What are the groups on the periodic table let us predict how elements will react

The vertical columns are called groups.

Explanation:

Periodic table consist of vertical columns and horizontal rows.

Vertical columns are called groups while horizontal rows are called periods.

There are seven periods and 18 groups in periodic table.

The elements in same group have similar properties and can react in a similar way.

The elements in same group have same number of valance electrons that's why their reactivity is same.

Consider the example of alkaline earth metals. They are present in group two and have same number of valance electrons (two valance electrons).

They react with oxygen and form oxide.

2Ba + O₂ → 2BaO

2Mg + O₂ → 2MgO

2Ca + O₂ → 2CaO

this oxide form hydroxide when react with water,

BaO + H₂O → Ba (OH) ₂

MgO + H₂O → Mg (OH) ₂

CaO + H₂O → Ca (OH) ₂

With sulfur,

Mg + S → MgS

Ca + S → CaS

Ba + S → BaS