Because attraction of water molecules around an ion depends on. that ion's density of charge, smaller ions (and thus ions of greater ionic. potenti. al) attract more water molecules. The result is the. inverse. relationship. between non-hydrated radius and hydrated radius shown below.
[v. 5] In Hebron he reigned over Judah seven years and six months: and in Jerusalem he reigned thirty and three years over all Israel and Judah.   This would have made David 37 when he became king of all Israel. Do not get confused between 'Judah' and 'Israel': they are not the same.
In 1 Kings 2:10, 11 we find how long he reigned over Israel: So David slept with his fathers, and was buried in the city of David. And the days that David reigned over Israel were forty years: seven years reigned he in Hebron, and thirty and three years reigned he in Jerusalem.