Strontium and barium form ionic compounds because of their

Be+2 < Mg+2 < Ca+2 < Sr+2 < Ba+2 Size of ions As the size of cation increases polarising power of cation decreasesDistortion of electron cloud in anion decreases hence sharing property of electron pair in M-Cl bond decreases means transfer of electron property increases Ionic nature of bond increasesSo, Barium compounds are ionic in nature