Trigonal Bipyramidal Lone Pair Flashcards

Question 1

In an ideal trigonal bipyramid, which pairs of sites make a 90° angle at the center?

Accepted Answer

Every axial–equatorial pair. The two axial sites are 180° apart, and any two equatorial sites are 120° apart.

Question 2

In the VSEPR model, which 90° contact is more repulsive, lone pair–lone pair or lone pair–bonding domain?

Accepted Answer

Lone pair–lone pair. A lone pair generally takes up more space around the central atom than a bonding domain.

Question 3

How many distinct 90° contacts are there across all five sites of an ideal trigonal bipyramid?

Accepted Answer

Six contacts. Pair each of the two axial sites with each of the three equatorial sites.

Question 4

An ideal trigonal bipyramid has one axial lone pair and four bonding domains. How does swapping the lone pair with an equatorial bond change the number of 90° contacts involving that lone pair?

Accepted Answer

The number drops from three to two. The lone pair had three equatorial neighbors at 90° and now has two axial neighbors at 90°.

Question 5

In a trigonal bipyramid, the two axial sites and two equatorial sites carry bonds. What is the molecular shape?

Accepted Answer

Seesaw. The bonded atoms occupy two opposite sites and two sites in the equatorial plane. The remaining equatorial site holds the lone pair.

Question 6

A student counts three 90° neighbors at each axial site and two at each equatorial site. Why does adding those neighbor counts give 12 instead of the number of distinct contacts?

Accepted Answer

Each contact was counted at both ends. Halve 12 to get six distinct 90° contacts.

Question 7

Two lone pairs occupy equatorial sites in an ideal trigonal bipyramid. How many 90° lone pair–bonding domain contacts are there?

Accepted Answer

Four contacts. Each lone pair makes a 90° contact with both axial bonds.

Question 8

A bonded site in an ideal trigonal bipyramid has three 90° neighbors. Two of those neighbors hold lone pairs. How many equatorial lone pairs are there?

Accepted Answer

Two equatorial lone pairs. A site with three 90° neighbors is axial, and all three of those neighbors are equatorial.

Question 9

An ideal trigonal bipyramid has one lone pair. Four of its 90° contacts join two bonding domains. Where is the lone pair?

Accepted Answer

At an equatorial site. Two axial bonds can pair with two equatorial bonds to give four contacts. An axial lone pair would leave only three such contacts.

Question 10

Two lone pairs in an ideal trigonal bipyramid make zero 90° contacts with each other. What are the two possible arrangements by site type?

Accepted Answer

Both could be axial or both could be equatorial. The first layout puts them 180° apart and the second puts them 120° apart.

Question 11

An ideal trigonal bipyramid has one axial lone pair and one equatorial lone pair. How many 90° contacts join a lone pair to a bonding domain?

Accepted Answer

Three contacts. The axial lone pair meets two equatorial bonds at 90°. The equatorial lone pair meets one axial bond at 90°.

Question 12

Why does VSEPR put two lone pairs at equatorial sites in a trigonal bipyramid even though opposite axial sites would put them farther apart?

Accepted Answer

Both layouts avoid a 90° contact between lone pairs. Two equatorial lone pairs make four 90° contacts with bonding domains, compared with six for two axial lone pairs.

Question 13

In a trigonal bipyramid, bonds occupy both axial sites and just one equatorial site. What is the molecular shape?

Accepted Answer

T-shaped. The axial bonds form the straight part of the T, and the equatorial bond projects sideways.

Question 14

A student wants to choose the VSEPR arrangement by minimizing the total number of 90° contacts of all kinds in a trigonal bipyramid. Why can't that pick a layout?

Accepted Answer

The total stays at six whichever sites carry lone pairs. Compare the contact types, giving priority to avoiding 90° contacts between two lone pairs.

Question 15

Exactly two sites in an ideal trigonal bipyramid hold lone pairs. No two bonding domains meet at 90°. What is the lone-pair placement?

Accepted Answer

Both lone pairs are axial. The three bonding domains all lie in the equatorial plane, 120° apart.

Question 16

For two lone pairs in a trigonal bipyramid, a mixed axial–equatorial layout has three 90° lone pair–bond contacts and one 90° contact between lone pairs. The all-equatorial layout has four 90° lone pair–bond contacts and zero contacts between lone pairs at 90°. Which layout does VSEPR favor?

Accepted Answer

The all-equatorial layout. Avoiding the 90° contact between lone pairs takes priority over saving one 90° lone pair–bond contact.

Question 17

Start with two equatorial lone pairs in an ideal trigonal bipyramid. Swap one of them with an axial bond. What happens to the number of 90° contacts between two bonding domains?

Accepted Answer

It stays at two. Before the swap, two axial bonds meet one equatorial bond at 90°. After it, one axial bond meets two equatorial bonds at 90°.

Question 18

With three lone pairs in a trigonal bipyramid, why does VSEPR favor putting all three in the equatorial plane?

Accepted Answer

That is the only layout with zero 90° contacts between lone pairs. Any other three-site layout puts lone pairs in both site types, creating 90° lone pair–lone pair contacts.

Question 19

An ideal trigonal bipyramid has three lone pairs and exactly one axial bond. What is the angle between the two bonds in that hypothetical layout?

Accepted Answer

90°. The second bond must occupy an equatorial site, so the two bonds use different site types.

Question 20

In an ideal trigonal bipyramid, three lone pairs occupy one axial site and two equatorial sites. How many 90° lone pair–lone pair contacts do they make?

Accepted Answer

Two contacts. The axial lone pair meets each equatorial lone pair at 90°. The two equatorial lone pairs are 120° apart.

Question 21

In an ideal trigonal bipyramid, four 90° contacts join two bonding domains and none joins two lone pairs. How many 90° contacts join a lone pair to a bonding domain?

Accepted Answer

Two contacts. There are six distinct 90° contacts altogether, so subtract the four contacts between bonding domains.

Question 22

Two hypothetical trigonal bipyramids each contain three lone pairs. In one, the two bonds are both equatorial. In the other, one bond is axial and one is equatorial. Which layout has more 90° lone pair–bonding domain contacts?

Accepted Answer

The layout with both bonds equatorial has four, compared with three for the mixed layout. With both bonds equatorial, each meets two axial lone pairs at 90°.

Question 23

All three equatorial sites of a trigonal bipyramid hold lone pairs. Why do the remaining bonds give a linear molecular shape?

Accepted Answer

The two bonds occupy opposite axial sites, 180° apart. The molecular shape follows the bonded atoms.

Question 24

A seesaw molecule is modeled by placing one lone pair on an equatorial site. Does the 120° angle between the remaining equatorial sites predict their exact measured bond angle?

Accepted Answer

No. The 120° value comes from the ideal trigonal bipyramid. Real bonding domains can shift when the lone pair repels them.

Question 25

In an ideal trigonal bipyramid, lone pairs occupy sites P and Q, which are 120° apart. A bond at site R is 90° from both. What type of site is R?

Accepted Answer

Axial. The 120° angle places P and Q in the equatorial plane. Only an axial site makes a 90° angle with both.

Question 26

An ideal trigonal bipyramid has exactly three lone pairs. Two 90° contacts join lone pairs to each other, and three join lone pairs to bonding domains. How many axial sites hold lone pairs?

Accepted Answer

One axial site holds a lone pair. A layout with two axial lone pairs would also have two 90° contacts between lone pairs, but it would have four 90° lone pair–bonding domain contacts.

Question 27

A five-domain model shows a lone pair on one equatorial site and bonds on the other four sites. A student calls the molecular shape trigonal bipyramidal because five sites are occupied. What did they count incorrectly?

Accepted Answer

They counted the lone-pair site as part of the molecular shape. All five domains determine the electron geometry, while the four bonded sites give a seesaw molecular shape.

Question 28

Every 90° contact in an ideal trigonal bipyramid is between a lone pair and a bonding domain. If the total number of lone pairs is unknown, what two layouts fit?

Accepted Answer

Either both axial sites hold lone pairs and all equatorial sites hold bonds, or all three equatorial sites hold lone pairs and both axial sites hold bonds. Each axial–equatorial pair has one site of each kind.

Trigonal Bipyramidal Lone Pair Flashcards

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Trigonal Bipyramidal Lone Pair Flashcards

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