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

Sorry TR, I was pretty good at chemistry in highschool (which is surprising cause I absolutely suck at math ), 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

[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

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're tricky bastards!