Molecular Geometry and Bonding theories

Question 1

The * theory is a theory used to predict probable shapes of molecules and polyatomic ions based on the mutual * of electron pairs found in the valence shell of the central atom in the structure.

Electron pairs repel each other, whether they are in chemical bonds (bond pairs) or unshared (lone pairs). Electron pairs assume orientations about an atom to *

Answer 1

valence-shell electron-pair repulsion (VSEPR)
repulsions

minimize repulsions.

Question 2

• refers to the geometrical distribution about a central atom of the electron pairs in its valence shell.

Answer 2

Electron-group geometry

Question 3

• refers to the geometric shape of a molecule or polyatomic ion. In a species in which all electron pairs are bond pairs, the molecular geometry is the
• as the electron-group geometry.

Answer 3

Molecular geometry,

same

Question 4

Lone-pair electrons spread out more than do bond-pair electrons. Thus the amount of repulsion between bonding pairs (BP) and lone pairs (LP) is related by:

Answer 4

LP-LP > LP-BP > BP-BP

Question 5

• is a measure of the extent to which a separation exists between the centers of positive and negative charge within a molecule.

Answer 5

Dipole moment μ

Question 6

However, lewis theory and VSEPR method do not yield quantitative information about *. Also, Lewis theory has problems with odd-electron species and resonance structures.

Answer 6

bond energies and bond lengths

Question 7

The * treats a covalent bond in terms of the * of pure or hybridized atomic orbitals. * (or electron charge density) is concentrated in the region of overlap.

Answer 7

valence bond method
overlap
Electron probability

Question 8

The valence bond method treats a covalent bond in terms of the overlap of *. Electron probability (or electron charge density) is concentrated in the region of *.

Answer 8

pure or hybridized atomic orbitals

overlap

Question 9

“Overlap” is actually an * of two orbitals.

Answer 9

interpenetration

Question 10

The valence-bond method gives a * electron model of bonding: Core electrons and lone-pair valence electrons retain the * orbital locations as
in the separated atoms, and the * of the bonding electrons is concentrated in the region of orbital overlap.

Answer 10

localized, same

charge density

Question 11

Central Themes of VB Theory
From the main principle of VB theory are derived three central ideas:
1. The region of space formed by the * orbitals has a maximum capacity of two electrons that must have opposing spins.
2. The bond strength depends on the * of the * for the shared electrons. The greater the orbital overlap, the * the bond.
3. The valence atomic orbitals in the molecule are * from those in the isolated atoms. Mathematical mixing of specific combinations of nonequivalent orbitals gives rise to * atomic orbitals that would lead to the most * bonds. This is called * .

Answer 11

overlapping
attraction, nuclei, stronger
different, new, stable
hybridization

Question 12

• refers to combining pure atomic orbitals to generate hybrid orbitals in the valence bond approach to covalent bonding.

Answer 12

Hybridization

Question 13

A hybrid orbital is one of a set of identical orbitals reformulated from pure atomic orbitals and used to describe certain * bonds.

Hybridization occurs only when bonds are being * .

Answer 13

covalent

formed

Question 14

• In a hybridization scheme, the number of hybrid orbitals equals the *

Answer 14

total number of atomic orbitals that are combined.

Question 15

trigonal-bipyramidal
linear
tetrahedral
trigonal planar
octahedral

Answer 15

sp3d
sp
sp3
sp2
sp3d2

Question 16

A sigma bond (s) results from the * overlap of simple or hybridized atomic orbitals along the * joining the nuclei of the bonded atoms.

Answer 16

end-to-end or head-to-head

straight line

Question 17

A pi bond (p bond) results from the * overlap of p orbitals, producing a high electron charge density * joining the bonded atoms.

Answer 17

side-to-side

above and below the line

Question 18

Lewis structures, VSEPR theory, and the valence-bond method make a potent combination for describing covalent bonding and molecular structures.
• However, none of these methods provides an explanation of the * of molecules, why an atom is *, or why H + 2 is a stable species.

Answer 18

electronic spectra, paramagnetic or diamagnetic

Question 19

• describes the covalent bonds in a molecule by replacing atomic orbitals of the component atoms by * belonging to the
  molecule as a whole.

Answer 19

Molecular orbital theory, molecular orbitals

Question 20

Molecular orbital theory describes the * bonds in a molecule by replacing * of the component atoms by molecular orbitals belonging to the * as a whole.

Answer 20

covalent, atomic orbitals, molecule

Question 21

Like atomic orbitals, molecular orbitals are * , but we can relate them to the probability of finding electrons in certain regions of a molecule.
• Like an atomic orbital, a molecular orbital can accommodate just two electrons,
and the electrons must have opposing spins.

Answer 21

mathematical functions

Question 22

Wave functions can combine via * (addition) which leads
to a bonding orbital or combine via * (subtraction) which
leads to an antibonding orbital.

Answer 22

constructive interference

destructive interference

Question 23

A bonding molecular orbital describes regions of * or charge density in the * between two bonded atoms.

An antibonding molecular orbital describes regions in a molecule in which there is a * or charge density between two bonded atoms

Answer 23

high electron probability, internuclear region

low electron probability

Question 24

A * describes regions of high electron probability or
charge density in the internuclear region between two bonded atoms.

An * describes regions in a molecule in which
there is a low electron probability or charge density between two bonded atoms

Answer 24

bonding molecular orbital

antibonding molecular orbital

Question 25

1. The number of molecular orbitals (MOs) formed is equal to the number of *.
2. Of the two MOs formed when two atomic orbitals are combined, one is a bonding MO at a * energy than the original atomic orbitals. The other is an antibonding MO at a * energy.
3. In * configurations, electrons enter the * energy MOs available and they enter MOs of identical energies * before they pair up.
4. The maximum number of electrons in a given MO is two.

Answer 25

atomic orbitals combined
lower, higher
ground-state, lowest, singly

Question 26

• is one-half the difference between the numbers of electrons in bonding
  and in antibonding molecular orbitals in a covalent bond.

Answer 26

Bond order

Question 27

B2, C2, N2: Due to the small energy difference between the 2s and the 2p orbitals, there is a strong 2s-2p interaction. The modified sigma2s (with some s2p
mixed in) goes down in energy, and the modified sigma2p (with some s2s mixed in) goes up in energy producing a different ordering of energy levels.

Answer 27

_ sigma
_ _ pi

_ sigma
_ _ pi

Question 28

O2, F2, Ne2: The situation is as expected due to the large energy difference
between the 2s and the 2p orbitals which leads to a weak 2s-2p interaction.

Answer 28

_ sigma
_ _ pi

_ _ pi
_ sigma

Question 29

If the atoms in the heteronuclear diatomic molecules do not differ too greatly in *, their MOs resemble those in homonuclear diatomics.

The energy of the AOs of the more electronegative atom is * than those of
the less electronegative atom.

An MO in a heteronuclear diatomic molecule has a greater contribution from the AO to which it is * in energy.

Answer 29

electronegativities

lower

closer

Question 30

Valence Bond theory considers bonds as * between one pair of atoms while Molecular orbital theory considers electrons * throughout the entire molecule

Answer 30

localized, delocalized

Question 31

A * occurs where electron density equals zero.

Answer 31

nodal plane

Question 32

extending MO theory to

condensed phases

Answer 32

Band theory