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Lewis Structures: Flashcards

Revise valence-electron counting, the octet rule, multiple bonds, formal charge and resonance.

10 cardsIntermediate

10 cards

  1. Question
    In a Lewis structure, what does a line between two atoms represent?
    Answer

    A shared pair of electrons (a single covalent bond).

  2. Question
    What is a lone pair?
    Answer

    A pair of valence electrons on one atom that is not shared in a bond.

  3. Question
    What is the octet rule?
    Answer

    Atoms tend to bond until they have 8 electrons in their outer shell (hydrogen: 2).

  4. Question
    How many valence electrons are in COX3X2−\ce{CO3^2-}?
    Answer

    4 + 3 × 6 + 2 = 24

  5. Question
    How many valence electrons are in NHX4X+\ce{NH4+}?
    Answer

    5 + 4 × 1 − 1 = 8

  6. Question
    Which atom usually goes in the centre of a Lewis structure?
    Answer

    The least electronegative atom, never hydrogen.

  7. Question
    What is the formula for formal charge?
    Answer

    Valence electrons − lone-pair electrons − ½ × bonding electrons

  8. Question
    What is resonance?
    Answer

    When two or more valid Lewis structures differ only in electron placement; the real species is an average (hybrid) of them.

  9. Question
    Draw the Lewis structure of NX2\ce{N2} in words.
    Answer

    N≡N, a triple bond, with one lone pair on each nitrogen (10 valence electrons).

  10. Question
    Give an example of a molecule with an incomplete octet.
    Answer

    BFX3\ce{BF3}: boron has only 6 electrons around it.