AP Chemistry : Compounds and Molecules

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

Example Question #16 : Vsepr And Bond Hybridization

What are the bond angles in a molecule of ?

Possible Answers:

The molecule has multiple bond angle measures

Correct answer:

Explanation:

The carbon in the molecule is  hybridized and contains no lone pairs attached to it. This will give the molecule a tetrahedral geometry, standard of a central atom with four single bonds. Bond angles in a tetrahedral molecule are all .

Example Question #14 : Vsepr And Bond Hybridization

Rank the following compounds in order of increasing bond angle:

CO_2, CH_4, SF_6, NH_3, BF_3

If there are multiple bond angles in a single molecule, only consider the smaller bond angle

Possible Answers:

CO_2, \hspace{1 mm}NH_3,\hspace{1 mm} CH_4,\hspace{1 mm} BF_3,\hspace{1 mm} SF_6

SF_6, \hspace{1 mm}BF_3, \hspace{1 mm}CH_4, \hspace{1 mm}NH_3, \hspace{1 mm}CO_2

CO_2,\hspace{1 mm}BF_3,\hspace{1 mm}NH_3, \hspace{1 mm}CH_4,\hspace{1 mm}SF_6

CH_4,\hspace{1 mm} CO_2,\hspace{1 mm} SF_6,\hspace{1 mm} NH_3,\hspace{1 mm} BF_3

SF_6,\hspace{1 mm}NH_3,\hspace{1 mm}CH_4\hspace{1 mm},BF_3,\hspace{1 mm}CO_2

Correct answer:

SF_6,\hspace{1 mm}NH_3,\hspace{1 mm}CH_4\hspace{1 mm},BF_3,\hspace{1 mm}CO_2

Explanation:

CO_2 has two bonding regions and no lone pairs around the central atom, so it has a linear geometry, so its bond angle is 180^{\circ}.

CH_4 has four bonding regions and no lone pairs around the central atom, so it has a tetrahedral geometry with bond angles of 109.5^{\circ}.

SF_6 has six bonding regions and no lone pairs around the central atom, so it has an octahedral geometry with bond angles of 90^{\circ} and 180^{\circ}. For the sake of ranking, we will only consider the smaller angle.

NH_3 has three bonding regions and one lone pair around the central atom, so it has a trigonal pyramidal geometry with bond angles of 107^{\circ}.

BF_3 has three bonding regions and no lone pairs around the central atom, so it has a trigonal planar geometry with bond angles of 120^{\circ}.

 

Example Question #17 : Vsepr And Bond Hybridization

Consider the following reaction, called the Sabatier reaction:

CO_2+4H_2\rightarrow CH_4\hspace{1 mm}+2H_2O

What are the molecular geometries of the products?

Possible Answers:

Square planar and linear

Square planar and bent

Tetrahedral and linear

Tetrahedral and bent

Tetrahedral and tetrahedral

Correct answer:

Tetrahedral and bent

Explanation:

CH_4 has four bonding regions and no lone pairs, so it has a tetrahedral geometry. H_2O has two bonding regions, but it also has two lone pairs, so it has a bent geometry.

Example Question #18 : Vsepr And Bond Hybridization

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 #111 : Compounds And Molecules

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

Possible Answers:

BF3 and H2O

BF3 and NH3

H2O and BeCl2

NH3 and CH4

It is impossible to determine without more information

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 : Vsepr And Bond Hybridization

 is an example of what type of molecular geometry?

Possible Answers:

Seesaw

bypyramidal

Tetrahedral

octahedral

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 #23 : Vsepr And Bond Hybridization

What is the molecular geometry of the  molecule?

Possible Answers:

Trigonal pyramidal

Square planar

Bent

Linear

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.

Example Question #22 : Vsepr And Bond Hybridization

Find the bond angle present in sulfur dioxide.

Possible Answers:

Correct answer:

Explanation:

Sulfur dioxide has the formula  and takes on a trigonal planar electronic geometry, with the two oxygen atoms and the lone pair in the same plane. The molecular geometry will be bent, resulting in a oxygen-sulfur-oxygen bond angle of 120 degrees.

Example Question #25 : Vsepr And Bond Hybridization

Which answer option best approximates the bond angle present in ?

Possible Answers:

Correct answer:

Explanation:

This is the Lewis structure of

Q2

Since the tin atom (Sn) is bonded to two atoms and has one lone pair, the molecule is sp2 hybridized and has a bent, or angular shape. Bent molecules have bond angles of approximately 120°.

Example Question #26 : Vsepr And Bond Hybridization

Which term best describes the molecular geometry of ?

Possible Answers:

Tetrahedral

Trigonal pyramidal

Bent

Trigonal bipyramid

Trigonal planar

Correct answer:

Trigonal pyramidal

Explanation:

This is the Lewis structure of .

Q3

 has three bound atoms and one lone pair, so it is sp3 hybridized and trigonal pyramidal. Note that the electronic geometry (geometry including the lone pair) is tetrahedral, but the molecular geometry (excluding the lone pair) is trigonal pyramidal.

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