## lecture question 5/2

tatianatumbling_1J
Posts: 31
Joined: Mon Jan 08, 2018 8:19 am

### lecture question 5/2

can someone explain the concept the professor went over. he talked about why radii get smaller and I know it has to do with attraction to the nucleus. I think it was called shell contraction? (Sorry this is so vague)

Anna De Schutter - 1A
Posts: 66
Joined: Wed Feb 21, 2018 3:01 am

### Re: lecture question 5/2

Hi!

I'm not too sure if it was called shell attraction, but how I understood it is that across a period, the atomic radius decreases. This is because across a period, we still remain in the same shell (n=1 for example, or n=2, etc.), yet the number of protons increases. Thus, the electrons are more attracted to the nucleus when we go across a period (because of more protons) and as a result, the atomic radius decreases.

Down a group, however, the atomic radius will increase because the number of shells increases.

I hope this helps! :)
Anna De Schutter - section 1A

tatianatumbling_1J
Posts: 31
Joined: Mon Jan 08, 2018 8:19 am

### Re: lecture question 5/2

Anna De Schutter - 1A wrote:Hi!

I'm not too sure if it was called shell attraction, but how I understood it is that across a period, the atomic radius decreases. This is because across a period, we still remain in the same shell (n=1 for example, or n=2, etc.), yet the number of protons increases. Thus, the electrons are more attracted to the nucleus when we go across a period (because of more protons) and as a result, the atomic radius decreases.

Down a group, however, the atomic radius will increase because the number of shells increases.

I hope this helps! :)
Anna De Schutter - section 1A

thank you!

Garrett Dahn 1I
Posts: 28
Joined: Fri Apr 06, 2018 11:02 am
Been upvoted: 1 time

### Re: lecture question 5/2

I'd like to reference the final part of your question about contraction. Professor Lavelle called this electron contraction because the electrons are literally being contracted by the increasing positive charge of the nucleus, since as you move to the right on the periodic table, the number of protons (positively charged) increases and the nucleus pulls harder on the electrons. So as you move to the right on the periodic table, electron contraction decreases the atomic radii, so the smallest atoms (in terms of radius) are those with the fewest shells and the most protons (i.e. those elements which inhabit the upper-right hand corner of the Periodic Table).