Atomic radius

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Katherine Grillo 1B
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Joined: Fri Sep 28, 2018 12:28 am

Atomic radius

Postby Katherine Grillo 1B » Fri Nov 09, 2018 12:00 am

Why does the atomic radius decrease across a period and increase down a group? I'm confused about the relationship between electrons/shells and size.

Posts: 69
Joined: Fri Sep 28, 2018 12:23 am

Re: Atomic radius

Postby Andre_Galenchik_2L » Fri Nov 09, 2018 12:11 am

The atomic radius increases down a group as another shell of electrons is being added (energy level). Once the second period hits 8 electrons, its shell becomes full and a new shell (the n=3 shell) begins. Across a period the radius decreases because as the shell remains the same, the number of protons increases, pulling in the electrons.

Sean Reyes 1J
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Joined: Fri Sep 28, 2018 12:24 am

Re: Atomic radius

Postby Sean Reyes 1J » Sat Nov 10, 2018 4:31 pm

Atomic radius decreases across a period because of the pull that the protons have on the outermost shell. Across a period, the amount of core electrons doesn't increase, which means there is a higher effective nuclear force across a period. This results in a stronger pull on the electron cloud, effectively making the atomic radius smaller.
Atomic radius increases down a group because the principal quantum number is increasing. This correlates to shells, which implies that with more shells, there will be a greater atomic radius.

MaanasO 1A
Posts: 72
Joined: Fri Sep 28, 2018 12:26 am

Re: Atomic radius

Postby MaanasO 1A » Sat Nov 10, 2018 4:57 pm

As you go the right across a period, more protons are added to the nucleus => the nucleus has a greater positive charge => it has a tighter pull on the electrons. Down a group however, because the quantum number n increases, the electrons are significantly further away, which causes the atomic radius to increase.

Hope that helps!

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