Answer:
One difference between Group 7 of the modern periodic table and Group 7 in Mendeleev's periodic table is the placement of the elements.
In Mendeleev's periodic table, Group 7 consisted of manganese (Mn), technetium (Tc), and rhenium (Re). In the modern periodic table, Group 7 consists of the halogens: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).
The halogens are a group of highly reactive nonmetals, while the elements in Group 7 of Mendeleev's periodic table were not all nonmetals and did not share the same chemical properties as the halogens.
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