Question

Recheck

Answer 1

VSEPR theory and molecular shapes

The order is trigonal pyramidal, tetrahedral, trigonal planar, bent.

NI₃

NI₃ is trigonal pyramidal (see Figure 1).

Think of a trigonal pyramid as a three-legged stool, with the “central” atom (N) as the seat. The three iodine atoms form the feet of the stool.

If you close in all the sides of the figure, you have a trigonal (triangular) pyramid, i.e., a pyramid with a triangular base).

CCl₄

CCl₄ is tetrahedral (see Figure 2).

A tetrahedron is also a pyramid with a three-cornered base. The difference is that the central atom (C) is buried in the middle of the figure and all sides have the same length.

The three sides plus the base make four identical sides (tetra = four + hedra = faces) that are equilateral triangles.

BF₃

BF₃ is trigonal planar (see Figure 3).

It is flat, sort of like a slice of pizza. The three bonds point to the corners of an equilateral triangle.

NO₂⁻

NO₂⁻ is a bent molecule.

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Unit conversions

You want to convert miles per hour ⟶ kilometres per hour.

Convert miles to kilometres.

1 mi = 1.61 km                     Do the conversion.

99 × 1.61/1 = 160 km/h  

Convert hours to minutes.

1 h = 60 min                        Do the conversion

159 × 1/60 = 2.7 km/min  

Note: The answers can have only two significant figures because they all depend on the original speed (99 mph = two significant figures).  

Answer 2

How to Tell Lewis Diagrams apart

Trigonal planar, Trigonal pyramid both have 3 things attached to them. Not 4. Tetrahedral is the only Lewis Diagram's center piece that has 4 things attached to it.

Tetrahedral: C with 4 Cl's attached.

Trigonal Planar: is flat. The element in the middle is generally a metal or an element from the Left side of the periodic table. There is never an isolated pair of electrons with Trigonal Planer shapes. Summary:

• The center element is a Metal on the left side of the periodic table.
• In your example, Boron is at the center of the drawing and it is in column 2 of the periodic table which makes it a metal.
• There are no isolated electron pairs

Trigonal Pyramid

• The two electrons are circled. These two are isolated and nothing is attacted to them.
• The central element is a non metal -- Nitrogen in this case.
• The non metal is on the RIGHT side of the periodic table

Bent

• Looks like it is in a straight line (but it is not).
• There are usually double bonds involved.
• The angle formed is usually greater than 90 degrees
• The central element is usually a non metal.

Problem One

Both parts of this question are correct.

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