Molecular Shapes: The AXE Method, Part 2 (10.1.6)

Question 1

• Every molecule has an AXE designation that provides information about the number of atoms and lone pairs of electrons surrounding the central atom.

Answer 1

• Every molecule has an AXE designation that provides information about the number of atoms and lone pairs of electrons surrounding the central atom.

Question 2

• The AXE designation can be used to determine the geometry and bond angle(s) of a molecule.

Answer 2

• The AXE designation can be used to determine the geometry and bond angle(s) of a molecule.

Question 3

• When multiple molecular structures are possible, the structure with the lowest energy is the correct structure.

Answer 3

• When multiple molecular structures are possible, the structure with the lowest energy is the correct structure.

Question 4

The AXE designation is a method for organizing the
geometries of molecules. By determining the AXE
designation of a molecule, the geometry and bond angles can also be determined.

Answer 4

The AXE designation is a method for organizing the
geometries of molecules. By determining the AXE
designation of a molecule, the geometry and bond angles can also be determined.

Question 5

Molecules having a central atom surrounded by six atoms and no lone pairs of electrons have an AX6 designations. Molecules having an AX6 designation have an octahedral geometry and bond angles of 90º. An example of a molecule having an AX6 designation is sulfur hexafluoride. Molecules having a central atom surrounded by five atoms and one lone pair of electrons have an AX5E designations. Molecules having an AX5E designation have an square pyramidal geometry and bond angles of 90º. An example of a molecule having an AX5E designation is bromine
pentafluoride.

Answer 5

Molecules having a central atom surrounded by six atoms and no lone pairs of electrons have an AX6 designations. Molecules having an AX6 designation have an octahedral geometry and bond angles of 90º. An example of a molecule having an AX6 designation is sulfur hexafluoride. Molecules having a central atom surrounded by five atoms and one lone pair of electrons have an AX5E designations. Molecules having an AX5E designation have an square pyramidal geometry and bond angles of 90º. An example of a molecule having an AX5E designation is bromine
pentafluoride.

Question 6

Molecules having a central atom surrounded by four atoms
and two lone pairs of electrons have an AX4E2 designation.
Because there are two possible structures for this AXE
designation, the rules for determining the lowest energy
structure must be applied. Once the structure having a lone
pair-lone pair interaction has been eliminated, the structure
having the trans oriented lone pairs is the only option for
AX4E2 molecules. Molecules having an AX4E2 designation
have an square planar geometry and bond angles of 90º. An
example of a molecule having an AX4E2 designation is xenon
tetrafluoride.

Answer 6

Molecules having a central atom surrounded by four atoms
and two lone pairs of electrons have an AX4E2 designation.
Because there are two possible structures for this AXE
designation, the rules for determining the lowest energy
structure must be applied. Once the structure having a lone
pair-lone pair interaction has been eliminated, the structure
having the trans oriented lone pairs is the only option for
AX4E2 molecules. Molecules having an AX4E2 designation
have an square planar geometry and bond angles of 90º. An
example of a molecule having an AX4E2 designation is xenon
tetrafluoride.

Question 7

Molecules having a central atom surrounded by five atoms
and no lone pairs of electrons have an AX5 designations.
Molecules having an AX5 designation have an trigonal
bipyramidal geometry and bond angles of 90º and 120º. An
example of a molecule having an AX5 designation is
phosphorus pentachloride.

Answer 7

Molecules having a central atom surrounded by five atoms
and no lone pairs of electrons have an AX5 designations.
Molecules having an AX5 designation have an trigonal
bipyramidal geometry and bond angles of 90º and 120º. An
example of a molecule having an AX5 designation is
phosphorus pentachloride.

Question 8

Molecules having a central atom surrounded by four atoms
and one lone pair of electrons have an AX4E designation.
Because there are two possible structures for this AXE
designation, the rules for determining the lowest energy
structure must be applied. The structural choice with the
fewest lone pair-bonding interactions at 90º means that
molecules having an AX4E designation have an see-saw
geometry. These molecules have bond angles of 90º and
120º. An example of a molecule having an AX4E designation
is sulfur tetrafluoride.

Answer 8

Molecules having a central atom surrounded by four atoms
and one lone pair of electrons have an AX4E designation.
Because there are two possible structures for this AXE
designation, the rules for determining the lowest energy
structure must be applied. The structural choice with the
fewest lone pair-bonding interactions at 90º means that
molecules having an AX4E designation have an see-saw
geometry. These molecules have bond angles of 90º and
120º. An example of a molecule having an AX4E designation
is sulfur tetrafluoride.

Question 9

Molecules having a central atom surrounded by three atoms
and two lone pairs of electrons have an AX3E2 designation.
Because there are three possible structures for this AXE
designation, the rules for determining the lowest energy
structure must be applied. One structure can be eliminated
because of a lone pair-lone pair interaction at 90º. The
structural choice with the fewest lone pair-bonding
interactions at 90º means that molecules having an AX3E2
designation have an T-shaped geometry and bond angles of
90º. An example of a molecule having an AX3E2 designation
is chlorine trifluoride.

Answer 9

Molecules having a central atom surrounded by three atoms
and two lone pairs of electrons have an AX3E2 designation.
Because there are three possible structures for this AXE
designation, the rules for determining the lowest energy
structure must be applied. One structure can be eliminated
because of a lone pair-lone pair interaction at 90º. The
structural choice with the fewest lone pair-bonding
interactions at 90º means that molecules having an AX3E2
designation have an T-shaped geometry and bond angles of
90º. An example of a molecule having an AX3E2 designation
is chlorine trifluoride.

Question 10

Molecules having a central atom surrounded by three atoms
and two lone pairs of electrons have an AX2E3 designation.
Because there are three possible structures for this AXE
designation, the rules for determining the lowest energy
structure must be applied. After eliminating all of the
structures that have lone pair-lone pair interactions at 90º.
there is only one remaining strutural possibility. Molecules
having an AX2E3 designation have an linear geometry and
bond angles of 180º. An example of a molecule having an
AX2E3 designation is the triiodide ion.

Answer 10

Molecules having a central atom surrounded by three atoms
and two lone pairs of electrons have an AX2E3 designation.
Because there are three possible structures for this AXE
designation, the rules for determining the lowest energy
structure must be applied. After eliminating all of the
structures that have lone pair-lone pair interactions at 90º.
there is only one remaining strutural possibility. Molecules
having an AX2E3 designation have an linear geometry and
bond angles of 180º. An example of a molecule having an
AX2E3 designation is the triiodide ion.

Question 11

What is the correct AXE designation of IF5?

Answer 11

AX5E (B)

The Lewis dot structure for the iodine pentafluoride molecule is:

The central iodine is bonded to five fluorine atoms and has one lone pair of electrons associated with it. The AXE designation is AX5E, and the shape of the molecule is square pyramidal.

Question 12

Which pair of compounds both have an AX5E designation?

Answer 12

bromine pentafluoride and iodine pentafluoride (C)

Both bromine pentafluoride and iodine pentafluoride are molecules with an AXR designated geometry of AX5E

Question 13

What is the correct AXE designation for the XeO3 molecule?

Answer 13

AX3E (B)

Question 14

Sufur hexafluoride has the same AXE designation as which of the following compounds?

Answer 14

None of the above (E)

Sulfur hexafluoride, SF6, has an AX6 designated geometry. None of the choices have an AX6 designated geometry.

Question 15

What pair of compounds listed both have an AX2E3 designated geometry?

Answer 15

Xenon difluoride and triiodide ion (B)

Both xenon difluoride and triiodide ion have an AX2E3 designated geometry and a liner geometry.

Question 16

Which of the following compounds is incorrectly matched with its AXE designation?

Answer 16

All of these are correctly matched (E)

All of these compounds is correctly matches with their AXE designated geometries

Question 17

Which of the following compounds has an AX3E2 designated geometry?

Answer 17

Chlorine trifluoride (B)

Question 18

What is the bond angle associated with an AX2E3 designation?

Answer 18

180º (A)

Molecules with an AX2E3 designation have a linear geometry and a bond angle of 180º.

Question 19

Which of the following compounds has a square planar geometry?

Answer 19

xenon tetrafluoride (C)

Question 20

Which of the following pairs of AXE designations have different shapes?

Answer 20

AX4 and AX4E (C)

AX4 molecules have a tetrahedral geometry. AX4E molecules have a see-saw geometry.

Question 21

Which of the following molecules have a T-shaped geometry?

Answer 21

Iodine trichloride (A)

Iodine trichloride, ICl3, has an AXE designation of AX3E2 and has a T-shaped geometry.

Question 22

Which of the following pairs of compounds have the same AXE designation?

Answer 22

triiodide ion and xenon difluoride (C)

Both of these compounds have an AX2E3 designation and an linear geometry.

Question 23

Which of the following geometries is associated with an AX4E designation?

Answer 23

see-saw (D)

The see-saw geometry is associated with the AX4E designation.

Two of the bonded atoms are located in the axial position and the other two bonded atoms are located in the axial position with regard to the central atom. The lone pair associated with the central atom is located in an axial position.

Question 24

What is the correct AXE designation and geometry of the orthotellurate ion, TeO66−?

Answer 24

AX6, octahedral (C)

Surrounded by six bonding oxygen atoms and having no lone pairs of electrons gives the the orthotellurate ion an AX6 designated geometry. The shape of the orthotellurate ion is an octahedron.

Question 25

What is the AXE designation for the triiodide ion?

Answer 25

AX2E3 (D)

The triiodide molecule has two surrounding atoms and three lone pairs of electrons associated with the central atom; it has an AXE designated geometry of AX2E3.

Question 26

Which compound has an AX4E designation?

Answer 26

SF4 (B)

The central sulfur atom surrounded by four fluorine atoms and associated with one lone pair of electrons confers an AX4E designated geometry. This molecule has a see-saw shape.