atomic size quiestion (li and k)

:roll: i have a problem. i know that the radius are affected by the number of protons. More protons , less radius.however, K's radius size is bigger than li's.IN fact, K has more protons than li.please help me


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more electrons

I believe, it is as my old teacher told me: There is more "stuff" :D .
Potasium has more electrons because it has more energy levels therefore its radius is larger than lithium which has only 3 electrons. K has 19 electrons so it has 2 s orbitals and 2 p orbitals completely filled. If you still don't understand what i mean look at lithium and Potassium on this site and look at the model on the right side of the screen.

reply cant find the figure

As the title , i cant find figure to solve my problem. actually i am a beginner of chemistry and i've just entered this web site yesterday. would you like to spend little time to tell me where it is.thanks !

Go to
You can find a lot of information there. On the bottom of these pages you can see a graph. As you can see on it : if you go down the group atomic radius grows up. If you go through the period, atomic radius gets smaller (it`s the rule). Because of it Cs has the biggest radius- 298 pm, and He has the smallest one- 31pm.

WebElements: the periodic table on the WWW []

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