Molecular Shapes: The AXE Method, Part 1 (10.1.5) Flashcards
• Every molecule has an AXE designation that provides information about the number of atoms and lone pairs of electrons surrounding the central atom.
• Every molecule has an AXE designation that provides information about the number of atoms and lone pairs of electrons surrounding the central atom.
• By determining the AXE designation of a molecule, the molecular geometry and bond angles can also be determined.
• By determining the AXE designation of a molecule, the molecular geometry and bond angles can also be determined.
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.
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.
AX2 molecules include a central atom surrounded by two
other atoms and having no lone pairs of electrons. Molecules with an AX2 designation have a linear geometry and a bond angle of 180º. Examples of AX2 molecules are beryllium hydride and carbon dioxide. AX3 molecules include a central atom surrounded by three other atoms and having no lone pairs of electrons. Molecules with an AX2 designation have a trigonal planar geometry and a bond angle of 120º. Examples of AX3 molecules are boron trifluoride, nitrate ion, and formaldehyde.
AX2 molecules include a central atom surrounded by two
other atoms and having no lone pairs of electrons. Molecules with an AX2 designation have a linear geometry and a bond angle of 180º. Examples of AX2 molecules are beryllium hydride and carbon dioxide. AX3 molecules include a central atom surrounded by three other atoms and having no lone pairs of electrons. Molecules with an AX2 designation have a trigonal planar geometry and a bond angle of 120º. Examples of AX3 molecules are boron trifluoride, nitrate ion, and formaldehyde.
AX2E molecules include a central atom surrounded by two
other atoms and having one lone pair of electrons. Molecules
with an AX2E designation have a bent geometry and a bond
angle of less than 120º. Examples of AX2E molecules are
sulfur dioxide and ozone.
AX4 molecules include a central atom surrounded by three
other atoms and having no lone pairs of electrons. Molecules
with an AX4 designation have a tetrahedral geometry and a
bond angle of 109.5º. Examples of AX4 molecules are silane,
methane and carbon tetrachloride.
AX2E molecules include a central atom surrounded by two
other atoms and having one lone pair of electrons. Molecules
with an AX2E designation have a bent geometry and a bond
angle of less than 120º. Examples of AX2E molecules are
sulfur dioxide and ozone.
AX4 molecules include a central atom surrounded by three
other atoms and having no lone pairs of electrons. Molecules
with an AX4 designation have a tetrahedral geometry and a
bond angle of 109.5º. Examples of AX4 molecules are silane,
methane and carbon tetrachloride.
AX3E molecules include a central atom surrounded by three
other atoms and having one lone pair of electrons. Molecules
with an AX3E designation have a tetrahedral geometry and
a bond angle of slightly less than 109.5º. Examples of AX2E
molecules are ammonia and thionyl chloride.
AX2E2 molecules include a central atom surrounded by three
other atoms and having one lone pair of electrons. Molecules
with an AX2E2 designation have a bent geometry and a bond
angle of less than 109.5º. Examples of AX2E2 molecules are
water, and sulfur dioxide.
The rules for AXE designations can be applied to any
non-terminal atom in a molecule.
AX3E molecules include a central atom surrounded by three
other atoms and having one lone pair of electrons. Molecules
with an AX3E designation have a tetrahedral geometry and
a bond angle of slightly less than 109.5º. Examples of AX2E
molecules are ammonia and thionyl chloride.
AX2E2 molecules include a central atom surrounded by three
other atoms and having one lone pair of electrons. Molecules
with an AX2E2 designation have a bent geometry and a bond
angle of less than 109.5º. Examples of AX2E2 molecules are
water, and sulfur dioxide.
The rules for AXE designations can be applied to any
non-terminal atom in a molecule.
What is the AXE designation for the ammonium ion?
AX4 (D)
The ammonium ion has four hydrogen atoms bound to it and no lone pairs of electrons associated with the central atom. The ammonium ion has an AX4 designated geometry.
Which of the following compounds has an AX2E designated geometry?
sulfur dioxide (C)
Sulfur dioxide, SO2, has the following Lewis dot structure:
The central atom is surrounded by two atoms and has one lone pair of electrons, thus sulfur dioxide has an AX2E designation.
What is the I–Al–I bond angle in the aluminum iodide molecule?
120º (B)
What is the expected bond angle for a molecule with an AX2E designation?
120º (B)
Any molecule that has an AX2E designation will have a bond angle very close to 120º.
Which of the following is not an AX3 designated geometry?
PCl3 (D)
Which of the following compounds would have a 120° bond angle?
NO3- (D)
What is the F–As–F bond angle in the arsenic trifluoride molecule?
about 109.5º (C)
Which of the following compounds is listed with an incorrect AXE designation?
NO3-, AX3E (C)
The nitrate ion does not have a lone pair of electrons on the central atom. The nitrate ion has an AX3 designated geometry.
What is the AXE designation for aluminum chloride?
AX3 (D)
The central atom is surrounded by three atoms and has no lone pairs, thus the AXE designation is AX3.
