There are three stable allotropes of oxygen: dioxygen (O2), ozone (O3) and nonaoxygen (O4). Here are some physical differences between dioxygen and ozone, the two main allotropes:

- Molecular weight: O2 has a molecular weight of 32 g/mol, while ozone has a molecular weight of 48 g/mol.

- Bond length: The bond length in O2 is 121 pm (picometers), while the bond length in O3 is 127 pm.

- Bond angle: The bond angle in O2 is 180 degrees, while the bond angle in O3 is 116.8 degrees.

- Magnetic properties: O2 is paramagnetic, meaning it is weakly attracted to a magnet, while ozone is diamagnetic, meaning it is not attracted to a magnet.

- Melting point: O2 has a melting point of -218.4 degrees Celsius, while ozone has a melting point of -193 degrees Celsius.

- Boiling point: O2 has a boiling point of -183 degrees Celsius, while ozone has a boiling point of -111.9 degrees Celsius.

- Density: O2 has a density of 1.429 g/L at 0 degrees Celsius and 1 atmosphere, while ozone has a density of 2.144 g/L at 0 degrees Celsius and 1 atmosphere.

- Appearance: O2 is a colourless gas, while ozone is a pale blue gas.