Types of Bonds can be predicted by calculating the difference in electronegativity.
If, Electronegativity difference is,
Less than 0.4 then it is Non Polar Covalent
Between 0.4 and 1.7 then it is Polar Covalent
Greater than 1.7 then it is Ionic
For Ca and K,
E.N of Calcium = 1.00
E.N of Potassium = 0.82
________
E.N Difference 0.18 (Non Polar Covalent)
For Ca and Mg,
E.N of Magnesium = 1.31
E.N of Calcium = 1.00
________
E.N Difference 0.31 (Non Polar Covalent)
For Ca and Br,
E.N of Bromine = 2.96
E.N of Calcium = 1.00
________
E.N Difference 1.96 (Ionic)
For Ca and S,
E.N of Sulfur = 2.58
E.N of Calcium = 1.00
________
E.N Difference 1.58 (Polar Covalent)
Result:
The bond between Calcium and Bromine is Ionic in Nature.