Answer:
On the periodic table, the halogens are the last but one group (vertical column), right next to the noble gases. The group number is 7 which indicates that halogen atoms contain seven electrons in the outer shell (energy level).
Their chemical formulae are F 2, Cl 2, Br 2 and I 2. The bond between the atoms in a molecule is very strong, but the forces of attraction between molecules are weak. This explains why group 7 elements have low boiling points. ... Astatine is placed below iodine in group 7.