Tuesday, 12 June 2012

Ionic Compounds

Note: Updated as of 2/1/13, and this blog is no longer being updated because I'm done with IGCSEs and am doing IB, which is seriously hectic. I apologise that this blog is not totally complete but it's all I have and I'm sorry. 

f) Ionic compounds

1.27 describe the formation of ions by the gain or loss of electrons

Ions are atoms or molecules with an electric charge due to the gain or loss of electrons. If electrons are lost, the ion has a positive charge. Metals tend to do this, so they form cations (positive ions), so normally elements from group 1-3 will form cations.

If electrons are gained, the ion has a negative charge. Non-metals tend to do this, and they form anions (A-Negative-ION - ANION). So elements from group 5-7 will form anions. Group 0/8 are the noble gases and are inert + unreactive, so they do not form ions.

1.28 understand oxidation as the loss of electrons and reduction as the gain of electrons

OILRIG -  Oxidation Is Lost, Reduction Is Gain

1.29 recall the charges of common ions in this specification


Positive ions/Cations
Negative ions/Anions
Charge
Name of ion
Formula
Charge
Name of ion
Formula
1+
Ammonium
Copper (I)
Hydrogen
Lithium
Potassium
Silver
Sodium
NH4+
Cu+
H+
Li+
K+
Ag+
Na+
1-
Bromide
Chloride
Hydroxide
Fluoride
Iodide
Nitrate
Hydrogencarbonate
Br-
Cl-
OH-
F-
I-
NO3-
HCO3-
2+
Barium
Calcium
Copper (II)
Iron (II)
Lead (II)
Magnesium
Nickel (II)
Strontium
Zinc
Ba2+
Ca2+
Cu2+
Fe2+
Pb2+
Mg2+
Ni2+
Sr2+
Zn2+
2-
Carbonate
Sulphate
Sulphite
Sulphide
Oxide
CO32-
SO42-
SO32-
S2-
O2-
3+
Aluminium
Iron (III)
Al3+
Fe3+
3-
Nitride
Phosphate
N3-
PO43-


1.30 deduce the charge of an ion from the electronic configuration of the atom from which the ion is formed

So if the electronic configuration is 2.8.1, you can see that the atom has one outer shell electron only. And so it only needs to lost that to have a full outer shell. So its ion would have a positive 1 (1+) charge, as the electronic configuration would be 2.8. Basically, if there are less outer shell electrons to lose to have a full outer shell, then the charge will be positive. (Here, it is easier to lose than gain, because the ion would have to gain SEVEN electrons to have a full outer shell!)

Another example, if the electronic configuration is 2.8.7, then the atom only needs to gain 1 outer shell electron to have a full outer shell. So the ion formed would have the electronic configuration of 2.8.8, and so the charge would be negative 1 (you’re gaining one electron, which has a negative charge (1-) ). Thus if it is easier to gain electrons, (it is here, rather than losing 7 outer shell electrons), then the charge will be negative.




Here, the Sodium (Na) has lost one electron. It doesn't have equal numbers of protons and electrons anymore; it has one less electron than protons (or you can think of it as one more proton than electrons), so it has a 1+ charge. 

The chlorine, on the other hand, has gained one electron. So it has one more electron than proton, thus it has a negative 1 charge (1-). The formula for sodium chloride is NaCl. 



The magnesium atom loses 2 electrons to an oxygen atom, and they both have full outer shells now. It is common that ions form noble gas structures like this to become more stable and unreactive like the group 0/8 elements. 

The magnesium oxide is held together by very strong attractions between the ions. The ionic bonding is stronger here than in sodium chloride as this time you have 2+ ions attracting 2- ions. The greater the charge, the greater the attraction.

The formula for magnesium oxide is MgO.


1.31 explain, using dot and cross diagrams, the formation of ionic compounds by electron transfer, limited to combinations of elements from Groups 1, 2, 3 and 5, 6, 7




This is a common example, it doesn't matter which element has dots/crosses for their electrons,  the important thing is to make it clear that the electrons are transferred from one atom to another to make 2 ions. The one losing an electron here is sodium, so it becomes a positive ion called a cation, and the chlorine atom gains an electron and becomes a chloride ion (an anion).

Diagram of bonding in magnesium oxide. A magnesium ion (2,8)2+ gives two electrons to an oxide ion (2,8)2-. Both ions have full highest energy levels
Magnesium oxide: MgO
Even though only one magnesium ion and one oxide ion is shown, the actual equation is:
2Mg + Oà 2MgO
(remember that oxygen is diatomic)

Diagram of bonding in calcium chloride. A calcium ion (2,8,8)2+ gives one electron to a chloride ion (2,8,8)- and another electron to another chloride ion (2,8,8)-. All three ions have full highest energy levels
Calcium chloride: CaCl2
However, here you have to show 2 chloride ions because calcium loses 2 electrons, and 2 chlorine atoms gain an electron each to form 2 chloride ions.

1.32 understand ionic bonding as a strong electrostatic attraction between oppositely charged ions
^self-explanatory

1.33 understand that ionic compounds have high melting and boiling points because of strong electrostatic forces between oppositely charged ions
The strong electrostatic forces between oppositely charged ions are ionic bonds as mentioned in the previous spec point. And these require a lot of energy to break, hence high melting/boiling points. 

19 comments:

  1. SHIT Blog!! Didn't even cover all the Ionic Compounds syllabus! Didn't help at all. Don't know why do you even bothered posting such shit information out on the internet.

    For other viewer, this blog is missing a lot of information that is needed to be covered. The person who wrote this shit ass blog probably got a C in examination!

    ReplyDelete
    Replies
    1. Please don't reproduce, it would be a favour to the human race if your genes were not carried on.

      Thanks you very much

      Delete
    2. I agree to the 1st comment, this blog is indeed missing some bits. Can you please update this blog?

      Delete
    3. I've just updated this post and I've put up notices on this blog explaining that I've finished IGCSEs and am doing IB, so I don't really have time to update the blog. I'm really sorry about that, this is all that I had time for back then and it took me a lot of time since I did 4 blogs. This will be the last update though, since this post was incomplete..

      And as for the first comment: you can think what you like but I actually got an A* and did Single Science. I'm sorry you don't find this useful but the reason I did the blog was partly to revise myself, and I did fine. :)

      Delete
  2. Hi, I find this IGCSE blog very useful, and I'm starting IB next year, so is it alright if you could tell us the URL to your IB blog please?

    ReplyDelete
    Replies
    1. Hey I'm doing IB myself and I don't actually have any IB blogs, too much to handle! Sorry!!

      Delete
  3. Michelle, thank you this is great :)
    I really appreciate the effort and time you put into this.
    I am doing my IGCSEs this year, as science is very important to me I really appreciate your help (I am hoping to study medicine in the future).

    Good luck with your IB! I'm also going to start the program next year. Interested to know what subjects you took?

    You lovely little human being, thanks and good luck ^^

    ReplyDelete
    Replies
    1. Hi there thank you so much for your kind comment, I'm glad you appreciate this blog!! :)

      And thanks!!, good luck with your IGCSEs too! Really hope the blogs helped. And actually, science-wise I'm doing HL Bio and Chem, subjects you're probably thinking of doing since you're interested in medicine!

      If you have any questions feel free to ask / email me. :)

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  4. what is the reason that compounds are not formed by the loss or gain of protons?

    ReplyDelete
    Replies
    1. Well generally atoms don't lose or gain protons because they are tightly bound along with neutrons in the nucleus - it's because of the 'strong nuclear force'. The exception being in radioactive decay.. and when they do lose/gain protons..they'd be a different element since the proton number is unique to each element.

      So atoms normally lose/gain electrons to become ions and form ionic compounds. :) (The electrons are in orbitals around the nucleus and aren't as tightly bound so they can be lost)

      Delete
  5. Hi everyone, I've also typed my notes up in a similar blog... (all credit for the idea goes to Michelle of course).

    http://askcaitlinchemistry.blogspot.com

    ReplyDelete
    Replies
    1. do you have it for the whole cyllabus??

      Delete
  6. Dear GCSE Girl, I have just checked out your blog, and I am a bit disappointed. You have basically just copied Michelle's blog. You have the same layout, homepage...I mean, you could have arranged everything in like a contents page at least (because Michelle didn't do it). Just because you have a different format, doesn't mean that it's your work. And, it's stupid how you say "in a similar blog" because IT IS THE SAME, and that you're sating "all credit for the IDEA goes to Michelle." Don't you mean BLOG, not IDEA!!

    ReplyDelete
    Replies
    1. Thank you anonymous for this comment. :)

      Delete
  7. AMAZING BLOG EXPLAINED IT BTR THAN MY TEACHER! GOOD LUCKK MY SISTER IS ALSO DOING IB BIO AND CHEM HL XX

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  8. Michelle, I really need to say a HUGE THANK YOU to you for all of these notes! My science teachers are about as inspiring as rocks, and your blogs have really helped me throughout the parts of the GCSE course that I have done so far! my mocks are soon, and I really appreciate the amount of hard work, time and effort that has been put into these blogs for the benefit of other. Thanks one again, and good luck with IB!! xx

    ReplyDelete
    Replies
    1. You're very welcome!! Good luck for your mocks and hope you do well!! :) :)

      Delete
  9. YOU HAVE SAVED MY LIFE AND MY ACADEMIC STATUS THANK YOU!!!

    ReplyDelete
  10. Thanks Michelle for the information.

    ReplyDelete

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Note: This blog will no longer be updated as I finished IGCSEs in 2012. Sorry! :( If you are interested in buying IB notes though, please contact me. :)