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Organic Chemistry: Bonding and Atomic Structure

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  • What defines an organic molecule?
    An organic molecule contains both carbon and hydrogen. A molecule with only carbon and hydrogen is called a hydrocarbon.
  • What is the atomic number of an atom?
    The atomic number equals the number of protons in the nucleus.
  • How is the mass number of an atom calculated?
    Mass number = number of protons + number of neutrons.
  • What are isotopes?
    Atoms with the same atomic number but different numbers of neutrons.
  • What is an atomic orbital?
    A region of space within a shell that can hold a pair of electrons with opposite spins.
  • What are cations and anions?
    Cations are positively charged atoms (fewer electrons than protons). Anions are negatively charged atoms (more electrons than protons).
  • State the Aufbau Principle.
    Electrons fill orbitals in order of increasing energy.
  • State the Pauli Exclusion Principle.
    A maximum of two electrons can occupy each orbital, with opposite spins.
  • State Hund's Rule.
    Electrons fill orbitals of equal energy singly before pairing up.
  • What does the Heisenberg Uncertainty Principle state?
    We cannot simultaneously know an electron's exact position and momentum.
  • What is a wave function in quantum mechanics?
    An equation describing the energy state of an electron; its square gives the probability of finding the electron.
  • What is an atomic orbital shape?
    A 3D plot of the wave function showing regions where the electron is likely to be found.
  • What happens when atomic orbitals overlap constructively?
    They form bonding molecular orbitals with shared electron density.
  • What is the Linear Combination of Atomic Orbitals (LCAO)?
    A model using addition and subtraction of atomic orbitals to predict molecular orbital energies.
  • Define sigma (σ) and pi (π) bonds.
    σ bonds form by head-on overlap of orbitals; π bonds form by side-on overlap of p orbitals.
  • What is the octet rule?
    Atoms tend to gain, lose, or share electrons to achieve a noble gas configuration of 8 valence electrons.
  • How many octet electrons do first-row elements like H, He, and Li prefer?
    They prefer to have 2 octet electrons.
  • What are formal charges?
    Formal charge = Group number - (number of valence electrons + 1/2 bonding electrons). It helps determine the most stable Lewis structure.
  • What is the bondline (skeletal) structure convention?
    Carbon atoms are implied at line ends and bends; hydrogens on carbons are implied to fill octets; heteroatoms and hydrogens on them are drawn explicitly.
  • How do you determine the number of implied hydrogens on a carbon in bondline structures?
    Count the bonds to carbon; implied hydrogens = 4 minus the number of bonds.