AP Chemistry : Molecular and Electronic Geometries

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

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Example Question #21 : Molecular And Electronic Geometries

What is the hybridization state of the central atom in ?

Possible Answers:

Correct answer:

Explanation:

According to hybrid orbital bonding theories, the hybridization state will use a number of orbitals equal to the steric number. The steric number is the number of atoms bonding to the central atom, plus any additional lone pairs.

Nitrogen (N) is the central atom because hydrogen atoms are never central. 

Nitrogen has 5 valence electrons, and in ,  it is bonded with 3 hydrogen atoms, which each borrow one of nitrogen's electrons to create a covalent bond. Subtracting those 3 borrowed electrons from its original 5 leaves 2 left, or 1 lone pair.

In total, the nitrogen atom has 3 bonds and 1 lone pair for a steric number of 4. As a result, its hybridization state must use 4 orbitals. The lowest energy way to do that is to use the lowest energy orbitals that are available. In this case, those are the s and p orbitals. So it uses one s and three p orbitals, giving the sp3 hybridization state. 

Example Question #22 : Molecular And Electronic Geometries

The most similar electronic geometry will be observed between which pair of compounds?

Possible Answers:

It is impossible to determine without more information

BF3 and NH3

H2O and BeCl2

BF3 and H2O

NH3 and CH4

Correct answer:

NH3 and CH4

Explanation:

It is important to note that electronic geometry includes the orientation fo lone pairs, while molecular geometry considers only the geometry of the atoms present in the compound.

Methane, or CH4, has four hydrogen atoms bound to a central carbon, resulting in a tetrahedral geometry.

BF3 has three fluorine atoms bound to a central boron, resulting in a trigonal planar geometry.

Be(Cl)2 has two chlorine atoms bound to a central beryllium, resulting in a linear geometry.

Water, or H2O, has two hydrogen atoms bound to a central oxygen atom with two lone pairs. The molecular geometry is bent, but the electronic geometry is tetrahedral.

Ammonia, or NH3, has three hydrogens bound to a central nitrogen atom with one lone pair. The moelcular geometry is trigonal pyramidal, but the electronic geometry is tetrahedral.

Ammonia, water, and metahne all have the same electronic geometries (tetrahedral), giving us our final answer.

 

Example Question #21 : Molecular And Electronic Geometries

 is an example of what type of molecular geometry?

Possible Answers:

octahedral

Tetrahedral

Seesaw

bypyramidal

Trigonal bypyramidal

Correct answer:

Seesaw

Explanation:

SFhas 6 electron domains coming off of it- 4 F molecules and 2 lone pairs of e. This is an example of see-saw shape.

Example Question #21 : Molecular And Electronic Geometries

What is the molecular geometry of the  molecule?

Possible Answers:

Linear

Square planar

Trigonal pyramidal

Bent

Correct answer:

Trigonal pyramidal

Explanation:

There are three bonding electron pairs around the  central atom and one non-bonding pair, for a total of 4 electron groups. They arrange spontaneously to be furthest apart according to VSEPR theory, which corresponds to when they form a trigonal pyramidal shape.

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