going down the periodic table, the size increases (thius should be obvious. you have more protons and neutrons, hence a bigger neuclues, and more electrons around it)
Going from left to right, the size decreases. Why? because as you go across from left to right, you have more protons in the nucleus. This in turn pulls the electrons tighter to the nucleus (since protons are positively charged, and nuclei are negatively charged)
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