I have a list of Materials, and I need to Write Their Molecular geometry by theory VSEPR .
This is the list:
1) H2Te the Shape here is an linear Because there is 2 Bonding Electron Pairs
2) H2CO the Shape here is an trigonal planar Because there is 3 Bonding Electron Pairs
3)PBr2F the Shape here is an trigonal planar Because there is 3 Bonding Electron Pairs
4) CS2 the Shape here is an linear Because there is 1 Bonding Electron Pairs
5)SiCl4 Shape here is an tetrahedral Because there is 4 Bonding Electron Pairs

Do I correct ? If not so what is the best way to know the Molecular geometry ?
Thanks.

1) No, the shape is bent, or, non linear.

Terrulium has 6 outermost electrons, 2 of which will participate in bonding, leaving 2 pairs of lone electrons (4 in all). Those lone pairs will repel each other and at the same time, repel the bonded pairs and force them to bend.

Another way of looking at it is to notice that Te is in group 6, and just like water, H2O is bent, H2Te will also be bent.

2) Right, and there are no lone electrons about to repel any of the bonded pairs.

3) No to this one. P has 5 outermost electrons and Br and F both form single bonding. Since there is 2 Br and 1 F, 3 electrons from P will be bonded, leaving 2 behind. Those, as explained in 1 will push the bonded pairs. The resulting shape is a triangle based pyramid.

4) Right, but the reason is not convincing. The S will bind to the C atom via a double bond and since there are two S and the C atom has 4 outermost electrons, there will be no lone electrons and the shape will be linear.

5) The shape is indeed tetrahedral, but again, not because of the number of bonding electron pairs. Si has 4 outermost electrons and each will contribute to bonding, meaning that there are no lone electrons. In that case, the most stable shape becomes tetrahedral.

Here are pictures that may help you. This is how I work the shapes out. (Sorry if it's big)

General electronic configuration of outermost electrons, then the structure showing bonded and lone pairs of electrons and lastly the shape produced. [Note: I'm using cross as being the electron of the central atom and dots for the electrons of the other atoms]

http://p1cture.me/images/88587605974756647991.png

As you can see, I sort of a little exaggerated the lone pairs because they repel much more than bonded pairs and hence affect the shape a lot.

Amazing answer!!

Thanks really much.