How is the total number of electrons represented in a Lewis structure determined?

Answer 1

How else but by counting up (i) the number of valence electrons on the neutral atoms, and (ii) the charge on the atom or ion............?

We now construct Lewis structures by expanding from neutral atoms, and the charge on the atom or radical ion must obviously be taken into consideration.

Take for example #"nitrate ion"#, #NO_3^(-)#. Nitrogen, Group V, has 5 valence electrons; oxygen, Group VI, has 6 valence electrons. And we throw in another electron, so that we have #5+3xx6+1=24# #"valence electrons"#, i.e. #"12 electron pairs"# in the Lewis structure of #NO_3^-# to distribute around 4 centres.
And thus we get #O=N^+(-O^-)_2#. From the left, around the doubly bound oxygen there are #2+2# lone pair electrons on oxygen, (i) #4# electrons, and in the #O=N# bond, (ii) #4# electrons, NO lone pairs on the cationic, quaternized nitrogen, and (iii) #2xx8=16# electrons on the formally singly bound oxygens, each of which bears a NEGATIVE charge: thus 24 valence electrons as required for the Lewis structure.

Therefore, all we have to do is take the number of valence electrons (which is determined by the Group number of the atom), add these numbers together, and then adjust the result based on whether the species is positively or negatively charged.

Can you do the same for #PO_4^(-3)#? There must be 32 electrons to distribute, i.e. 16 electron pairs.
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Answer 2

The total number of electrons in a Lewis structure is determined by summing the number of valence electrons from all the atoms involved in the molecule or ion.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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