Why did mendeleev put bromine (br) and chlorine (cl) in the same group on the periodic table?

They have similar properties.Bromine and Chlorine both have equal chemical properties. They both have 7.electrons in the outermost energy level. They both gain 1 electron to get the. noble gas configuration.Cl and Br have same chemical properties. They have 7,valence electrons. They both are non-metals. Bromine and chlorine are in group VII A, which could also be designated Group 7a, of the narrow form periodic table that was commonly used before 1980. Most chemists now prefer a wide form periodic table, in which these elements are in column 17. The periodic table has been set up to illustrate the repeating nature of the elements as we progress along their atomic number. Cl (chlorine) and Br (bromine) are very similar because they both have seven valence electrons, and both need only one more to be like a noble gas. (The need to have eightelectrons in the outer main shell is called the octet rule, and the reason for this is understood by scientists, but is complicated.) HOPE IT HELPED