i have my gcse exams coming up in november (if you know what they are because the levels are different in different countries etc :S) and i struggle with chemistry :(
i got a letter home from schol telling my parents that i was under-acheiving in chemistry :S
i just dont understand some of it :(
Kirsty, don't rant, stay calm. That is easy for me to say because I "can do" chemistry. Pick one topic that you find difficlt and focus on that one. Reply on here once you have picked te first one to go for.
You probably know that the English and Scottish exam systems are different and although I know a bit about the Scottish one, I am more familiar with the English one so you will need to help me with the details.
I am assuming that you have not done any SQA exams before and that you are probably in the fourth year of secondary school.
Do you have a SQA exam coming up really soon or is it just that you realise you have a few problems and want to get them sorted out in good time?
Have you always found Chemistry difficult or has just got difficult in the past few months?
Do you have a syllabus or specification that lists all the things you are supposed to know for the exams?
Do you have a textbook that goes with the course you are doing?
While you are thinking about those questions, have a look at this revisionworld page
and see if you understand it. If you do, click on the link at the bottom to move on to the next one in th series. Do this slowly and only move on if you are happy hat you understand EVERYTHING on the page. If there is a problem (even a small one), come back on here and let m know. We can the try to sort it out.
yes, i am in fourth year at secondary.
i have SQA exams in may but first i have estimate exams in november.
i have always found chemistry difficult! i just dont understand it and its extremely hard to remeber everything for my exams :(
""Do you have a syllabus or specification that lists all the things you are supposed to know for the exams?"".....EVERYTHING i have learnt in the last 4years :( so basically everything about chemistry :S
""Do you have a textbook that goes with the course you are doing?""...we dot have textbooks, we write our OWN notes and the questions we answer are made up on the spot by our teacher as examples. i DO have Leckie standard grade chemistry books tho :) but i think i need MORE help than that :S
Thank You SOOOOO much for all your help :D im extremely greatful :D
OK, let's get started. I don't want to try to confuse you even more by teaching you things out of sequence, so it is better to try to look at something you have already done and found difficult.
Try to tell me JUST ONE thing you cannot do at the moment. If you can't think of one for yourself, have a look at this index page
and choose a topic to start with. It might be something you are really scared of now or it might be something that you almost understand. The choice is yours.
If you still can't think of one for yourself, try this one.
It might seem like a huge task but you have made the right start by trying to do something now. Remember that the only way to eat an elephant is one bite at a time.
As soon as you can, ask your teacher to give you a copy of the syllabus (or you might call it a specification) so that you know what you have to work towards.
Have a look at this too. Which of these questions do you find easy, difficult or impossible?
Covalent bonding:
The aim is for each of the atoms to end up with a full outer shell of electrons. For most atoms, that means eight electrons but for some very small atoms (hydrogen and helium) it only needs two elctrons.
A molecule like ammonis (NH3) has a nitrogen atom at the centre which has five electrons in its outer shell.
Deal with each hydrogen in turn. A hydrogen atom puts its one electron in for sharing. One of the nitrogen's atoms is used for sharing. Hydrogen now has a share in two electrons and so is happy. Nitrogen now has a share in six electrons. This is not a complete shell so more needs to be done.
We can bring in another hydrogen with its one electron available for sharing. The hydrogen ends up sharing two electrons and so is happy. The nitrogen now has seven electrons. Better, but still not quite there. Let's use yet another hydrogen atom (to make three altogether).
This now means that the nitrogen has a share in eight electrons (the three it has gained a share in from the hydrogens, the three it has given to be shared with hydrogen and the two it has not used for bonding). Three + three + two = eight.
See if this makes sense and then get back to me for more help....either harder examples or a simpler explanation if you need it.
OK then. let's think about the dartboard idea for a moment. At the centre (bullseye) is the nucleus. It contains the protons and any neutrons that the atom has. The electrons are arranged around this in shells. The first shell can have a maximum of two electrons. Outside this, the second shell can have a maximum of eight electrons. Outside that one there is another shell with a maximum of eight electrons.
We often write the electron arrangement as a set of numbers. For example, if I have the element sodium (11 electrons altogether) I would need 2 in the first shell, 8 in the second shell and then the last one in the third shell. I coyuld write this as 2,8,1.
Does this make sense? Let me know and then we can move on.
Think of sodium (atomic number 11 and so electrons are 2,8,1). It can have an empty outside shell by losing one electron. Since it is losing a negative charge, it becomes a one-plus ion.
Think of chlorine (atomic number 17 and so electrons are 2,8,7). It can have a full outside shell by gaining one electron. Since it is gaining a negative charge, it becomes a one-minus ion.
If you think about it, a full outside shell and an empty outside are really the same thing...it just depends on which shell you are talking about.
The sodium one-plus is attracted to the chlorine one-minus. That makes sodium chloride.
The rule is simple:
Metals lose enough electrons to give them an empty shell. The ion they make is as positive as the number of electrons they have lost.
Non-metals gain enough electrons to give them a full shell. The ion they make is as negative as the number of electrons they have gained.
The only tricky bit now is to decide how many positive ions go with how many negative ions. Simply make sure that the total of positive charges matches the total of negative charges. (eg 2 x 3+ ions can match 3 x 2- ions).
Bonding is all about putting electrons into a more stable arrangement. It is a bit like a ball at the top of a hill being allowed to run down the hill to the bottom. The electrons in the shells in the atoms are fairly stable but a better arrangement can be found. If you have some metal atoms and some non-metal atoms, a better arrangement is often to move one or more electron(s) from the metal to the non-metal.
If the electron arrangement in the metal is 2,8,1 we can move the electron from the outsde shell to the non-metal. Losing an electron (which is negative) makes the atom into a positive ion.
When the electron joins the non-metal atom, it forms a negative ion.
The rule to decide how many electrons leave the metal atom is "REMOVE ENOUGH ELECTRONS TO LEAVE AN EMPTY OUTSIDE SHELL".
The rule for the non-metal atom is "ADD ENOUGH ELECTRONS TO GIVE A FUL OUTSIDE SHELL".
So sodium (2,8,1) loses 1.
Chlorine (2,8,7) gains 1.
The sodium 1+ ion attracts the chloride 1- ion. They form an ionic crystal lattice.
If you have a magnesium atom (2,8,2) it can lose two electrons. It forms a 2+ ion.
If you have an aluminium ion (2,8,3) it can lose three electrons. It forms a 3+ ion.
If you have an oxygen atom (2,8,6) there is room for two more electrons in the outside shell. It will gain th two electrons to form a 2- ion.
The final bit about deciding how many of each kind of ion stick together is easier to understand than it is to explain.
Once you have decided what kind of ions you have got, simply take enough positive ions and negative ions to make sure that the overall charge is zero. Here are some examples.
magnesium 2+ and chloride 1-
You need two chlorides to cancel out the magnesium.
sodium 1+ and oxide 2-
You need two sodiums to cancel out the oxide.
As always, have a look at this and let me know what you can and can't understand
i did my chemistry general and credit chemistry exams today!!!
mg! they were soooooo difficult!
i revisied so much and my mind went completely blank in the exam! the questions were imposible!!!
This may sound silly, but whatever you did yesterday is now in the past and does not matter. What you need to concentrate on now is working hard towards your next exam. If you start now, there will be many days to study each topic. If you leave it until later, there will be less and less time.
The other thing to think about is the possibility of a resit. Does your school allow this? If it does, find out about how to re-enter and when the resit will be.
If you found some of our e-conversations useful, try another topic and see if I can help there too.
You will find it so much easier to revise if there isn't the panic of an urgent exam.
The idea is that the metal atom wants to lose any electrons in its outside shell. Sodium has 2,8,1 so loses the 1. Magnesium has 2,8,2 so loses the 2.
This means that sodium forms a 1+ ion and magnesium forms a 2+ ion (remember that electrons are negative so when you lose one you become more positive).
Non-metals want to gain electron(s) to fill up the outside shell. Chlorine is 2,8,7 and wants to become 2,8,8. It gains one electron and forms the chloride 1- ion. Oxygen is 2,6. It has two spacers in the outside shell and so gains two electrons to form the oxide 2- ion.
See if this makes sense and then we will stick the ions together.
sodium chloride needs to have one sodium ion and one chloride ion because the 1+ charge of the sodium is cancelled out by the 1- charge of the chloride. The formula is NaCl.
Magnesium chloride needs to have one magnesium ion and TWO chloride ions because the 2+ charge of the magnesium is not cancelled out by the 1- charge of one chloride ion. Two chloride ions (2 x 1-) is enough. The formula is MgCl2. (sorry I can't do the "little 2" on the website).
Magnesium oxide needs to have one magnesium ion and one oxide ion because the 2+ charge of the magnesium is cancelled out by the 2- charge of one oxide ion. The formula is MgO.
Sodium oxide needs to have TWO sodium ions and only one oxide ion because the 1+ charge of a single sodium ion is not enough to cancel out the 2- charge of the oxide ion. Two sodium ions (2 x 1+) is enough. The formula is Na2O. (sorry, again, I can't do the "little 2" on the website).
If you can do this, you have understood the bonding part of the ionic theory. If you can, great, if not, get back online and let me know. The next stage is to see what happens when millions of these ions get together to form a crystal.
Imagine a sodium (+) ion next to a chloride (-) ion. If we put another sodium ion in place, the best place for it would be close to the chloride ion and as far as possible from the sodium ion. That way we would maximise the attractive forces between + and - ions but minimise the repulsion forces between the two + ions. Something like this:
Na Cl Na
The next chloride would join:
Na Cl Na Cl and so on.
Another good way to join the ions would be to have the two sodiums and two chlorides in a square with the sodium ions at opposite corners:
Na Cl
Cl Na
and we could keep that patern going since we have short distances between the opposite charge ions and a long distance (across the square) between the same charges.
Taking it even further we could have a cube with the same kind of pattern.
It would have a
Na Cl
Cl Na square on top of a
Cl Na
Na Cl square.
Again keeping the same charged ions as far apart as possible and the opposite charged ions as close as possible.
If you do the same thing with a few million million ions and you have a crystal.
n e 1 no n e good ways to revise chemistry
Yes! What level are you studying?
Reply and I will give some suggestions.
i have my gcse exams coming up in november (if you know what they are because the levels are different in different countries etc :S) and i struggle with chemistry :(
i got a letter home from schol telling my parents that i was under-acheiving in chemistry :S
i just dont understand some of it :(
can you help me please?
lisa xx
I will try to help. Try to take one step at a time. Reply with one topic that you are coinfident about and one that you are finding difficult.
Also, which exam board are you working towards?
[rant]
i don't get chemistry either im currently studying 4 GCSEs and i havent got a clue about chemistry xx
[/rant:(
Kirsty, don't rant, stay calm. That is easy for me to say because I "can do" chemistry. Pick one topic that you find difficlt and focus on that one. Reply on here once you have picked te first one to go for.
thanks
erm...i think its SQA
and im practically struggling in EVERYTHING lol. im not good at ANY of the chemitry course :(
x
If you are doing SQA exams, I think it would be good for you to look at these websites.
This bit is "Services for learners"
http://www.sqa.org.uk/sqa/23564.html
and this was published in te Herald in 2007.
http://www.sqa.org.uk/files_ccc/Exam_Guide_2007_Chemistry.pdf
You probably know that the English and Scottish exam systems are different and although I know a bit about the Scottish one, I am more familiar with the English one so you will need to help me with the details.
I am assuming that you have not done any SQA exams before and that you are probably in the fourth year of secondary school.
Do you have a SQA exam coming up really soon or is it just that you realise you have a few problems and want to get them sorted out in good time?
Have you always found Chemistry difficult or has just got difficult in the past few months?
Do you have a syllabus or specification that lists all the things you are supposed to know for the exams?
Do you have a textbook that goes with the course you are doing?
While you are thinking about those questions, have a look at this revisionworld page
http://www.revisionworld.com/gcse/chemistry/classifying-materials/atomic-structure/history-atom
and see if you understand it. If you do, click on the link at the bottom to move on to the next one in th series. Do this slowly and only move on if you are happy hat you understand EVERYTHING on the page. If there is a problem (even a small one), come back on here and let m know. We can the try to sort it out.
I hope this helps,
CSG
yes, i am in fourth year at secondary.
i have SQA exams in may but first i have estimate exams in november.
i have always found chemistry difficult! i just dont understand it and its extremely hard to remeber everything for my exams :(
""Do you have a syllabus or specification that lists all the things you are supposed to know for the exams?"".....EVERYTHING i have learnt in the last 4years :( so basically everything about chemistry :S
""Do you have a textbook that goes with the course you are doing?""...we dot have textbooks, we write our OWN notes and the questions we answer are made up on the spot by our teacher as examples. i DO have Leckie standard grade chemistry books tho :) but i think i need MORE help than that :S
Thank You SOOOOO much for all your help :D im extremely greatful :D
Lisa xxxx
OK, let's get started. I don't want to try to confuse you even more by teaching you things out of sequence, so it is better to try to look at something you have already done and found difficult.
Try to tell me JUST ONE thing you cannot do at the moment. If you can't think of one for yourself, have a look at this index page
http://www.revisionworld.com/node/9039
and choose a topic to start with. It might be something you are really scared of now or it might be something that you almost understand. The choice is yours.
If you still can't think of one for yourself, try this one.
http://www.revisionworld.com/gcse/chemistry/classifying-materials/atomic-structure
It might seem like a huge task but you have made the right start by trying to do something now. Remember that the only way to eat an elephant is one bite at a time.
As soon as you can, ask your teacher to give you a copy of the syllabus (or you might call it a specification) so that you know what you have to work towards.
Have a look at this too. Which of these questions do you find easy, difficult or impossible?
http://www.sqa.org.uk/pastpapers/findpastpaper.htm?subject=Chemistry
thanx
i have looked through most of my revision notes and stuff and i am struggling a little bit with bonding....
your great help :D
lisa xx
I can't reply properly right now but will get back onto this tomorrow (Tuesday)with some ideas to help you with the bonding theories.
This might be a good place to start.
http://www.revisionworld.com/gcse/chemistry/classifying-materials/bonding/bonding-introduction
Covalent bonding:
The aim is for each of the atoms to end up with a full outer shell of electrons. For most atoms, that means eight electrons but for some very small atoms (hydrogen and helium) it only needs two elctrons.
A molecule like ammonis (NH3) has a nitrogen atom at the centre which has five electrons in its outer shell.
Deal with each hydrogen in turn. A hydrogen atom puts its one electron in for sharing. One of the nitrogen's atoms is used for sharing. Hydrogen now has a share in two electrons and so is happy. Nitrogen now has a share in six electrons. This is not a complete shell so more needs to be done.
We can bring in another hydrogen with its one electron available for sharing. The hydrogen ends up sharing two electrons and so is happy. The nitrogen now has seven electrons. Better, but still not quite there. Let's use yet another hydrogen atom (to make three altogether).
This now means that the nitrogen has a share in eight electrons (the three it has gained a share in from the hydrogens, the three it has given to be shared with hydrogen and the two it has not used for bonding). Three + three + two = eight.
See if this makes sense and then get back to me for more help....either harder examples or a simpler explanation if you need it.
eh?...
lol
sorry. i guess im just mentally challenged or just dont get things easily :(
so... it looks like a dart board basically and the outside ring has to have 8 electrons on it? yes? or am i confusing the matter? lol
thanks for doin this :D
xx
OK then. let's think about the dartboard idea for a moment. At the centre (bullseye) is the nucleus. It contains the protons and any neutrons that the atom has. The electrons are arranged around this in shells. The first shell can have a maximum of two electrons. Outside this, the second shell can have a maximum of eight electrons. Outside that one there is another shell with a maximum of eight electrons.
We often write the electron arrangement as a set of numbers. For example, if I have the element sodium (11 electrons altogether) I would need 2 in the first shell, 8 in the second shell and then the last one in the third shell. I coyuld write this as 2,8,1.
Does this make sense? Let me know and then we can move on.
i understood that!!!!
your better than my actual chemistry teacher! woo hoo!
thanks! :D:D
i would hug you if i could lol
xx
Now we will look at ionic bonding.
Think of sodium (atomic number 11 and so electrons are 2,8,1). It can have an empty outside shell by losing one electron. Since it is losing a negative charge, it becomes a one-plus ion.
Think of chlorine (atomic number 17 and so electrons are 2,8,7). It can have a full outside shell by gaining one electron. Since it is gaining a negative charge, it becomes a one-minus ion.
If you think about it, a full outside shell and an empty outside are really the same thing...it just depends on which shell you are talking about.
The sodium one-plus is attracted to the chlorine one-minus. That makes sodium chloride.
The rule is simple:
Metals lose enough electrons to give them an empty shell. The ion they make is as positive as the number of electrons they have lost.
Non-metals gain enough electrons to give them a full shell. The ion they make is as negative as the number of electrons they have gained.
The only tricky bit now is to decide how many positive ions go with how many negative ions. Simply make sure that the total of positive charges matches the total of negative charges. (eg 2 x 3+ ions can match 3 x 2- ions).
well.... that is a lil more confusing lol
i will work on ionic bonding and keep going over my notes and use this site but its still confusing :(
x
OK let's take it a bit slower.
Bonding is all about putting electrons into a more stable arrangement. It is a bit like a ball at the top of a hill being allowed to run down the hill to the bottom. The electrons in the shells in the atoms are fairly stable but a better arrangement can be found. If you have some metal atoms and some non-metal atoms, a better arrangement is often to move one or more electron(s) from the metal to the non-metal.
If the electron arrangement in the metal is 2,8,1 we can move the electron from the outsde shell to the non-metal. Losing an electron (which is negative) makes the atom into a positive ion.
When the electron joins the non-metal atom, it forms a negative ion.
The rule to decide how many electrons leave the metal atom is "REMOVE ENOUGH ELECTRONS TO LEAVE AN EMPTY OUTSIDE SHELL".
The rule for the non-metal atom is "ADD ENOUGH ELECTRONS TO GIVE A FUL OUTSIDE SHELL".
So sodium (2,8,1) loses 1.
Chlorine (2,8,7) gains 1.
The sodium 1+ ion attracts the chloride 1- ion. They form an ionic crystal lattice.
If you have a magnesium atom (2,8,2) it can lose two electrons. It forms a 2+ ion.
If you have an aluminium ion (2,8,3) it can lose three electrons. It forms a 3+ ion.
If you have an oxygen atom (2,8,6) there is room for two more electrons in the outside shell. It will gain th two electrons to form a 2- ion.
The final bit about deciding how many of each kind of ion stick together is easier to understand than it is to explain.
Once you have decided what kind of ions you have got, simply take enough positive ions and negative ions to make sure that the overall charge is zero. Here are some examples.
magnesium 2+ and chloride 1-
You need two chlorides to cancel out the magnesium.
sodium 1+ and oxide 2-
You need two sodiums to cancel out the oxide.
As always, have a look at this and let me know what you can and can't understand
still a bit confusing but i kinda understand it more ow thanks x
still a bit confusing but i kinda understand it more ow thanks x
Glad it helped. If you need more help, eithe ron this topic or on something else, just post a note on the discussion page.
i got my chemistry prelim on tuesday :S
x
I hope it goes well. If you need any help with last minute revision, come back on line.
thank you
and thanks for all ur help :)
That is why we believe in Revisionworld.
i did my chemistry general and credit chemistry exams today!!!
mg! they were soooooo difficult!
i revisied so much and my mind went completely blank in the exam! the questions were imposible!!!
:( think i failed :( lol
but thank you for helping :)
xx
This may sound silly, but whatever you did yesterday is now in the past and does not matter. What you need to concentrate on now is working hard towards your next exam. If you start now, there will be many days to study each topic. If you leave it until later, there will be less and less time.
The other thing to think about is the possibility of a resit. Does your school allow this? If it does, find out about how to re-enter and when the resit will be.
If you found some of our e-conversations useful, try another topic and see if I can help there too.
You will find it so much easier to revise if there isn't the panic of an urgent exam.
cant re-sit preliminary exams.
whats ionic?
Try this for a start. Like last time, let me know if you understand it or, if not, which bits need more explanation.
http://www.revisionworld.com/gcse/chemistry/classifying-materials/bonding/ionic-bonding
understood that! thanks :)
The idea is that the metal atom wants to lose any electrons in its outside shell. Sodium has 2,8,1 so loses the 1. Magnesium has 2,8,2 so loses the 2.
This means that sodium forms a 1+ ion and magnesium forms a 2+ ion (remember that electrons are negative so when you lose one you become more positive).
Non-metals want to gain electron(s) to fill up the outside shell. Chlorine is 2,8,7 and wants to become 2,8,8. It gains one electron and forms the chloride 1- ion. Oxygen is 2,6. It has two spacers in the outside shell and so gains two electrons to form the oxide 2- ion.
See if this makes sense and then we will stick the ions together.
i understood that as well :)
OK then,
sodium chloride needs to have one sodium ion and one chloride ion because the 1+ charge of the sodium is cancelled out by the 1- charge of the chloride. The formula is NaCl.
Magnesium chloride needs to have one magnesium ion and TWO chloride ions because the 2+ charge of the magnesium is not cancelled out by the 1- charge of one chloride ion. Two chloride ions (2 x 1-) is enough. The formula is MgCl2. (sorry I can't do the "little 2" on the website).
Magnesium oxide needs to have one magnesium ion and one oxide ion because the 2+ charge of the magnesium is cancelled out by the 2- charge of one oxide ion. The formula is MgO.
Sodium oxide needs to have TWO sodium ions and only one oxide ion because the 1+ charge of a single sodium ion is not enough to cancel out the 2- charge of the oxide ion. Two sodium ions (2 x 1+) is enough. The formula is Na2O. (sorry, again, I can't do the "little 2" on the website).
If you can do this, you have understood the bonding part of the ionic theory. If you can, great, if not, get back online and let me know. The next stage is to see what happens when millions of these ions get together to form a crystal.
understood :) thanks..
Well done, now let's build a crystal.
Imagine a sodium (+) ion next to a chloride (-) ion. If we put another sodium ion in place, the best place for it would be close to the chloride ion and as far as possible from the sodium ion. That way we would maximise the attractive forces between + and - ions but minimise the repulsion forces between the two + ions. Something like this:
Na Cl Na
The next chloride would join:
Na Cl Na Cl and so on.
Another good way to join the ions would be to have the two sodiums and two chlorides in a square with the sodium ions at opposite corners:
Na Cl
Cl Na
and we could keep that patern going since we have short distances between the opposite charge ions and a long distance (across the square) between the same charges.
Taking it even further we could have a cube with the same kind of pattern.
It would have a
Na Cl
Cl Na square on top of a
Cl Na
Na Cl square.
Again keeping the same charged ions as far apart as possible and the opposite charged ions as close as possible.
If you do the same thing with a few million million ions and you have a crystal.
i understand :)
ur a great help. thank you
x :) x
Glad it helped. Anytime you need more help on chemistry just log on and I will try to help you.
will get chemistry prelim results tomorrow so will let ya know if i passed or failed :)
i got a 4 in chemistry prelim lol
haha im so stupid and its nt advisable to take higher chemistry :( ohwel lol
x
Don't be too disappointed. Chemistry is a difficult subject. If you continue to study, remember that you can always log-on here for some help.