AP Chemistry:: Molecular Ionic Compound Structure

What is an IONIC BOND, and between what general TYPES of elements does it typically form?

- **A)** This type of bond has no actual relationship to the electrostatic attraction between oppositely charged ions
- **B)** An ionic bond refers to two atoms SHARING a pair of electrons equally, rather than one atom transferring electrons to another
- **C)** A bond formed by the ELECTROSTATIC ATTRACTION between OPPOSITELY charged ions, typically forming when a METAL (which loses electrons to form a cation) bonds with a NONMETAL (which gains electrons to form an anion)
- **D)** Ionic bonds typically form between two NONMETALS, rather than between a metal and a nonmetal

What is a COVALENT BOND, and between what general TYPES of elements does it typically form?

- **A)** A bond formed when two atoms SHARE one or more pairs of electrons, typically occurring between two NONMETAL atoms
- **B)** Covalent bonds typically form between a METAL and a NONMETAL, rather than between two nonmetals
- **C)** A covalent bond refers to the complete TRANSFER of an electron from one atom to another, rather than electron sharing
- **D)** This type of bond has no actual relationship to atoms sharing electrons with each other

What is a POLAR COVALENT BOND, and how does it differ from a NONPOLAR covalent bond?

- **A)** A polar covalent bond refers to electrons being shared PERFECTLY EQUALLY between two atoms, identical to a nonpolar bond
- **B)** This type of bond has no actual relationship to unequal electron sharing due to an electronegativity difference
- **C)** A covalent bond in which electrons are shared UNEQUALLY between two atoms (due to a difference in electronegativity), giving the bond a partial positive and partial negative end -- unlike a nonpolar covalent bond, where electrons are shared EQUALLY
- **D)** Polar covalent bonds only ever form between two atoms of the exact SAME element, which would actually always be nonpolar

How does the ELECTRONEGATIVITY DIFFERENCE between two bonded atoms generally determine whether their bond is classified as NONPOLAR COVALENT, POLAR COVALENT, or IONIC?

- **A)** A SMALL electronegativity difference (roughly 0 to 0.4) typically indicates a NONPOLAR covalent bond, a MODERATE difference (roughly 0.4 to 1.7) typically indicates a POLAR covalent bond, and a LARGE difference (greater than about 1.7) typically indicates an IONIC bond
- **B)** Bond classification depends only on which SPECIFIC elements are involved, with electronegativity difference playing no actual role
- **C)** Electronegativity difference has no actual relationship to classifying a bond as nonpolar covalent, polar covalent, or ionic
- **D)** A LARGE electronegativity difference always indicates a NONPOLAR covalent bond, while a SMALL difference indicates an ionic bond (the reverse of the actual relationship)

What is a LEWIS STRUCTURE (or Lewis dot structure), and what does it visually represent about a molecule?

- **A)** A diagram that shows how VALENCE ELECTRONS are arranged within a molecule, including BONDING pairs (shared between atoms) and LONE (non-bonding) pairs on individual atoms
- **B)** Lewis structures show only PROTONS and NEUTRONS within a molecule's nuclei, with no representation of electrons at all
- **C)** This type of diagram has no actual relationship to representing a molecule's valence electron arrangement
- **D)** A Lewis structure represents only a molecule's overall THREE-DIMENSIONAL shape, with no actual information about electron arrangement

What is the OCTET RULE, as a general guideline for predicting how many bonds/electrons a main-group atom will typically have in a stable molecule?

- **A)** Atoms following the octet rule always end up with SIXTEEN valence electrons, rather than eight
- **B)** Atoms tend to gain, lose, or SHARE electrons in order to achieve a total of EIGHT valence electrons (a full outer shell, resembling the electron configuration of a noble gas), which is generally a particularly STABLE arrangement
- **C)** This rule has no actual relationship to predicting a stable number of valence electrons for a main-group atom
- **D)** The octet rule states that atoms always prefer to have exactly ONE valence electron, rather than eight

What is a notable EXCEPTION to the octet rule, specifically regarding atoms that can have an 'EXPANDED OCTET' (more than 8 valence electrons)?

- **A)** Expanded octets only ever occur for elements in PERIOD 2 (like carbon or nitrogen), never for Period 3 or lower elements
- **B)** This exception has no actual relationship to elements in Period 3 or below accommodating additional valence electrons
- **C)** Certain elements in PERIOD 3 or below (like phosphorus or sulfur) can accommodate MORE than 8 valence electrons in some compounds, since they have access to available d-orbitals that can participate in additional bonding
- **D)** Every single element, without exception, is ALWAYS limited to exactly 8 valence electrons, with no possible expanded-octet exceptions

What is RESONANCE, in the context of Lewis structures, and why is a molecule exhibiting resonance NOT accurately described by any single Lewis structure alone?

- **A)** Resonance means a molecule can be PERFECTLY and COMPLETELY described by exactly one single Lewis structure, with no need to consider multiple structures
- **B)** This concept has no actual relationship to a molecule's electron distribution being best described by multiple contributing structures
- **C)** Resonance occurs when a molecule's actual electron distribution is best described as an AVERAGE (hybrid) of TWO OR MORE valid Lewis structures that differ only in the position of certain electrons -- no single structure alone captures the molecule's true, blended electron distribution
- **D)** Resonance structures always represent completely DIFFERENT molecules, rather than different valid depictions of the SAME molecule