[peterpan1372]

Hello,

Could someone help me out?
I thought of a because MgCl2 is balanced out and there are 3 of argon which would imblance it ...

[Arkcon]

Hello,

Could someone help me out?
I thought of a because MgCl2 is balanced out and there are 3 of argon which would imblance it ...

No.  Because that's not what the question is asking.  Kindly draw the electronic structure of each pair, and see which ones don't match.

http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/fundamentals/atomsrev4.shtml

You will need to have this concept down correctly and be able to intuit it quickly on a standardized test, because you can't be drawing each under a time limit.

[peterpan1372]

You can work out the electronic structure of an atom from its atomic number or its position in the periodic table. Start at hydrogen, H, and count the elements needed to reach the element you are interested in. For sodium, it takes:
•2 elements to reach the end of the first period (row)
•8 elements to reach the end of the second period
•1 element to reach sodium in the third period.
The diagram of the periodic table shows how this works.


my question: what do they mean by the first subpoint and the third subpoint?

[peterpan1372]

or could someone explain it for me in a sample?

For example: why do CO and N2 have the same electronic structure?

[Corribus]

In this context "electronic structure" typically refers only to how electrons are organized in molecular bonds between the nuclei. N₂ and CO have the same electronic structure in the sense that they have the same occupied and unoccupied molecular orbitals. I.e., they both have a triple bond composed of a sigma bond and two mutually perpendicular pi bonds.

[peterpan1372]

I don't understand that really. Sigma is a single bond and pi is a double bond... where are they located for example?

[Corribus]

N≡N

C≡O

Nitrogen has 5 valence electrons, so N₂ has a total of 10 valence electrons available for bonding. Carbon has 4 valence electrons and Oxygen has 6 valence electrons, therefore combined there are 10 valence electrons available for bonding.

You should google "MO diagrams" of nitrogen and carbon monoxide and you will see how the ordering of the molecular orbitals and bonds is therefore similar for the two molecules.