SC2a: Intramolecular and Intermolecular Forces

SC2a: Intramolecular and Intermolecular Forces

Intramolecular Forces:

  • Covalent Bonds: Atoms share electrons. For instance, in a water molecule (H₂O), each hydrogen atom shares an electron with the oxygen atom.

  • Ionic Bonds: Atoms transfer electrons. For example, in sodium chloride (NaCl), sodium donates an electron to chlorine, resulting in positive (Na⁺) and negative (Cl⁻) ions.

  • Metallic Bonds: Electrons flow freely among a lattice of metal cations. This is why metals like copper (Cu) are good conductors of electricity.

Intermolecular Forces:

  • London Dispersion Forces: Weakest intermolecular forces, present in all molecules, stronger in larger atoms/molecules. Example: Noble gases like argon (Ar) exhibit these forces.

  • Dipole-Dipole Interactions: Occur in polar molecules, such as hydrogen chloride (HCl), where the positive end of one molecule attracts the negative end of another.

  • Hydrogen Bonds: Strong interactions in molecules where H is bonded to N, O, or F. Water (H₂O) molecules form hydrogen bonds, giving water its unique properties like high boiling point.

SC2b: Physical Properties and Forces

  • Melting Point and Boiling Point:

    • Water (H₂O): High boiling point for its size due to hydrogen bonding.

    • Methane (CH₄): Lower boiling point because it only has London dispersion forces.

  • Solubility:

    • Polar substances (like salt, NaCl) dissolve well in polar solvents (like water) due to strong ion-dipole interactions.

    • Nonpolar substances (like oil) do not dissolve in water because there are no strong interactions to overcome the cohesive forces within the water.

SC2c: Electrical Conductivity of Metals

  • Metals like Copper (Cu): Excellent conductors because of their "sea of electrons," which allows electrons to move freely and carry electrical current.

  • Example: Copper wires are used in electrical circuits because they efficiently conduct electricity.

SC2d: Types of Bonding

  • Ionic Bonding:

    • Example: Sodium chloride (NaCl), where sodium (metal) transfers an electron to chlorine (nonmetal).

  • Polar Covalent Bonding:

    • Example: Water (H₂O), where oxygen is more electronegative than hydrogen, leading to unequal sharing of electrons.

  • Nonpolar Covalent Bonding:

    • Example: Oxygen gas (O₂), where electrons are shared equally between the two oxygen atoms.

  • Electronegativity:

    • Example: In HCl, chlorine is more electronegative than hydrogen, creating a polar covalent bond.

  • Lewis Diagrams:

    • Example: For H₂O, the Lewis diagram shows two hydrogen atoms sharing electrons with one oxygen atom, represented as H–O–H with pairs of dots around the O indicating lone pairs.

SC2e: IUPAC Nomenclature

  • Binary Ionic Compounds:

    • Example: NaCl is named sodium chloride.

  • Ternary Ionic Compounds:

    • Example: NaNO₃ is named sodium nitrate.

  • Ionic Compounds with Transition Metals:

    • Example: FeCl₂ is named iron(II) chloride, indicating iron's +2 oxidation state.

  • Inorganic Covalent Compounds:

    • Example: CO₂ is named carbon dioxide, where "di-" indicates two oxygen atoms.

  • Acidic Compounds:

    • Example: HCl (in solution) is called hydrochloric acid.

SC2f: Writing Chemical Formulas

  • Binary Ionic Compounds:

    • Example: Magnesium chloride is MgCl₂ because magnesium is Mg²⁺ and chlorine is Cl⁻, requiring two Cl⁻ ions to balance.

  • Ternary Ionic Compounds:

    • Example: Calcium nitrate is Ca(NO₃)₂, with Ca²⁺ balancing two NO₃⁻ ions.

  • Ionic Compounds Involving Transition Metals:

    • Example: Copper(II) sulfate is CuSO₄, indicating copper's +2 oxidation state.

  • Inorganic Covalent Compounds:

    • Example: Dinitrogen tetroxide is N₂O₄.

  • Acidic Compounds:

    • Example: Sulfuric acid (H₂SO₄) is composed of H⁺ ions and sulfate ions (SO₄²⁻).