Question about Lewis Structures... help

[americanpierg]

Say you're given a covalently bonded compound containing a transition metal. How do you know how many total electrons there are?

MnO2... how would you draw the lewis structure for that?

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[navneetdh]

I think you will have to figure out the electronic configuration of Mn to find the valence electrons it has
Mn = [Ar] 3d7 4s2

so valence electrons are 2

now adding oxygen valence you have 2+6 = 8

so total 8 valence electrons

But I am now confused how would you draw that structure????

 

[americanpierg]

I think you will have to figure out the electronic configuration of Mn to find the valence electrons it has
Mn = [Ar] 3d7 4s2

so valence electrons are 2

now adding oxygen valence you have 2+6 = 8

so total 8 valence electrons

But I am now confused how would you draw that structure????

actually i figured it out. And BTW, Mn is actually [Ar] 3d5 4s2. total valence electrons is 7, which is bascially all the lectrons left over after [Ar], or outermost s and 2nd to outermost d if its a transition metal. (or you can just look at which number column its on, in this case 7)

oxygen has 12 valence electrons, and manganese has 7, so total is 19.

Mn is in the middle, double bonded to each oxygen atoms (leaves all 3 with 0 formal charges). 2 lone pairs on each oxygen, and 3 electrons on Mn.

interesting thing is also that a complete d orbital is more favorable than a complete s orbital, so elements in the Co, Cu families have 4s1 as the electrons in d pairs up first. Cr family is 1 d orbital away from filling up all 5, so its also left with 1 electron in the 4th s orbital.

 

[navneetdh]

oh i get that there are 2 oxygens so yeah 12 valence for oxygens.

but how is Mn 7? aren't valence electrons the ones only in the last orbital and since it is 4th here which only has s there are 2.

right???

 

[americanpierg]

oh i get that there are 2 oxygens so yeah 12 valence for oxygens.

but how is Mn 7? aren't valence electrons the ones only in the last orbital and since it is 4th here which only has s there are 2.

right???

valence electrons are those on the outermost shell OR those available for bonding.

for non transition metals, its outermost s and p orbitals. for transition metals, its outermost s and 2nd to outermost d. for lanthanide and actinide, its s of outermost, d of 2nd to outermost, and f of 3rd to outermost.