Lecture #2

  • RECITATION QUIZ HINT:

    • MAKE FLASHCARDS OF THE FUNCTIONAL GROUPS


    Follow the three rules for Lewis Dot Structures

    • (see last lecture)

Lewis Dot Structures:

  • Formal charge:

    • The charge on an atom in a molecule

    • Formal charge = (#ve^-) - (all unshared e^- + ½ all shared electrons)

  • H3O+

    • FC = 6 - (2+3) = +1

  • HCO3+

Functional Group:

  • Allows for the division of compounds into classes

  • Exhibit characteristics chemical reactions

  • Provides basis for naming molecules

Alcohol:

  • Hydroxyl: alcohol functional group

  • alcohol: entire molecule



    • 1° - primary

    • 2° - secondary

    • 3° - tertiary

Halides:

  • Halogen → functional

    • F: fluoride

    • Cl: Chloride

    • Br: Bromide

    • I: Iodide

  • 1°

  • 2°

  • 3°

Amines:

  • Amino: functional group

  • Amine: entire compound

  • Classification → how many carbons are attached directly to nitrogen

Aldehydes & Keytones

  • Carbonyl is the key functional group in both aldehydes and ketones

  • Aldehyde:

    • Carbonyl + hydrogen

  • Ketone:

    • Carbonyl + 2 carbons

Carboxylic Acid, Ester, Amide

  • Carboxylic acid:

    • Carboxyl + alcohol

  • Ester:

    • Carboxylic acid - H + Carbon

  • Amide:

    • Carbonyl + amine

Ether & Thiol

  • Ether

    • Think “either ror”

  • Thiol:

    • sulfur

Valence- shell Electron-pair repulsion theory

  • VSPER is based on the electrons in an atom’s valence shell

  • Remember:

    • electrons repel each other

    • the furthest they can be away from each other is 109.5° (tetrahedral)

    • Lone pairs take more space than bonding groups

  • Methane

    • Angles are less than 109.5°

Valence-shell electron-pair repulsion theory

  • Region of electron density around central atom: 4

    • Tetrahedral

    • 109.5°

  • Region of electron density around central atom: 3

    • trigonal planar

    • 120°

  • Region of electron density around central atom: 2

    • Linear

    • 180°

Polar and Nonpolar Molecules

  • Remember: This class is focused on “where are the electrons and why?”

  • Polar bonds: Unequal sharing of electrons

  • Nonpolar bonds: Equal sharing of electrons


  • Molecular dipole moment (mu): the vector sum of a molecule’s individual dipoles

    • → → (add)

    • ← → (subtract)

  • Vectors cancel out = non polar molecule

  • Vectors add = polar molecule


Molecular Orbital Theory

  • Allows us to better predict where an electron might be located

    • Quantum Mechanics: the branch of science that studies particles and their wave-like properties

      • Electrons can act as a particle and wave

    • Schrodinger’s equation: The spatial arrangement of where it is possible to find electrons

      • (wave functions — AKA — orbitals)


      • Node shown → no e- density

Molecular Orbital Theory (cont)


  • green - in phase (will never be the same color for clarity)

  • bottom left - d

  • bottom right - f

Combined VB & MO theory

  • Most scientists use this model

    • Other vocab:

      • Atomic orbitals

      • molecular orbitals

      • ground state

      • excited state

  • Rules:

    1. # of Atomic orbitals = # of molecular orbitals

    2. molecular orbitals are arranged in increasing energy

      1. see picture from phone

  • Valence bond theory:

    • The molecular model that theorizes that bonds are created by the overlap of orbitals on adjacent atoms

  • The main difference between MO and VB

    • MO: bonds (electrons) are delocalized across