The halogens are a group of elements found in Group 7 of the periodic table. They include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Each of these elements has unique physical properties that change as you go down the group.

1. States of Matter:

• Fluorine (F): This is a pale yellow gas at room temperature. It’s super cold at about -188 °C.
• Chlorine (Cl): This element is a greenish-yellow gas at room temperature. Its temperature is about -34 °C.
• Bromine (Br): Bromine is a reddish-brown liquid that melts at -7.2 °C.
• Iodine (I): Iodine is a bluish-black solid that melts at 113.7 °C.
• Astatine (At): Astatine is rare and radioactive. Its properties aren’t very well-known because it breaks down quickly.

2. Physical Appearance:

• The colors of these elements change from pale yellow (fluorine) to black (iodine).
• Bromine is special because it's the only liquid non-metal at room temperature.

3. Density Trends:

• The density, or how heavy these substances are, increases as you go down the group:
  • Fluorine: 1.696 g/L (gas)
  • Chlorine: 3.214 g/L (gas)
  • Bromine: 3.12 g/cm³ (liquid)
  • Iodine: 4.93 g/cm³ (solid)

4. Boiling and Melting Points:

• The boiling and melting points increase as you go down the group because the size of the molecules gets bigger and the forces holding them together become stronger:
  • Fluorine: -188 °C (boiling point)
  • Iodine: 184 °C (boiling point)

Knowing these properties helps us understand how the halogens react and how their characteristics change.