CHEM 111 smart book 10

- formation of covalent bonds - breaking of covalent bonds

- exothermic process - endothermic process

A double bond is always made up of _____ σ and _____ π bond(s). A double bond is _____ than a single bond.

1, 1, stronger

Which of the following is the correct molecular orbital diagram for the anionic species C2- ? (Note that only molecular orbitals formed from valence atomic orbitals have been included.)

A

Why is rotation about a π bond restricted?

Free rotation would disrupt the parallel arrangement of the p orbitals, causing the bond to break.

True or false: Molecular orbital theory applies differently for homonuclear diatomic species and heteronuclear diatomic species.

true

The lower the molecular orbital bond order, the _____ the bond and the _____ stable the species.

weaker, less

The bonding in a resonance hybrid is often described using a combination of bonding models. Valence bond theory and hybridization are used to describe the _____ bonds, while the _____ bonds are better described using the molecular orbital model.

σ, π

A triple bond is composed of ________ σ and ________ π bond(s).

- 1 - 2

- Linear - Trigonal planar - tetrahedral - trigonal bipyramidal - octahedral

- 2 domains - 3 domains - 4 domains - 5 domains - 6 domains

Which of the following options correctly describe the rules used for placing electrons in molecular orbitals? Select all that apply.

- If two molecular orbitals have equal energy, an electron must be placed in each orbital before pairing up. - Orbitals are filled in order of increasing energy. - Lower-energy orbitals are filled before placing electrons in higher-energy orbitals.

Which of the following statements correctly describe an excited state of an atom? Select all that apply.

- In an excited state, one or more electrons occupy a higher energy orbital than the ground state. - The notation C* denotes the excited state of a C atom.

Which of the following statements correctly describe sp3 hybrid orbitals? Select all that apply.

- The four sp3 hybrid orbitals of a group are equivalent in shape and energy. - An sp3 hybrid orbital is unsymmetrical in shape, having one small and one large lobe.

Why is the hybridization model necessary to explain the bonding in a molecule such as CH4? Select all that apply.

- The observed bond angles cannot be explained with reference to unhybridized orbitals. - The atomic electron configuration of carbon cannot account for four equivalent bonds.

The Lewis structure for the resonance hybrid FNO2 is shown (formal charges are not included). Which of the following statements correctly describe the bonding in this species, using a combination of bonding models? Select all that apply.

- The π bond is delocalized between the N atom and the two O atoms. - There are three π molecular orbitals, formed from the combination of three p atomic orbitals, one each from the N and the two O atoms.

A central atom can be surrounded by 5 or 6 electron domains if _______ orbitals are available for bonding. The appropriate number of equivalent bonding orbitals is formed by combining ______ s orbital(s), ______ p orbital(s), and 1 or 2 ______ orbitals.

- d - 1 - 3 - d

- sigma bond - pi bond

- does rotate because the bonds are formed along the bond axis - does not rotate because the bonds are formed by parallel overlap

- σ2p orbital - π2p orbital

- formed by end-to-end combination of atomic 2p orbitals - formed by side-to-side combination of atomic 2p orbitals

Molecular geometry is determined by the number of electron domains around a central atom, where an electron domain may be a(n) _______ pair or any ______ between two atoms.

- lone - bond

A group of sp3 hybrid orbitals is formed by the hybridization of _______ s and ________ p orbital(s) from the valence shell of an atom. These hybrid orbitals have the same ______ and energy.

- one - three - shape

The valence molecular orbital diagram for Li2- is shown. The molecular orbital bond order for this species is equal to _____ and Li2- is _____ stable than Li2.

1/2, less

Why are the terms "axial" and "equatorial" not used to describe the bonds in an octahedral system?

All six bonds are equivalent in an octahedral system.

Select the partial orbital diagram that correctly shows the hybrid orbitals and electron distribution of the O atom in the molecule OF2.

B

Which statement correctly describes the basic principle of the VSEPR model?

Each electron domain around a central atom is located as far from the others as possible.

The correct notation for an excited-state oxygen atom is ______.

O*

Which of the following cannot be accounted for using the valence bond model of bonding?

The magnetic properties of molecules

The electron-domain geometry of a species is the arrangement of _____ around the central atom, whereas the molecular geometry is the arrangement of _____.

electron domains, bonded atoms

The formation of covalent bonds is ______ because energy is ______.

exothermic; released when the bonds are created

In general, the smaller the bond angle the _____ the electron repulsions for the groups concerned. In a five electron-domain system lone pairs prefer to occupy _____ positions because equatorial-equatorial repulsions are _____ than axial-equatorial repulsions.

stronger, equatorial, weaker

The _______ shell is the outermost electron-occupied shell in an atom. (Use the specific term used to describe the outer shell.)

valence

The structure shown contains _______ σ bond(s) and ______ π bond(s).

- 6 - 2

Which of the following statements correctly describe bonding and antibonding molecular orbitals? Select all that apply.

- A bonding molecular orbital is formed by constructive combination of two atomic orbitals. - An antibonding molecular orbital has two lobes and does not lie between the bonding nuclei. - A bonding molecular orbital is lower in energy than the original atomic orbitals.

- Nonpolar molecule - Polar molecules

- A molecule having no dipole moment - A molecule having a dipole moment

- Electron-domain geometry - Molecular geometry

- Arrangement of bonds and lone pairs around the central atom - Arrangement of bonded atoms around the central atom

The valence molecular orbital diagram for Be2+ is shown. Which of the following statements correctly interpret this diagram? Select all that apply.

- Be2+ is more likely to exist than Be2. - Be2+ has a weaker bond than H2. - The molecular orbital bond order for Be2+ is 1/2

Which of the following statements correctly describe the bonding in benzene? Select all that apply.

- Benzene has six electrons in bonding π molecular orbitals. - Three bonding π molecular orbitals are formed when six p orbitals combine in benzene.

Which of the following molecules has at least one bond angle of 120°? Select all that apply.

- CH2O - PCl5

Which of the following options correctly describe sp hybrid orbitals? Select all that apply.

- Each sp hybrid orbital has one large and one small lobe. - The energy of an sp hybrid orbital lies between the energies of the original s and p orbital that were mixed.

The valence molecular orbital diagram for the cation F2+ is shown. Which of the following options correctly interpret this diagram? Select all that apply.

- F2+ has a stronger bond than F2. - The molecular orbital bond order is equal to 3/2.

Which of the following statements correctly describe how to determine whether a given molecule is polar or nonpolar? Select all that apply.

- For a molecule that has polar bonds, the geometry must be known in order to predict the overall polarity. - If a molecule contains no dipole moments across any bonds, it will be nonpolar. - If the individual bond dipoles do not cancel, the molecule is polar.

Which of the following statements correctly describe how to determine the electron-domain geometry of a species using the VSEPR model? Select all that apply.

- If lone pairs are present, the molecular geometry will differ from the electron-domain geometry. - The total number of electron domains around the central atom gives the electron-domain geometry. - Use the molecular formula to draw the Lewis structure.

Which of the following are correct regarding molecular orbitals in heteronuclear diatomic species?

- The atomic orbitals of the more electronegative atom are lower in energy. - The lower-energy atomic orbital contributes more to the bonding molecular orbital. - The higher-energy atomic orbital contributes more to the antibonding molecular orbital.

The Lewis structure for the molecule NF3 is shown. Which of the following statements correctly describe the bonding in this molecule? Select all that apply.

- The bond angles for this molecule are slightly less than 109.5o. - The N uses one sp3 hybrid orbital to form each N-F bond.

Select the correct statements regarding the strength of a double bond.

- The double bond is stronger than the single bond, but not by twice the energy. - The sideways overlap of p orbitals is not as effective as the overlap of hybrid orbitals that point directly towards one another.

Which of the following statements correctly describe the formation of sp2 hybrid orbitals? Select all that apply.

- The formation of sp2 hybrid orbitals leaves one unhybridized valence p orbital. - A group of sp2 hybrid orbitals assumes a trigonal planar geometry.

Which of the following statements correctly describe molecular orbital bond orders? Select all that apply.

- The lower the molecular orbital bond order, the weaker the bonds between the atoms of the species. - A species with more electrons in bonding than antibonding molecular orbitals will have a positive molecular orbital bond order.

The valence molecular orbital diagram for the anion B2- is given. Which of the following options correctly interpret this diagram? Select all that apply.

- The molecular orbital bond order is equal to 3/2. - B2- is paramagnetic. - B2- has a shorter bond than B2.

Which of the following options correctly describe a molecular orbital energy level diagram? Select all that apply.

- The molecular orbital diagram typically includes valence-shell molecular orbitals only. - The molecular orbital diagram can be used to calculate bond order and predict the stability of a species. - The molecular orbital diagram shows the relative energy and number of electrons in each molecular orbital.

Which of the following statements correctly describe valence bond theory? Select all that apply.

- The overlap of orbitals to form a bond results in a lower potential energy for the system. - A covalent bond results from the attraction between nuclei of the two bonded atoms and the shared electron pair.

Which of the following statements correctly describe hybrid orbitals? Select all that apply.

- The spatial orientations of the hybrid orbitals match observed molecular geometries. - The type of hybrid orbital formed varies depending on the specific combination of atomic orbitals.

Which of the following options correctly describe the bond angles associated with each electron-domain geometry? Select all that apply.

- The trigonal bipyramidal system has two different bond angles. - A bond angle of 180° is observed for a linear system. - A species with 3 electron domains will exhibit an ideal bond angle of 120°.

Which of the following options correctly describe the C=N double bond in the structure shown? Select all that apply.

- The σ bond is formed by the end-to-end overlap of an sp2 orbital from each atom. - The π bond of the C=N bond is formed by sideways overlap of a p orbital from each atom.

- A - B - C - D - E

- Trigonal bipyramidal - Tetrahedral - Trigonal planar - Linear - Octahedral

Which of the following correctly describe the valence shell electrons of an atom? Select all that apply.

- Valence electrons are the electrons in the outermost occupied shell. - The electrons involved in bonding are always valence electrons.

- σ bond - π bond

- allows free rotation about the bond axis - restricts rotation about the bond axis

Hybrid orbitals are formed by the combination or "mixing" of ______ orbitals from a specific atom. The number of hybrid orbitals formed is ______ to/than the number of orbitals mixed.

- atomic - equal

Valence bond theory assumes that electrons in a molecule occupy ______ orbitals of the individual atoms. Conversely, molecular orbital theory describes bonding in terms of the interaction of atomic orbitals to form _______ orbitals that are associated with the entire covalent species.

- atomic - molecular

Which of the lettered options correspond to equatorial positions in the image shown? Select all that apply.

- b - c - d

According to the VSEPR model, each electron _______ around a central atom will be located as far away from the others as possible, in order to minimize electron-electron ________.

- domain - repulsions

Valence bond theory proposes that before a covalent bond forms, atomic orbitals from a given atom can combine to form new atomic orbitals. This process is called ________ of orbitals, and the new atomic orbitals are referred to as _______ orbitals.

- hybridization - hybrid

- sp - sp2 - sp3 - sp3d - sp3d2

- linear - trigonal planar - tetrahedral - trigonal bipyramidal - octahedral

Hybrid orbitals are designated by using a superscript to indicate the _____ of each type of orbital used to form them. For example, the designation sp2 indicates that ______ s and ______ p orbital(s) were combined to form this orbital type.

- number - 1 - 2

- 90° - 120° - 109.5° - 180° - 90° and 120°

- octahedral - trigonal planar - tetrahedral - linear - trigonal bipyramidal

Consider the molecule CCl4. Each C-Cl bond in this molecule is _______ because Cl and C have different electronegativities. Since CCl4 has a tetrahedral electron-domain geometry and is symmetrical, the individual bond dipoles _______ and the molecule is _______ overall.

- polar - cancel - nonpolar

Molecular orbitals formed from the combination of atomic s orbitals are called ______ molecular orbitals because they are cylindrically symmetrical. The molecular orbitals formed from atomic 1s orbitals are designated σ∗1sσ1s* for the _____ molecular orbital and σ1s for the _______ molecular orbital.

- sigma - antibonding - bonding

A bond formed by the overlap of two s orbitals or the end-to-end overlap of two orbitals that have p character is called a(n) ______ bond. This bond has its highest electron density between the ______ of the two bonded atoms.

- sigma - centers

The hybridization of one s and one p orbital will result in the formation of two _______ hybrid orbitals. This will leave _______ unhybridized valence p orbital(s), lying at right angles to the hybrid orbitals.

- sp - 2

The combination of one s and two p orbitals will form a group of three ______ hybrid orbitals. These hybrid orbitals adopt a(n) ______ hybrid orbitals. These hybrid orbitals adopt a(n) ______ o to the remaining unhybridized p orbital.

- sp2 - trigonal - 90

- If individual bond dipoles cancel - If individual bond dipoles do not cancel

- the species will be nonpolar overall. - the species will be polar overall.

Which of the following is the correct equation for calculating molecular orbital bond order? MO is an abbreviation for molecular orbital.

1/2[(electrons in bonding MOs) - (electrons in antibonding MOs)]

A double bond is stronger than a single bond, but not twice as strong. Select the statement that correctly explains this observation.

A π bond is not as strong as a σ bond because sideways overlap of orbitals is less effective than head-to-head overlap.

Which of the following statements correctly defines hybrid orbitals?

Orbitals used for bonding that are formed by mixing atomic orbitals from the same atom

Which of the following correctly describes the bond angle in a molecule of the general type ABx?

The angle between two adjacent A-B bonds

A particular hybrid orbital is designated sp3d2. What information is provided by the superscripts in this designation?

The number of each type of atomic orbital combined to produce this type of hybrid orbital

Which statement regarding hybridized orbitals and molecular geometry is correct?

The number of electron domains on the central atom dictates the number of hybrid orbitals necessary to account for the molecular geometry.

Why do the energies of the molecular orbitals formed for species of O2, F2, and Ne2 differ from those of the MOs for other period 2 elements?

There is a large energy difference between the 2s and 2p orbitals of O, F, and Ne; resulting in no s-p molecular orbital interactions.

True or false: Valence bond theory does not enable us to describe the magnetic properties of molecules.

True

Which of the following statements is correct regarding the molecular geometry of molecules with more than one central atom?

You must treat the molecule as though it has multiple central atoms.

The molecular orbital bond order is calculated as 1212[x - y] where x is the number of electrons in _____ molecular orbitals and y is the number of electrons in _____ molecular orbitals. In general, the higher the molecular orbital bond order, the _____ the bond strength for the species.

bonding, antibonding, greater

According to valence bond theory, a(n) _____ bond is formed by the overlap of orbitals from two atoms. Energy is released during the process so that the system is at a _____ potential energy after bonding.

covalent, lower

The π bonds in a molecule such as benzene are _______, or spread out over the entire molecule.

delocalized

Delocalized electrons are best described as _____.

electrons that are spread out over a number of atoms

A 5-electron group system (shown) has two different types of positions for substituents. The three positions marked "1" form a trigonal plane about the central atom and are called _____ positions while the two positions marked "2" are _____ positions.

equatorial, axial

What approximate value will be observed for the bond angle marked in the structure shown? (Note that Lewis structures commonly do not reflect the actual shape of the species.)

less than 109.5

A molecular orbital is a region of space in a covalent species where electrons are likely to be found. The combination of two atomic orbitals always forms two molecular orbitals; the bonding molecular orbital, which is _____ in energy, and the antibonding molecular orbital, which is _____ in energy, than the original atomic orbitals.

lower; higher

Molecular orbital theory views bonding as the combination of atomic orbitals to form ______ orbitals, which belong to the species as a whole.

molecular

In general, a lone pair repels bonding electron pairs _____ than bonding pairs repel each other. A lone pair will therefore _____ the bond angle between bonding pairs.

more, decrease

All six positions in the ______ geometry system are considered equivalent.

octahedral

A molecular species with one or more unpaired electrons in a molecular orbital is ______ and will be attracted to a magnetic field, whereas a species with no unpaired electrons in its molecular orbitals is ______ and will be slightly repelled by a magnetic field.

paramagnetic, diamagnetic

The end-to-end combination of a pair of atomic p orbitals gives a pair of _____ molecular orbitals, whereas side-to-side combination produces a pair of _____ molecular orbitals. A group of three atomic p orbitals will always give rise to _____ pair(s) of π MOs and _____ pair(s) of σ molecular orbitals.

sigma, pi, 2, 1

In the structure shown, the C atom is _____-hybridized while the O atom marked 2 is _____ hybridized.

sp2, sp3

The boron atom in the structure shown requires 3 equivalent bonding orbitals, which are formed by combining _______ s and ______ p orbital(s) from the boron atom to form 3 equivalent ______ hybrid orbitals. There is(are) ________ unhybridized p orbital(s) on the boron atom, which contain(s) no electrons.

- 1 - 2 - sp2 - 1

- bent - T-shaped - square pyramidal - tetrahedral - linear

- 3 electron domains; 1 lone pair - 5 electron domains; 2 lone pairs - 6 electron domains; 1 lone pair - 4 electron domains; 0 lone pairs - 2 electron domains; 0 lone pairs

- linear - seesaw - square planar - bent - trigonal pyramidal

- 5 electron domains; 3 lone pairs - 5 electron domains; 1 lone pair - 6 electron domains; 2 lone pairs - 4 electron domains; 2 lone pairs - 4 electron domains; 1 lone pair

Which of the following statements correctly describe the five electron-domain geometries? Select all that apply.

- A system with three electron domains will have a trigonal planar electron-domain arrangement. - An octahedral geometry indicates that there are six electron domains.

Which of the following statements correctly describe a σ bond? Select all that apply.

- All single bonds are σ bonds. - A σ bond results from end-to-end overlap of two orbitals.

- valence bond theory - molecular orbital theory

- Atoms are bonded through localized overlap of half-filled, hybridized, valence-shell atomic orbitals. - Atomic orbitals combine to form orbitals that are the property of the entire molecule.

Due to smaller nuclear charges of some Period 2 elements, which of the following are true?

- There is a change in the relative energies of the σ2px and π2py,z molecular orbitals. - Some s-p interaction takes place.

Organize the steps for determining electron-domain and/or molecular geometry in the correct order, starting with the first step at the top of the list.

- Use the... - Count the... - Determine the electron... - Determine the molecular...

In an ABx molecule, the angle between two adjacent A-B bonds is called the _______ angle. This angle is determined by the number of _______ domains surrounding the central atom.

- bond - electron

- A - B - C - D

- sp3d2 - sp3 - sp - sp2

True or false: When applying the VSEPR model to determine molecular geometry, a triple bond counts as a single electron domain even though it consists of 3 shared electron pairs.

True

True or false: Any molecule in which all of the bonds are identical will be nonpolar.

false

Lone pairs are associated with _____ atom(s), giving them _____ spatial distribution than bonding electrons. For this reason, lone pairs experience greater repulsion from neighboring lone pairs and bonding pairs.

one, more

A _____ bond restricts rotation about the bond axis while a _____ bond allows almost free rotation.

pi, sigma

A bond formed by sideways overlap of two p orbitals (one from each bonding atom) is called a(n) _____ bond. This type of bond has _____ regions of electron density.

pi; 2

Which of the following statements correctly describe the general principles of molecular orbital theory? Select all that apply.

- Bonding involves the formation of new orbitals that belong to the molecule as a whole. - Atomic orbitals combine to form an equal number of molecular orbitals.

Consider the combination of two atomic orbitals to form a pair of molecular orbitals, designated σ2s and σ2s*σ2s*. Which of the following statements explain these designations correctly? Select all that apply.

- Both orbitals are designated σ because they lie along the internuclear axis. - The atomic orbitals that combine in this case are s orbitals.

Which of the following options correctly describe the structure shown? Select all that apply.

- C1 will have a tetrahedral geometry. - The bond angles around C2 are approximately equal to 180°. - C2 will have a linear geometry.

Which species has a net dipole moment (i.e., are polar overall)? Select all that apply.

- CH2Cl2 - NBr3

Which of the following statements correctly describe the arrangement of lone pairs in systems with 5 and 6 electron domains? Select all that apply.

- In a trigonal bipyramidal system lone pairs prefer to occupy equatorial positions. - If there are two lone pairs in an octahedral system they will be located opposite each other.

Which of the following statements about the orientation of lone pairs on the central atom of a trigonal bipyramidal electron system are correct?

- Lone pairs are placed to minimize the number of strong repulsive attractions. - Lone pairs occupy equatorial positions because that puts them at 90∘ to only two other domains.

Which of the following statements apply to nonpolar molecules? Select all that apply.

- Nonpolar molecules are typically symmetrical. - Nonpolar molecules do not have a net dipole moment. - Nonpolar molecules can have polar or nonpolar bonds.

- Paramagnetic - Diamagnetic

- One or more unpaired electrons present - No unpaired electrons present

Which of the following statements correctly describe the different models of bonding? Select all that apply.

- The VSEPR model can predict but not explain observed molecular geometries. - Molecular orbital theory describes bonding as the constructive and destructive combination of atomic orbitals. - A Lewis structure can be used to predict the molecular geometry of many covalent species.

Which of the following options correctly describe the hybridization of s, p, and d orbitals? Select all that apply.

- The hybridization of an atom surrounded by 6 electron domains is sp3d2. - Only elements from period 3 onward can use d orbitals for bonding.

- sp - sp3d - sp2 - sp3 -sp3d2

- two p - four d - one p - none - three d

The structure shown contains _____ σ bonds and _____ π bonds.

6; 1

Which of the following is the correct molecular orbital diagram for the cationic species Be2+? (Note that only molecular orbitals formed from valence atomic orbitals have been included.)

B

Why is BeF2 a nonpolar molecule?

BeF2 is linear and therefore the individual bond dipoles cancel to give no net dipole.

Select the partial orbital diagram that correctly shows the hybrid orbitals and electron distribution of the N atom in the molecule NBr3.

C

- Valence bond theory - Hybridization - Molecular orbital theory

- A covalent bond is formed by the overlap of atomic orbitals from each of the bonding atoms. - Atomic orbitals "mix" or hybridize to form hybrid orbitals, which can then overlap to form bonds. - Atomic orbitals combine both constructively and destructively to form bonding and antibonding orbitals.

Why do some bond angles deviate from ideal bond angles?

- A lone pair on a central atom is attracted only to the nucleus of that atom, causing it to occupy more space. - A lone pair takes up more space than a bonding pair of electrons. - Multiple bonds contain more electron density and therefore repel more strongly than single bonds.

- A - X - B

- Central atom in structure - Number of bonding electron groups - Surrounding atom

Electrons that are spread out over three or more atoms are described as being ______, whereas electrons confined between two specific atoms are described as ______.

- delocalized - localized

The triple bond in the structure shown consists of a σ bond formed by the overlap of a(n) _____ orbital on the C with a(n) _____ orbital on the N to form the σ bond. The π bonds are formed by the overlap of two pairs of _____ orbitals.

sp, sp, p

To classify geometry, a structure is assigned a specific ABx designation, where A is the ________ atom, B is a different element that is bonded to A, and x is an integer from 2 to _______.

- central - 6

Which of the following statements correctly describe a π bond? Select all that apply.

- A multiple bond always contains at least one π bond. - A π bond is formed by the side-to-side overlap of two p orbitals.

Which of the following steps are necessary to determine the hybridization of the central atom? Select all that apply.

- Count the number of electron domains on the central atom. - Draw the Lewis structure of the molecule. - Deduce the hybridization of the central atom based on the number of electron domains on the central atom.

Arrange the steps for hybridizing the orbitals of an atom in the correct order, with the first step at the top of the list.

- Draw a... - The number... - Combine the... - Place electrons..