Chapter 11 Chemistry

What describes the formation of sp² hybrid orbitals?

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

What describes molecular orbital bond orders?

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

What describes a π bond?

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

What describes σ and π molecular orbitals?

- A π bonding molecular orbital has two regions of high electron density. - Both atomic s and p orbitals can form σ molecular orbitals. - Atomic p orbitals can combine to form either σ or π molecular orbitals.

Valence Bond Theory Molecular Orbital Theory

- Atoms are bonded through localized overlap of half-filled, hybridized, valence-shell atomic orbitals. - A molecule is seen as a collection of nuclei with orbitals delocalized over the whole molecule.

What describes the molecular orbital description of the bonding in the O₂ molecule?

- O₂ is paramagnetic (this is only possible if O₂ has one or more unpaired electrons, which can't be reconciled with the most stable Lewis structure predicted by VB theory). - The bond order is equal to 2. - O₂ is more reactive than N₂ (Both VB and MO theory indicate that O₂ has a weaker bond than N₂, but MO theory also shows the presence of unpaired electrons in O₂, which decrease stability and increase reactivity).

What describes σ bonds?

- Single bonds are σ bond. - A σ boned results from end-to-end overlap of two orbitals.

What describes an MO energy-level diagram?

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

What also describes Hybrid orbitals?

- The spatial orientations of the hybrid orbitals match observed molecular shapes. - The shape and orientation of a hybrid orbital allows maximum overlap with an orbital from another atom to form a bond. - The type of hybrid orbital formed varies depending on the specific combination of atomic orbitals.

The molecular orbital bond order

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A double ______ σ and _______π bond(s). A double bond is _______ than a single bond.

1, 1, Stronger.

What are the steps of determining the hybridization of an atom?

1.) Draw a Lewis structure using the molecular formula. 2.) Count the number of electron groups surrounding the central atom. 3.) The number of bonding orbitals required is equal to the number of electron groups. 4.) Build the appropriate combination of atomic orbitals based on the number of bonding orbitals required.

What is the formula for calculating molecular orbital bond order?

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

σ bond π bond

Allows free rotation about the bond axis Restricts rotation about the bond axis.

σ₂p orbital π₂p orbital

Formed by end-to-end combinations of atomic 2p orbitals. Formed by side-to-side combinations of atomic 2p orbitals.

Valence bond theory describes covalent bonding as the localized overlap of half-filled valence-shell ______ atomic orbitals. Molecular orbital theory, on the other, describes a molecule as a collection of nuclei with orbitals _____ over the whole molecule.

Hybrid, Delocalized.

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

Hybridization, Hybrid,

sp sp² sp³ sp³d sp³d²

Linar Trigonal Planar Tetrahedral Trigonal Bipyramidal Octahedral

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.

In a covalent bond, the bonding MOs, will be closer in energy to the AOs of the _______ electronegative atom.

More.

Atomic orbitals that aren't involved in bonding are called _______ MOs. These MOs will have ______ energy as/to the isolated atomic orbitals.

Nonbinding, The Same.

Hybrid orbitals are designed 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 were combined to form this orbital type.

Number, 1, 2.

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

What describes hybrid orbitals?

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

Valence bond theory describes a single covalent bond as the ______ of orbitals from two atoms to form a shared space, which is occupied by ______ electron(s).

Overlap, 2.

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

Paramagnetic, Diamagnetic.

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.

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 σ₁s* 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, Nuclei

σ₂p σ₂p* and π₂p* π₂p

Single region of high electron density between bonded nuclei. Zero electron density between bonded nuclei Two separate region of high electron density between nuclei, above and below bond axis.

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

There is a large energy difference between the 2s and 2p orbitals of O, F, and Ne; therefore no s-p mixing occurs when molecular orbitals are formed.

When should the VSEPR model and hybridization theory be applied to describe bonding?

Whenever an observed molecular shape needs to be rationalized in terms of atomic orbitals.

A central atom can be surrounded by five or six electron group if _______ orbitals are available for bonding. The appropriate number of equivalent bonding orbitals is formed by combining ______ s orbital(s), _______ p orbital(s), and one or two _______ orbitals.

d, One, Three, d.

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

sp, Two

The combination of one s and two p orbitals will form a group of three _______ hybrid orbitals. These hybrid orbitals adopt a(n) ______ planar geometry, and are at an angle of _____° to the remaining unhybridized p orbitals.

sp², Trigonal, 90.

What describes the bonding and antibonding molecular orbitals?

- An antibonding molecular orbital has a region of zero electron density between the nuclei of the bonding electron density. - A bonding molecular orbital is formed by addition of the wave functions for two atomic orbitals. - A bonding molecular orbital is lower in energy than the original atomic orbitals.

Consider the combination of two atomic orbitals to form a pair of molecular orbitals, designated σ₂s and σ₂s*. What describes these designations correctly?

- Both orbitals are designated σ because they are cylindrically symmetrical. - The atomic orbitals that combine in this case are s orbitals.

What describes the rules used for placing electrons in molecular orbitals?

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

What describes the general principle of molecular orbital theory?

- The addition of two wave functions produces a region increased electron density. - Bonding involves the addition and subtraction of wave function. - Orbitals are viewed as wave functions.

Why is the hybridization model necessary to explain the bonding in a molecule such as CH₄?

- The atomic electron configuration of carbon can't account for four equivalent bonds. - The observed bond angles can't be explain with reference to atomic orbitals.

What describes sp³ orbitals?

- 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.

What describes the hybridization of s, p, and d orbitals?

- The hybridization of an atom surrounded by six electron pairs is sp³d². - Only elements from Period 3 onward can use d orbitals for bonding.

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, and the _______ of hybrid orbitals varies according to the specific orbitals mixed.

Atomic, Equal, Type.

According to valence bond theory, a(n) ______ bond is formed by the overlap of orbitals from two atoms. In order to explain the observed bond angles in many species it is proposed that the atomic orbitals first form _____ orbitals, which differ from the orbitals of the isolated atoms.

Covalent, Hybrid.

Molecular orbitals can be formed by the combination of multiple atomic orbitals, allowing electrons to be _______ or shared between several atoms. The molecular orbital model therefore allows a better description of the bonding in ______ structures than VB theory, which depicts electrons as being ______ between two atoms at a time.

Delocalized, Resonance, Localized.

Why is rotation about a π bond restricted?

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

What describes Valence Bond Theory?

The space formed by overlapping orbitals can accommodate a maximum of two electrons. - The extent of orbital overlap depends on the shape and direction of the orbitals involved. - A shared electron pair has the highest probability of being located between the nuclei of the bonded atom.

A double bond acts as ________ electron group(s) even though there is/are _____ electron pair(s) shared between the bonding atoms. This is because each electron pair occupies a different orbital, which reduces _______ between them. Similarly the three bonds of a triple bond form ____ group(s).

Two, Repulsions, One.

According to the molecular orbital model of covalent bonding, orbitals are viewed as ______ functions. The formation of a bond involves the mathematical combination of these functions, by either by ______ to give an area of increased electron density, or by ______ to give an area of decreased electron density.

Wave, Addition, Subtraction.

Place the molecular orbitals in order of decreasing energy for species of O₂, F₂, and Ne₂. Start with the highest energy orbital at the top of the list.

σ₂p* π₂p* π₂p σ₂p

Place the molecular orbitals in order of decreasing energy for species of B₂, C₂, and N₂. Start with the highest energy orbital at the top of the list.

σ₂p* π₂p* σ₂p π₂p