IGCSE Edexcel Chemistry 19th May 2016

Hi guys.
I have problems answering questions related to bonding. Please help.

erm, have you tried bitesized? Bonding in what sense, like, drawing out the bonding, or the properties of certain types of bonding?

what type of bonding questions?

Questions regarding why some compounds have a higher melting point than others.

For example: stating why water has a much lower melting point than sodium oxide.My answer to that would be that water is a polar molecule formed by a covalent bond and sodium oxide is formed by an ionic bond. And my teacher wouldn't give me a singe mark for that question. Why?

what I would recommend is to look at the mark schemes and just copy the way the examiner wrote it(that's what I did for the exam). Do you have the CGP book?

Hi,

Water has a lower melting point because it is a simple covalent molecule, and so consists of weak intermolecular bonds, which break at low temperatures.

Sure I will do that. Uhmm no I don't have the CGP book

the cgp book really helps try searching for similar questions and you should be fine! Good luck with you exam!

Sure I will look for them. Thank you and good luck to you too.

Hi Prishita,

Water has hydrogen bonding, not covalent bonding. And yes you are right about the ionic bonding. Sodium has a + charge and oxygen has a 2- charge and so they are strongly attracted to each other. Also, remember that when you are given two molecules, use comparatives such as stronger - that way you will be able to gain maximum marks

Hi,
Thank you for the answer, however I still I have a question. what is the difference between a covalent bonding and hydrogen bonding. I haven't heard of that before, because as much as I know in water the hydrogen and oxygen atoms share the electrons.

Hi,
Thank you for the answer, however I still I have a question. what is the difference between a covalent bonding and hydrogen bonding. I haven't heard of that before, because as much as I know in water the hydrogen and oxygen atoms share the electrons.

Hi, I'm sorry! I do a-level chemistry and so went in-depth with the bonding
Anyway, to answer your question, (btw dw if you don't understand this, it's way too much knowldege for an IGCSE student) Hydrogen bonding is the bonding that occurs between hydrogen and 3 other molecules (fluorine, oxygen and nitrogen). Since water contains both hydrogen and oxygen, it has hydrogen bonding.

But you do not need to know that for your exam. And you are right, H2O has covalent bonding so dw.

I guess the way you have structured your answer might have been different to the one that your teacher wants. So here is an example of how you can answer it:
H2O has covalent bonding which less stronger compared to the ionic bonding in sodium oxide. That is why less energy is needed to break the covalent bond in H2O and so the melting point is lower

A hydrogen bond is the attractive force between the hydrogen attached to an electronegative atom of one molecule and an electronegative atom of a different molecule. Usually the electronegative atom is oxygen, nitrogen, or fluorine, which has a partial negative charge.

That's alright.
Thank you for the answer I will definitely use the sample answer you provided.

Woahh, that sounds hard. I guess that's A-level right?
Anyway thanks for the answer.