Trend in atomic radius of Period 3 elements

What is here?

Atomic radius decreases going across Period 3.   You can:

• view a table of atomic radii
• view a graph of atomic radii
• learn why atomic radius decreases going acrosss Period 3

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Table of physical data

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Graph of physical data

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Explanation of this trend

Going across Period 3:

• the number of protons in the nucleus increases so ...
• the nuclear charge increases ...
• there are more electrons, but the increase in shielding is negligible because each extra electron enters the same principal energy level ...
• therefore the  force of attraction between the nucleus and the electrons increases ...
• so the atomic radius decreases.

As the number of electrons in each atom increases going across Period 3, you might expect the atomic radius to increase. This does not happen,  because the number of protons also increases and  there is relatively little extra  shielding from electrons in  the same principal energy level.

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