1- I have an exam tomorrow and there are a few question I need to understand, I

Question

1- I have an exam tomorrow and there are a few question I need to understand, I know what the right answer but I need explanition please..

in which of the following atoms is the 3s orbital closest to the nucleus?

1) Se 2)Br 3) As 4) Ga 5) Ge

2- of the elements below, which would have the least negative electron affinity?

1)Si 2)P 3)S 4)Cl 5)F

(for the question above, if its asked for the most positive, what should the answer be )

3- for molecules with only one central atom, how many lone pairs on the central atom gurantee molecular polarity?

1) 1 2) 2 3) 1 or 2 4) 3 5) 1 or 3

Explanation / Answer

1. All these are from period 3, So, as the atomic number increases across a period, atomic radius decreses due to greater effective nuclear charge, This means that as atomic number is increased, the potential of increased nuclear density(due to increase in proton only) can more effectively attract the electrons.So, greater atomic number means greater nuclear charge, means more strength to attract electrons, hence electrons are more closer in this case.

So, highest atomic number is for Br (35) [ Ga-31,Ge-32, As-33, Se-34, Br-35] which means it has the closest 3s orbital.

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