VSEPR & Hybridization (College Board AP® Chemistry): Flashcards
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- FrontVSEPR Theory
Define VSEPR theory.
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Cards in this collection (15)
Define VSEPR theory.
VSEPR theory (valence shell electron pair repulsion theory) is a model that predicts molecular geometry by stating that electron groups around a central atom arrange themselves as far apart as possible to minimize Coulombic repulsion.
According to VSEPR theory, lone pairs exert .......... repulsion than bonding pairs, causing bond angles to compress.
According to VSEPR theory, lone pairs exert greater repulsion than bonding pairs, causing bond angles to compress.
Why is the H–N–H bond angle in ammonia (NH3) approximately 107° rather than 109.5°?
The lone pair on nitrogen exerts stronger Coulombic repulsion than the bonding pairs, pushing the three N–H bonds closer together and compressing the bond angle from the ideal tetrahedral value of 109.5° to approximately 107°.
True or False?
A molecule with four electron groups and two lone pairs has a tetrahedral molecular geometry.
False.
A molecule with four electron groups and two lone pairs has a bent (angular) molecular geometry, with a bond angle of approximately 104.5°. Tetrahedral geometry requires four bonding groups and no lone pairs.
CCl4 has four polar C–Cl bonds, yet the molecule is nonpolar overall. Why?
CCl4 has a tetrahedral geometry in which all four C–Cl bond dipoles are arranged symmetrically. The dipole moments point in directions that exactly cancel each other, giving a net dipole moment of zero and making the molecule nonpolar.
A molecule with five electron groups, all bonding, has a .......... molecular geometry with equatorial bond angles of 120° and axial bond angles of 90°.
A molecule with five electron groups, all bonding, has a trigonal bipyramidal molecular geometry with equatorial bond angles of 120° and axial bond angles of 90°.
True or False?
A triple bond counts as three separate electron groups in VSEPR theory.
False.
A triple bond counts as one electron group in VSEPR theory, regardless of the number of bonds, because all electrons in the triple bond occupy the same region of space between the two atoms.
How does bond order affect relative bond length and bond energy?
Higher bond order means more electron pairs are shared between atoms, increasing Coulombic attraction and resulting in a shorter bond length and higher bond energy. Triple bonds are shorter and stronger than double bonds, which are shorter and stronger than single bonds.
Define sigma bond.
Sigma bond is a covalent bond formed by the end-to-end overlap of atomic orbitals, resulting in electron density concentrated directly along the internuclear axis.
A pi bond is formed by the .......... overlap of adjacent p-orbitals, with electron density located above and below the plane of the sigma bond.
A pi bond is formed by the sideways (lateral) overlap of adjacent p-orbitals, with electron density located above and below the plane of the sigma bond.
True or False?
A sigma bond is stronger than a pi bond.
True.
Sigma bonds form by end-to-end overlap, which creates greater orbital overlap along the internuclear axis, resulting in a stronger bond with higher bond energy than a pi bond's sideways overlap.
A molecule of ethyne (C2H2) contains a triple bond between the two carbon atoms. How many sigma bonds and how many pi bonds are present in ethyne in total?
Ethyne contains 3 sigma bonds (one C–C sigma bond and two C–H sigma bonds) and 2 pi bonds (the two additional bonds in the C≡C triple bond). Every bond contains exactly one sigma bond; pi bonds account for the remainder.
In any covalent bond, there is always exactly .......... sigma bond; additional bonds in a double or triple bond are pi bonds.
In any covalent bond, there is always exactly one sigma bond; additional bonds in a double or triple bond are pi bonds.
True or False?
Pi bonds allow free rotation about the bond axis.
False.
Pi bonds restrict rotation because their electron clouds above and below the sigma bond plane would break during rotation. Free rotation occurs only around sigma bonds.
Why does a double bond have greater bond energy than a single bond between the same two atoms?
A double bond consists of one sigma bond and one pi bond. The additional pi bond provides extra Coulombic attraction between the electrons and nuclei, requiring more energy to break the bond overall compared to a single sigma bond alone.
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