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Thread: Dot cross diagrams

  1. #1 Dot cross diagrams 
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    hi,

    I am trying to revise for my chemistry AS exam and I am really stuck on dot cross diagrams, we only have to do simple ones e.g SO2

    any help will be greatly appreciated!


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  3. #2  
    Forum Freshman Samuel P's Avatar
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    Hi there Katie, I'm doing Chemistry A2, so it's been a while since I did dot cross diagrams, but what exactly are you in need of?

    Is it the concept as a whole? I'll have a quick look through my AS book and see if I can put what's in there into layman's terms.

    As far I can see, you only have to learn ionic and covalent bonding,

    a covalent bond is formed by the sharing of electrons between one or more atoms to form a compound.

    an ionic bond involves a metal and none metal. Intermolecular forces between oppositely charged ions. I understand that's a hard concept to grasp for most, so the way you can imagine it is that the two oppositely charged poles of a magnet sticking together as they have formed intermolecular bonds as a result of their opposite charges.

    So from this you can see that in covalent bonds, the circles in the diagrams overlap and in ionic bonds they simply donate electrons and are then held together by the forces inbetween them.

    It would perhaps be easier if you were to ask specific questions and I'll try and get back to you as fast as I can because I know you need the help pretty quickly ^_^.

    Also, make sure you understand shells of atoms also as the understanding of that makes it much easier to understand this.

    I got mint in my eye while writing this so it distracted me a little and it might be a bit rubbish.. it burns!!

    Anyway, if you respond I'll be more than happy to help you out.


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  4. #3 .. 
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    heeeey

    thats great thanks i understand the concept of ionic, metallic and covalent bonding, I also understand electron shells, I just get very confused on how to draw it! any help on drawing it would be great!

    yepp definatley need answers fast, exams on thursday if the snow doesnt cancel it! haha

    hope you have got the mint out of your eye......
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  5. #4  
    Forum Freshman Samuel P's Avatar
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    I missed my last Chemistry exam, illness urgh, so I have one on Thursday too! ^_^

    They can't be cancelled, people say that, but they take months to schedule, so if you're not in on the day of your exam, you miss the exam and fail.

    My eye's alright now :P I don't even know how it happened.

    Ok, so obviously different types of bonding result in different dot-cross diagrams.
    I'll draw them out on paint... :P

    Covalent Bonding:

    A shared pair of electrons is called a single covalent bond, and each atom contributes
    one electron to the bond.

    One type of atom (element) will have a dot to represent its electron(s) and one will have a cross.

    In covalent bonding, as you know, the electrons are shared, which results in a dot cross diagram looking like this:



    Now, let's apply that to a certain elements. Each atom wants to fill its outer shell of electrons depending on which shell is its outer shell. E.g. hydrogen only wants one electron because it only needs two in total to fill its outer shell. Oxygen wants to have eight electrons in its outer shell, because of the amount of electrons it has, its outer shell is full with eight. (As I'm sure you know from shells, that's why I'm making it so basic).

    A single bond is when each atom donates one electron to share to another atom (or numerous atoms, as long as it is only sharing one with each, forming one electron pair).

    E.g.



    Now of course, the more electrons that are donated by the elements to each other, the more electron pairs that are formed in the atoms outer shells, the more bonds that are considered to be formed between them. 1 electron = single, 2 = double, 3 = triple. Which of course works with elements like nitrogen.



    Ionic Bonding

    Ionic bonding is a concept that you said that you understand, so you'll have no trouble understanding how to draw a dot cross diagram. It simply works by the donation of electrons from one atom to another, making one positively charged and one negatively charged. This opposition in charges holds them together by electrostatic attraction. The metal ion will be positive and the non-metal ion will be negative ^_^.

    I said before that it was intermolecular forces, that was wrong, sorry! It's electrostatic as I've just stated.

    Anyway...

    As you can imagine, the presence of all these oppositely charges ions leads to a big structure as they're all surrounded by atoms they're attracted to, holding them all together. This is how a giant ionic lattice is formed.



    Ionic lattice due to oppositely charged ions.


    Sometimes you'll need more of one element to accept or donate all the electrons required.

    Here's an example:



    I hope I helped, because it took me a very long time! ^_^
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