Looking across period 4 of the periodic table, potassium (atomic number 19) is followed by calcium (atomic number 20), which is followed by scandium (atomic number 21). Which element should have the largest atomic radius?
1.potassium
2.calcium
3.scandium
4.All three have the same atomic radius

Question

Looking across period 4 of the periodic table, potassium (atomic number 19) is followed by calcium (atomic number 20), which is followed by scandium (atomic number 21). Which element should have the largest atomic radius?
1.potassium 
2.calcium
3.scandium
4.All three have the same atomic radius

parthkohli · Answer

$$r_n = \dfrac{n^2}{\rm Z} 0.529 \overset{\circ}{\rm A}$$The atomic radius is at $n = \rm outermost~shell$.