groups 13 to 18; filling of the p orbitals.
  • d-block: Transition metals; filling of the d orbitals.
  • f-block: Lanthanides and actinides; filling of the f orbitals.

Bonding Between Atoms

• Ionic Bonding - Sulfur Ion:
  • Sulfur (S) gains 2 electrons to achieve a stable octet.
  • Charge: $-2$
  • Electron Configuration: $1s^22s^22p^63s^23p^6$
• Empirical Formula:
  • Aluminum (Al) and Chlorine (Cl) form $AlCl_3$

Hydrocarbons

• Combustion of Pentane ($C<em>5H</em>{12}$):
  • Balanced chemical equation:
    $C<em>5H</em>{12}(g) + 8O<em>2(g) \rightarrow 5CO</em>2(g) + 6H_2O(g)$
• Structural Formula and Name:
  • $C<em>6H</em>{14}$ with one alkene group.
    • One possible structure: Hexene

Structural Isomers

• Hydrocarbons with up to six carbon atoms and one alkene group:
  • Examples:
    • But-1-ene
    • But-2-ene
    • 2-methylpropene
    • Pent-1-ene
    • Pent-2-ene
    • 2-methylbut-1-ene
    • Hex-1-ene
    • Hex-2-ene
    • Hex-3-ene
    • Various other branched isomers

Energy in Reactions

• Thermochemistry:
  • $CH<em>4(g) + 2O</em>2(g) \rightarrow CO<em>2(g) + 2H</em>2O(g) + energy$
  • This reaction is exothermic because it releases energy.
• Potassium Chloride (KCl) dissolving in water:
  • Endothermic process overall
  • Requires energy to break ionic bonds in KCl lattice (endothermic).
  • Releases energy when $K^+$ and $Cl^-$ ions are solvated by water molecules (exothermic).
  • If the energy required to break the ionic bonds is greater than the energy released during solvation, the overall process is endothermic, and the solution cools down.

Calorimetry

• Temperature Change Calculation:
  • 50 g of water heated from 25°C to 45°C.
  • Temperature change: $\Delta T = 45°C - 25°C = 20°C$
• Reasons for Differences Between Experimental and Theoretical Enthalpy Changes:
  • Heat Loss: Heat may be lost to the surroundings (e.g., calorimeter not perfectly insulated), leading to a lower experimental value.
  • Incomplete Reaction: The reaction may not go to completion, or there might be side reactions occurring, resulting in a lower measured enthalpy change. Also some of the reactant could stick to the side of the container.