Chem Test Question?

Question

So I had a chem test today and it went really well (I must say that I am pro at the subject). There was one question that confused me, though. What is the difference between a trigonal pyramidal and a tetrahedral molecule? Because I thought they were the same up until the test....Thanks for your help!

Answer 1

A tetrahedral molecule has FIVE atoms in it - one in the center, and four others arranged equally around in a regular pattern. Methane (CH4) is a good example.

A trigonal pyramid has only FOUR. One atom at the apex, and three others forming the base of a pyramid. It's like a tetrahedron with an electron pair instead of one of the atoms. Ammonia (NH3) is a good example.

Answer 2

A tetrahedral molecule has 4 bonding electron pairs. A trigonal pyramidal molecule has 3 bondings electron pairs, and 1 lone electron pair. A lone electron pair is a pair of electrons that is not bonding to anything. When considering bonding and lone pairs, you are supposed to be looking at the central atom of a molecule, which is usually the LEAST electronegative one (hydrogen is an exception).

* Also, a lone electron pair takes up more space than a bonding electron pair. The presence of lone pairs therefore CHANGES the shape of the molecule. More lone pairs means smaller angles between bonding pairs.

Go to this site to learn about the VSEPR theory. Scroll to the bottom to see the difference between the two shapes:

http://en.wikipedia.org/wiki/VSEPR

Answer 3

Trigonal pyramidal has triangles on all sides. Tetrahedral has triangles on all sides except the bottom which is a square.

Answer 4

i believe a tetrahedral has 4 bonding pairs with no lone pairs while a trigonal pyramid only has 3 bonding pairs with one lone pair.

Answer 5

Tetrahedral, atoms are in the vertex and in the center of the pyramid. Example CH4.

Trygonal, atoms are at the vertex only. Example, NH3, BH3

Answer 6

i thought they are the same thing too?
hmm