## Chemistry: The Central Science (13th Edition)

The order of the atoms in increasing size: $$Cl\lt S\lt K$$
In the periodic table: - As we move from left to right across a row, atomic radii tend to decrease (due to the constant increase of the nuclear charge) - As we move from top to bottom across a column, atomic radii tend to increase (due to the availability of new orbitals with higher principal quantum number $n$ which are further from the nucleus) S and Cl are in the same 2nd row. From left to right, S appears first, then comes Cl. According to the trend above, the atomic radium of S is larger than that of Cl. In other words, $S\gt Cl$. K is in the 3rd row. Being in the 3rd row means the addition of new orbitals further than the nucleus than being in the 2nd row. That means there is more chance to find electrons further from the nucleus in K than in S and Cl. The radium of K, as a result, is larger than both S and Cl. Overall, the order of the atoms in increasing size: $$Cl\lt S\lt K$$