The Student Room Group

Shape of molecule help please!!

How do I draw the shape of TlBr3 (2-)
Draw the dot-cross electron structure (Lewis structure) showing the where the electrons are coming from. Also take note of the 2- charge.
Reply 2
pryamidal: tetrahedral with lone pair at the top, 107 degree angle
Original post by sumayyah99
How do I draw the shape of TlBr3 (2-)


Tetrahedral I think
Reply 4
Original post by BTAnonymous
Draw the dot-cross electron structure (Lewis structure) showing the where the electrons are coming from. Also take note of the 2- charge.

Why is it not tetrahedral if there are 3 electrons in outer shell of Tl and Br3 will share one electron each with Tl. Where does the lone pair come from?
Reply 5
Original post by memebois
pryamidal: tetrahedral with lone pair at the top, 107 degree angle


Hey how did you get to that please because I'm not sure how its that shape and where the lone pair came from?
Original post by sumayyah99
Why is it not tetrahedral if there are 3 electrons in outer shell of Tl and Br3 will share one electron each with Tl. Where does the lone pair come from?


Well if there was no lone pair, it still wouldn't be tetrahedral! Remember, 3 lone pairs would be a trigonal planar shape (120 degrees).

The 2- indicates that the Ti atom has gained 2 electrons, so it has a lone pair of electrons. Yes, each Br will share one electron with the Ti but the 2 electrons which have been gained are unpaired.

So the shape is not tetrahedral but triangular pyramid.
Reply 7
the lone pair comes from the fact its a 2- ion (2 extra electrons)
Tl is in group 3 so it has 3 electons in outer shells which form bond pairs with the bromines
heres a lil diagram :smile:
Reply 8
Original post by memebois
the lone pair comes from the fact its a 2- ion (2 extra electrons)
Tl is in group 3 so it has 3 electons in outer shells which form bond pairs with the bromines
heres a lil diagram :smile:


Ah thanks so much:smile: Im also struggling with drawing TlCl4 (3-) any idea how to draw that one because I'm not sure how 3 extra electrons can be added on.
Reply 9
Original post by BTAnonymous
Well if there was no lone pair, it still wouldn't be tetrahedral! Remember, 3 lone pairs would be a trigonal planar shape (120 degrees).

The 2- indicates that the Ti atom has gained 2 electrons, so it has a lone pair of electrons. Yes, each Br will share one electron with the Ti but the 2 electrons which have been gained are unpaired.

So the shape is not tetrahedral but triangular pyramid.


Oh yeah lol stupid mistake. Great, thank you it makes sense now!:smile:
Original post by sumayyah99
Oh yeah lol stupid mistake. Great, thank you it makes sense now!:smile:


np :]
Reply 11
Original post by BTAnonymous
np :]


Any ideas how you would draw TlCl4(3-) pls. Can't seem to figure out how to add 3 extra electrons to the shape??
Original post by sumayyah99
Ah thanks so much:smile: Im also struggling with drawing TlCl4 (3-) any idea how to draw that one because I'm not sure how 3 extra electrons can be added on.


so Tl is in group 3, stick to the center atom first. You have 3 electrons, and 4 chlorines to share those with. So you're left with 1 chlorine as the odd one out. Now you add on the 3 extra electron - one goes to bond with the final chlorine, and the other two electrons form a lone pair! So 4 bond pairs and a lone pair (forgot the shape, think its T shaped?) hope that helps x
Reply 13
Original post by memebois
so Tl is in group 3, stick to the center atom first. You have 3 electrons, and 4 chlorines to share those with. So you're left with 1 chlorine as the odd one out. Now you add on the 3 extra electron - one goes to bond with the final chlorine, and the other two electrons form a lone pair! So 4 bond pairs and a lone pair (forgot the shape, think its T shaped?) hope that helps x

Thank you, you're a lifesaver! :yy::h:
Draw a Ti atom with 3 electrons in it's outer shell. Add the 4 Cl atoms showing the electron which they donate and share in the covalent bond. You should encounter a problem in that there's 4 Cl atoms but only 3 outer shell electrons, so you can only form 3 Cl-Ti bonds right?

Now add the 3 extra electrons.

One of these 3 extra electrons can now form the final (4th) Cl-Ti bond, thus we are left with a lone pair as well.

A common misconception is that you can only have 8 electrons in the outer shell; that's GCSE. We now consider the orbitals and Ti's vacant orbital (outer orbital) is a d orbital which can hold 10 electrons.

Are you sure it's TiCl4 (-3) though? I'm not sure that exists, lol.
That is why I have been struggling with shapes of molecules due to this misconception

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