Wednesday, October 3, 2007

Chemistry Questions - Bonding / Organic Chemistry

Hey students,

Try this O Level Chemistry questions on Bonding and Organic Chemistry.

Q) The number of shared pairs electrons in a molecule of methanol is:
A) 3
B) 4
C) 5
D) 6

Show me your reasoning.


Qn answered and explained under comments


zhengning said...

Hey hello there!
I'm an O level student too, Chanced upon this blog and decided to do the Qns here, cool blog you have here to provide help for students like myself Haha, Thanks for setting up this blog!

Anyway, i think the Ans for this Qn is (C), correct me if I'm wrong.

By drawing the structure of Methanol, CH3OH, We can see that 3 H atoms and the C atom, each share it's electrons with one another. So there are 3 pairs of electrons shared already.

However, the C atom is bonded to the O atom, and a pair of electrons is shared here, making C obtaining a stable structure. O and H atom, itself, will share one pair of electrons so obtain a stable structure as well.

Hence, 5 pairs of electrons are shared....
Am i right? Lol. Not very confident of my own answer, haha.

Sean Chua said...

Hey Zhengning,

Most welcome. It's our pleasure to be able to help students that are preparing for their O Levels in less than a month time.

Always Lovely which is a expert in A-Math Coaching for more than 9 years (or maybe longer i think), has convinced me to come together to build up this blog to help students. We are glad that the response is good and students and parents alike are finding this platform helpful to them.

Back to the question, you are Absolutely SPOT ON! You have good grasp of Chemistry Concepts. Keep up the good work!

PS: For those that don't understand how Zhengning come to the answer, do let me know so that i can scan and upload the answer with diagrams.


robobooga said...

hmm.. is the answer to this qn (C)?

By drawing the CH3OH structural formula, C will share 4 pairs of electrons with 3H and O.. while O will share yet another pair of electrons with the remaining H... therefore, there should be 5 pairs rite?

Anonymous said...


Sean Chua said...

I do not have access to a scanner at the moment.

Draw out the Full Structural Formulae of Methanol, CH3OH. Since this is a covalent molecule, link all element present using a straight line (i,e. covalent bond). In this way, you can see that there are 5 straight lines in the molecule, i.e. 5 pairs of electrons.

PS: You can follow Robobooga depiction to draw out the molecule.