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.
(12) Now David was the son of an Ephrathite of Bethlehem-Judah, whose name was Jesse who was .... (years) old at the time of Saul. (13) And the 3 eldest sons of Jesse had marched with Saul to the war, (14) and David was the youngest, (15) and David had remained to feed his father's sheep at Bethlehem.