Chemical Bonds and Lewis Structures
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Questions and Answers

What happens to the bond length as the number of bonds between two carbon atoms increases?

  • The bond length decreases as the bonds become stronger (correct)
  • The bond length increases due to less electron sharing
  • The bond length becomes unpredictable
  • The bond length remains the same regardless of the number of bonds

    • Which statement best describes a dative bond?

  • Dative bonds cannot involve lone pairs of electrons
  • The pair of shared electrons is supplied by one of the two bonded atoms (correct)
  • Dative bonds can only be formed between identical atoms
  • Both atoms contribute equally to the shared electrons

    • What characterizes a double bond between two atoms?

  • Sharing three pairs of electrons
  • Sharing one pair of electrons
  • Complete electron transfer from one atom to another
  • Sharing two pairs of electrons (correct)

    • Which of the following is true about triple bonds?

    <p>They occur when two atoms share three pairs of electrons</p> Signup and view all the answers

    Which condition is necessary for the formation of a dative bond?

    <p>The donor atom must have at least one lone pair of electrons</p> Signup and view all the answers

    What type of bond is formed between nitrogen and hydrogen in the ammonium ion?

    <p>Dative bond</p> Signup and view all the answers

    When drawing the Lewis structure for water, which atom is placed in the center?

    <p>Oxygen</p> Signup and view all the answers

    How many total valence electrons are present in methane (CH4)?

    <p>8</p> Signup and view all the answers

    Which is the first step in writing Lewis structures?

    <p>Count total number of valence electrons</p> Signup and view all the answers

    What is one of the requirements for a molecule or ion to have a resonance structure?

    <p>It must have multiple bonds</p> Signup and view all the answers

    Which pair of elements is often assigned as the central atom in a Lewis structure?

    <p>The least electronegative element</p> Signup and view all the answers

    Which statement is true about formal charges?

    <p>A formal negative charge can exist on a more electropositive atom.</p> Signup and view all the answers

    What shape should be expected for a molecule with the formula COCl2?

    <p>Trigonal planar</p> Signup and view all the answers

    Which of the following molecules can have an incomplete octet?

    <p>Boron trifluoride (BF3)</p> Signup and view all the answers

    In Lewis structures, what is typically true of polyatomic species?

    <p>They are usually clumped together</p> Signup and view all the answers

    Which of the following compounds can exhibit an expanded octet?

    <p>Sulfur hexafluoride (SF6)</p> Signup and view all the answers

    What action should be taken if a Lewis structure contains too many electrons?

    <p>Form double and triple bonds as needed</p> Signup and view all the answers

    What condition allows a molecule or ion to have a formal positive charge?

    <p>It must be on a more electropositive atom.</p> Signup and view all the answers

    Which of the following is an example of an odd electron species?

    <p>Nitric oxide (NO)</p> Signup and view all the answers

    In what case must a molecule have lone pair electrons?

    <p>To facilitate resonance structures</p> Signup and view all the answers

    Which of the following is a requirement for a molecule to have a resonance structure?

    <p>It must have at least one double bond</p> Signup and view all the answers

    What is the purpose of calculating formal charges in Lewis structures?

    <p>To find the most stable Lewis structure with charges closest to zero</p> Signup and view all the answers

    When constructing a Lewis structure, which atom type should typically be placed in the center?

    <p>The least electronegative atom</p> Signup and view all the answers

    What action should be taken when a Lewis structure has too many electrons after fulfilling the octet rule?

    <p>Form double or triple bonds with the central atom as needed</p> Signup and view all the answers

    What is the expected formal charge for a stable molecule?

    <p>As close to zero as possible for each atom</p> Signup and view all the answers

    In what scenario would an atom be assigned a formal charge greater than zero?

    <p>When it has more bonds than electrons</p> Signup and view all the answers

    What is the first step in writing a Lewis structure for a compound?

    <p>Draw the skeletal structure of the compound</p> Signup and view all the answers

    If a molecule has a positive charge, how is the formal charge calculated?

    <p>By counting one less electron for each positive charge</p> Signup and view all the answers

    Which option best describes the role of d orbitals in Lewis structure construction?

    <p>They allow for the potential of forming additional bonds</p> Signup and view all the answers

    What does the octet rule indicate about an atom's preferred electron configuration?

    <p>An atom prefers to have a full outer shell with 8 electrons.</p> Signup and view all the answers

    In the formation of NaCl, what happens to sodium's valence electron?

    <p>Sodium loses its valence electron to achieve a stable octet.</p> Signup and view all the answers

    What is the electron configuration of the Na+ ion?

    <p>1s2 2s2 2p6</p> Signup and view all the answers

    What is the approximate electron configuration of Cl- ion?

    <p>1s2 2s2 2p6 3s2 3p6</p> Signup and view all the answers

    What type of bond is formed between Na+ and Cl- ions?

    <p>Ionic bond</p> Signup and view all the answers

    Which of the following statements is true regarding covalent bonds?

    <p>Covalent bonds involve sharing electrons to achieve stability.</p> Signup and view all the answers

    Which element has an exception to the octet rule due to its electron capacity?

    <p>Hydrogen</p> Signup and view all the answers

    What happens to chlorine atoms when they form ionic compounds?

    <p>Chlorine accepts an electron to complete its octet.</p> Signup and view all the answers

    Study Notes

    Bonds and Examples

    • Carbon monoxide (CO) features a coordinate bond between carbon (C) and oxygen (O).
    • Ammonium ion (NH4) forms when ammonia (NH3) gains a proton (H+).
    • Hydronium ion (H3O) results from water (H2O) accepting a proton.

    Drawing Lewis Structures

    • Start by counting total valence electrons; add or subtract electrons based on ion charges.
    • Construct a skeletal structure connecting atoms with bonds.
    • Place the least electronegative element in the center of the structure.
    • Complete the octet for all atoms except hydrogen, which follows the duet rule.
    • If necessary, create double or triple bonds to accommodate too many electrons.

    Octet Rule

    • Atoms seek to have 8 electrons in their highest energy level to achieve stability.
    • Sodium (Na+) loses one electron to achieve a stable octet, while Chlorine (Cl-) gains one.
    • Sodium chloride (NaCl) forms when sodium donates its valence electron to chlorine.

    Types of Chemical Bonds

    • Ionic bonds occur via electrostatic attraction between positively and negatively charged ions.
    • Covalent bonds share electrons between atoms, including single, double, and triple bonds.
    • Hydrogen is a special case, only able to hold 2 electrons due to its position in the periodic table.

    Bond Lengths

    • The bond length decreases as the number of bonds increases; for example, C-C bond lengths are:
      • Single bond: 1.54 Å
      • Double bond: 1.34 Å
      • Triple bond: 1.20 Å

    Dative Bonds

    • Dative (or coordinate) bonds occur when one atom donates both electrons for bonding.
    • For dative bonds, the donor must have a lone pair of electrons, and the acceptor should have an empty orbital.

    Writing Lewis Structures Steps

    • Arrange remaining electrons to satisfy hydrogen's duet and other atoms' octets after forming initial bonds.
    • If insufficient electrons remain, employ d orbitals from Period 3 or beyond to expand octets.
    • If there are extra electrons, form multiple bonds as needed.

    Formal Charge

    • Formal charge assesses the distribution of electrons in a Lewis structure, with the ideal being closest to zero.
    • The sum of formal charges should equal zero for neutral molecules or the overall charge for polyatomic ions.
    • A stable Lewis structure has minimal formal charges and negative charges on more electronegative atoms.

    Resonance Structures

    • Molecules with multiple bonds and lone pairs can exhibit resonance.
    • Structures must have valid electron pair arrangements to describe resonance effectively.

    Exceptions to the Octet Rule

    • Incomplete octets occur when central atoms possess fewer than 8 electrons, as seen in boron trifluoride (BF3).
    • Expanded octets are observed in elements like phosphorous and sulfur.
    • Odd-electron compounds, such as nitric oxide (NO), do not adhere to the octet rule.

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    Description

    This quiz covers the fundamental concepts of chemical bonds, including coordinate, ionic, and octet rule principles. It also delves into the process of drawing Lewis structures, providing a systematic approach to determining molecular connectivity. Test your knowledge on the examples and rules governing these essential topics in chemistry.

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