polyatomic ions

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Daniela Alvarado 3B
Posts: 34
Joined: Fri Sep 28, 2018 12:26 am

polyatomic ions

Postby Daniela Alvarado 3B » Sat Nov 10, 2018 5:59 pm

how exactly do we draw these? do we add/ subtract valence electrons (based on the charge given in the chemical formula), and just add a bracket and charge? or is there something else we must do?

Sarah Jeong 4F
Posts: 30
Joined: Fri Sep 28, 2018 12:27 am

Re: polyatomic ions

Postby Sarah Jeong 4F » Sat Nov 10, 2018 6:16 pm

Yes, it is basically the same process as a polyatomic lewis structure, except you add/subtract valence electrons(based on the charge given in the chemical formula) on the actual lewis structure. Also bracket it and put the charge on the outside.
So for example, on the attached picture, it would regularly have 24 ve, but if you count in the picture, there are 26ve, because of the added (2-) electrons.
polyatomic ions.jpg

Joaquin Andrade
Posts: 31
Joined: Fri Sep 28, 2018 12:27 am

Re: polyatomic ions

Postby Joaquin Andrade » Sat Nov 10, 2018 6:33 pm

To draw the lewis structures of polyatomic ions we first add up the total valence electrons. For instance, take sulfate SO4 -2. Both sulfur and oygen have 6 valence electrons - there are 4 oxygens so the total number of electrons is 30. But since the charge is -2 we add 2 electrons for a total of 32. Sulfur is the central atom since it has a lower ionization energy. We first write down single bonds between the sulfur and oxygen, making a total of four. Then we go around completing the octets for the oxygens making sure we use 32 electrons. At this point we have a -1 formal charge for each oxygen and a +2 formal charge for the sulfur for a total charge of -2. But we want to minimize formal charge, so we form double bonds. We can form two double bonds between the sulfur and two oxygens to remain once again with a -2 charge. Then we add brackets and and the respective charge, and we’re done.

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