I had problem with the shapes of molecules. How can i
determine it without learning by heart all types of shapes???
Thank you
Guys only like Girls, Guys don't like Guys.
Electrons (negatively charged species) are guys. Due to
inter-Guy (ie. inter-electron) repulsions, electron pairs want to
spread out as far away from each other as possible.
NH3 - For N to have a stable octet but no formal charge, N must
have 1 lone pair and 3 bond pairs. Hence electron geometry =
tetrahedral (since that's the best shape that has 4 electron charge
clouds away from each other as far as possible, but still bonded to
the central atom). Since one of the four electron charge clouds is
a lone pair, ie. treat it as invisible, hence molecular geometry =
trigonal planar.
Do a tripod stand with 3 fingers of your left hand, and use one
finger of your right hand do the 4th and top electron charge cloud,
since lone pairs are invisible, make your right hand invisible by
removing it (although bear in mind the lone pair still remains
there, otherwise the electron geometry would change into trigonal
planar instead of tetrahedral), and what you have left, is called
the molecular geometry, which is trigonal pyramidal.
In future, I recommend you start a new thread on the forum, with
a suitable title eg. "[H2 Chem] - Qn on Chem Bonding", instead of
posting in an old thread such as this one.
Also, if you can afford it, go for tuition sooner rather than
later. Most JC1 students make the mistake of thinking, "I'll try to
handle it myself first, only if I fail the mid year exams, then
I'll look for tuition", which by then, it's a bit too late for the
Promos, bearing in mind you have other subjects to catch up on as
well.
Also, there are many intricacies and aspects to H2
Chem that I have to teach in person, which cannot be
effectively done via an online forum. Regardless, feel free to
continue posting your H2 Chem qns here. I'll reply whatever I
can.
