Chemisty Gcse Revision

[TRshady]

Hi all,
I have a science exam ... tomorrow, lol, so have started revising this moring.
Writing notes though, to memorize I am confused at the differences between four chesmisty terms which I dont think has enough to identify them as difference tihngs. Heres the terms and the definition I have for it:

Molecule: Smallest unit of an element composed of two or more atoms helded together my chemical force.

Element: Substance composed of atoms having an identical number of protons in each nucleus.

Atom: Smallest unit of an element having all the properties of it, positively charged nucleus surround by a system of electrons.

Compound: Substance formed by a reaction of two or more elements joining in proportion of weight.

I know about the atom structure, but have looked around many sites, used google for definitions and more but cant seem to find an explanation, mainly to help me understand what a molecule and compound is, maybe someone who does science in college or university or even someone also doing gcses can help makes the terms clearer for me.

For example, what does it mean by saying proportion of weight in the compound definition? ... that elements of the same mass joining? ...

Thanks for any help.

[Skweeky]

well....give me all those terms and questions in Dutch and I'm sure I can help you out :lol:

Sorry TR, I was pretty good at chemistry in highschool (which is surprising cause I absolutely suck at math :unsure: ), I had the macro-option, which means you really look into it in detail , but it's too difficult to understand. Maybe if you can refrase your question to a more simple structure I can help you out, but I think it'd be better to wait for people like hobbes to come to the rescue

[Proper Bo]

go to the bbc bitesize site, it has everything you need on there.
Aren't they only mocks at this time of year anyway, I didn't revise for mine at all to see how well I'd do and how much revision I'd need to put in for the real one ;)

I can't remember any of the stuff anymore and I only did mine last year :D

[TRshady]

Thanks for the Skweeky and sorry if I never made myself clear.
I have a science exam tomorrow, and need to know what the science words mean, and was hoping someone could explain the differences between them better, especially the words 'compound' and 'molecule' and I'm not sure if thats the right meaning, and if it is then if someone could make it clearer for me then I'd appreciate it.

Your right Proper bo, and although they are mocks, in some ways they are more important and this is the mark which is sent off to college and predict our final grades. I'm using the bitesize site a lot, but if you notice in the chemistry sections, is simply states you should know the meanings, doesn't tell you them. :(

[Proper Bo]

as far as I remember, a compound is made up of different molecules
eg C02 = carbon + oxygen2

[TRshady]

lol, shite ... thats only confused me more so then already.

Any science teachers on this by any chance?
Maybe not teachers then, but this is relatively simply chmestry which everyone should know, care to help a friend? ... or a friend thats could be yours :)

[Proper Bo]

I remember doing my gcse chemistry now, I had a cold and hadn't revised at all, the thingy shells thing really stumped me as I'd missed those in the lessons. I still managed to bluff myself a B for it though :D

The main thing to remember is just relax, you really don't want to be shitting it going into the exam.When you're standing outside the exam hall with your friends just before you go in, DO NOT try and revise! You'll read something which you'll probably instantly forget and really panic. ;)

[Skweeky]

yup, I looked the meaning of those words up in my dictionary and Bo is right, a compound is made out of molecules.

Didn't you ever get that table?

something like metal + hydrogen = bla bla bla (don't know the names for those things in english). Something that ends on OH is an hydroxide, etc...


I think that a compound is for example, an acid, or a base. And they are built up out of several molecules (H2, H2O, F2,...). Although there are some complex compounds that are built out of a molecule and another compound...

Maybe someone else knows what this table is called in english, I'm sure it's easy to find it then. Study that by heart and you'll be alright.

Do you have to make exercices on that test too?

[Rat Faced]

A molecule is the smallest unit of a compound that remains that compound.

If you break molecules of water, for example, into their atoms, you no
longer have water: you have hydrogen and oxygen.

[Proper Bo]

They give you a periodic table (that's its name skweeky ;) ) in the exam, can come in very handy.

FROM BITESIZE:
Elements can combine together to make new substances called compounds.
When iron reacts with sulphur, the iron atoms combine with the sulphur atoms to make iron sulphide.

You can write this as a chemical equation:

Iron + sulphur = iron sulphide
Nice and easy :)

EDIT: Are you doing higher chemistry? If you are, you may want to practice balancing equations, they&#39;re tricky bastards&#33; <_<

[Skweeky]

no Bo, I didn&#39;t mean the periodic table, I meant another one. It&#39;s a small one and it gives you an overview of possible compounds and how they are built

[TRshady]

lol, good advice proper bo and I agree, too much times I&#39;ve done just that, skimming through a whole revision guide, cramming it all in while names are being called in and then sitting down and thinking to yourself "damn ... whats my name?"

Thanks for the replies ... im slowly getting it, keep better explanations coming though, then I&#39;ll write an updated definition which I hopefully undertand.

Edit:

Thanks for the fast replies&#33; ...finding it hard to keep up, lol.
I&#39;m able to balance equatoins and that bite size quote certainly has helped, any chance you could explain the thing about the proportional weight part of the compound definition.

[Gemby!]

i have just had my science exam :)

wasnt too hard - but now i have said that i have probably done bad :P

are you doing a higher paper ?

[TRshady]

Good luck with the results, and yeah, I&#39;m doing higher I&#39;m supposedly "gifted and talented" ... but dont see that much proff of it in me. Though I got 666 in stats in year 6 and have always got top marks in school, it seems all my knowledge is being replaced by what Im learning in web design, if only I could purchase more brain ram, that&#39;ll be here in future though, watch this space ... lol.

[Proper Bo]

Originally posted by TRshady@10 December 2003 - 15:22
any chance you could explain the thing about the proportional weight part of the compound definition.
:blink: no, sorry :blink:

Elements and Compounds
Here are some need-to-know facts about elements and compounds.

There are just over 100 elements. You can find them all in the Periodic Table.
Each element is made of one substance only - the element itself.
There are millions of different compounds.
Compounds are made of different elements joined together.
Compounds are nothing like the elements that they are made from.
The names of some compounds show what they are made of, others are more difficult.

You know how to get the names of the compounds from the elements?
eg
Zinc + Oxygen -------&#62; Zinc Oxide
Iron + Chlorine-------&#62; Iron Chloride
Hydrogen + Sulphur --------&#62;Hydrogen Sulphate
Magnesium + Bromine -------&#62;Magnesium Bromide
etc

[Gemby!]

i done higher - it doesnt ask you anything about compounds and that its more of the balanced equations and waves and stuff like that ;)

well mine was anyway

im only good at biology :)

ooo my brainy stuff is being replaced my my luv for tv and computer and sleep and food and ooo perdy budderfly .... :blink:

[TRshady]

Thanks proper bo, and I do know how to get names of the elements from compounds, I feel pretty confident in this, just though I had it all covered mum comes in, im all smiling and she asks ... "whats a compound then?" ...
Made me think that something which would seem so important, I stumbled on.

Edit: - oh maybe you could help here then gemby.
I take it these appeared in the tests you had? (have you done both papers yet or just the first?) ... the following is what we&#39;ve been told:

paper 1
Chemical Econonmics
Periodic Table
Chemisty
Balance symbol equations
Factors that effect rate of reaction
Different types of reaction eg. oxidation
Exothermic and endorthermic, bond breaking, making etc
Structure of atoms and ions

What scares me is those 6 mark (sometimes higher) questions which if you dont know, can really effect the final mark.

[Proper Bo]

Originally posted by gemby&#33;@10 December 2003 - 15:29
i done higher - it doesnt ask you anything about compounds and that its more of the balanced equations and waves and stuff like that ;)

He&#39;ll have a different paper to you Gemby, if they&#39;re on different days, they&#39;re different papers.
Try This TR (http://www.bbc.co.uk/schools/gcsebitesize/gigaflat/chemistry/compoundsandchemicalchange/compoundsandchemicalchange_quiz.shtml)

[Gemby!]

i think my teachers make them up anyway &#33; :P

i done modules 1-8 by the way so Trshady might have same stuff as me B)

[Rat Faced]

Definite proportions or multiple proportions?

[TRshady]

Thanks Proper bo, done and got 100% in that test.
Im not sure what the modules consist of, but im sure they&#39;ll be quite similar.

[TRshady]

Originally posted by Rat Faced@10 December 2003 - 14:36
Definite proportions or multiple proportions?
Definite proportoins, and explanation would be great, although I understand it, done understand what it means in the compound definition.

[Proper Bo]

Just go through all the tests on that site on the parts you&#39;re unsure about, they really help ;)

[Gemby!]

dont you have module tests and stuff like that ?

[TRshady]

They do and I&#39;ll go through them. Also doing questions in the revision guide I have.
I&#39;m kinda stupid though, always leave revising for the last minute :(, although when started a month early, most of it is forgotten by the time it comes to answer ..

[Proper Bo]

gemby, are you doing the individual sciences or the double award thing? The single ones have longer exams but they&#39;re seperate whereas the double award (which I did) consists of all three subjects being done in one exam.

[Rat Faced]

The same compound always contains the same elements combined together in the same proportion by weight.

According to atomic theory, a compound is formed by the combination of definite number of atoms of different elements. Since each atoms has its own characteristic weight, the relative weight of each component in the compound must always be the same and, therefore, in every pure sample of the same compound, the elements must always be present in the same proportions by weight.

So for example, a molecule of water will always have the same weight as another molecule of water, as the proportions of Hydrogen atoms and Oxygen atoms will be identicle.

[3rd gen noob]

Originally posted by Rat Faced@10 December 2003 - 13:41
So for example, a molecule of water will always have the same weight as another molecule of water, as the proportions of Hydrogen atoms and Oxygen atoms will be identicle.
unless of course, it&#39;s heavy water :)

[Rat Faced]

Heavy water is a different compound :P

[TRshady]

Thanks rat faced :D ... very helpful.
Currently doing some hardcore notes on chemical formulae, i think I have it now, could you tell me how that is different to a molecule please?

[Gemby!]

Originally posted by Rat Faced@10 December 2003 - 14:41
The same compound always contains the same elements combined together in the same proportion by weight.

According to atomic theory, a compound is formed by the combination of definite number of atoms of different elements. Since each atoms has its own characteristic weight, the relative weight of each component in the compound must always be the same and, therefore, in every pure sample of the same compound, the elements must always be present in the same proportions by weight.

So for example, a molecule of water will always have the same weight as another molecule of water, as the proportions of Hydrogen atoms and Oxygen atoms will be identicle.
i got double award BUT we have these things called module tests which we do everytime we learn something about &#39;&#39;atoms and space &#39;&#39; or something like that which eventually goes towards my final grade :)

my final exam conmsists of all the modules - which equal biology physics and chemistry

[Rat Faced]

Originally posted by Rat Faced@10 December 2003 - 14:20
A molecule is the smallest unit of a compound that remains that compound.

If you break molecules of water, for example, into their atoms, you no
longer have water: you have hydrogen and oxygen.
I already told you :P

[3rd gen noob]

Originally posted by Rat Faced@10 December 2003 - 13:45
Heavy water is a different compound :P
well, the molecular and structural formulae for &#39;normal&#39; water and &#39;heavy&#39; water are exactly the same
the only difference is within the hydrogen atoms, so technically, they&#39;re the same compound :P

[Gemby!]

can i just say wow - im actually having a science related conversation - this is a first i think :)

mums gonna be proud &#33;

[Rat Faced]

"Heavy Water" is deuterium oxide.

D2O, as opposed to H2O.......ie a different compound

Deuterium Oxide (http://ptcl.chem.ox.ac.uk/MSDS/DE/deuterium_oxide.html)

[3rd gen noob]

Originally posted by Rat Faced@10 December 2003 - 13:55
"Heavy Water" is deuterium oxide.

D2O, as opposed to H2O.......ie a different compound
i wasn&#39;t aware deuterium was a seperate element

well, you learn something new every day :)

(maybe i was right to give up chemistry)

[Proper Bo]

Could you please not confuse the poor lad with this "heavy water" crap, it has nowt to do with his GCSE at all ;)


EDIT: dear god&#33; Did i just type the word "nowt"? :rolleyes:

[3rd gen noob]

Originally posted by Proper Bo, I tell thee@10 December 2003 - 13:58
Could you please not confuse the poor lad with this "heavy water" crap, it has nowt to do with his GCSE at all ;)
what are you struggling with in particular then? :)

[Proper Bo]

I&#39;m not struggling with anything thankyou, i did my GCSE&#39;s last year :D

[Rat Faced]

Originally posted by 3rd gen noob+10 December 2003 - 14:56--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (3rd gen noob @ 10 December 2003 - 14:56)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-Rat Faced@10 December 2003 - 13:55
"Heavy Water" is deuterium oxide.

D2O, as opposed to H2O.......ie a different compound
i wasn&#39;t aware deuterium was a seperate element

well, you learn something new every day :)

(maybe i was right to give up chemistry) [/b][/quote]
It isnt :P

But we&#39;re talking GCSE here, not BSc ;)

[3rd gen noob]

Originally posted by Proper Bo, I tell thee@10 December 2003 - 14:02
I&#39;m not struggling with anything thankyou, i did my GCSE&#39;s last year :D
oh

i&#39;m in uni just now and i&#39;m not really paying much attention

:">

[3rd gen noob]

Originally posted by Rat Faced@10 December 2003 - 14:03
It isnt :P

But we&#39;re talking GCSE here, not BSc ;)
well, i fell for it :P