The shielding of electrons gives rise to an effective nuclear charge, zeff, which explains why boron is larger than oxygen. estimate the approximate zeff felt by a valence electron of boron and oxygen, respectively?

The solution would be like this for this specific problem:

 (atomic number) - (core electrons) 

Boron:

Atomic number: 5 
Core electrons: 2

Boron will have the following: 2 core electrons and 3 valence electrons.
(atomic number) - (core electrons)> (5) - (2) = +3 

Oxygen: 
Atomic number: 8 
Core electrons: 2 

Boron will have the following: 2 core electrons and 6 valence electrons. 
(atomic number) - (core electrons)> (8) - (2) = +6 |

So the answer would be +3 and +6.

I hope this helps and if you have any further questions, please don’t hesitate to ask again. 

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