Br2 molecules contain pure covalent bonds between the bromine atoms and are held together by London dispersion forces between the molecules.
Bromine (Br), a halogen element, exists naturally as a diatomic molecule, meaning two bromine atoms are chemically bonded together to form Br2. Understanding how these atoms bond within the molecule and how the molecules interact with each other is key to understanding the properties of bromine, such as why it's a liquid at room temperature.
The Bonding Within the Br2 Molecule
Inside a single Br2 molecule, the two bromine atoms share electrons. Since both atoms are identical bromine atoms, they have equal electronegativity, meaning they pull on the shared electrons equally.
- Pure Covalent Bond: The bond between the two bromine atoms in Br2 is a pure covalent bond. This type of bond forms when atoms share electrons equally. Each bromine atom contributes one electron to form a shared pair, completing their valence shells.
The Forces Between Br2 Molecules
While the atoms within a Br2 molecule are held together by strong covalent bonds, the separate Br2 molecules interact with each other through weaker intermolecular forces. These forces determine physical properties like melting and boiling points.
- London Dispersion Forces: Br2 molecules are held together by London dispersion forces. These are temporary, weak attractive forces that arise due to the momentary uneven sharing of electrons, creating temporary dipoles. Even though the electrons are shared equally on average in the covalent bond, at any given instant, the electron distribution can be uneven, causing a temporary dipole in one molecule. This temporary dipole can induce a corresponding dipole in a neighboring molecule, leading to a weak attraction.
- These forces are present in all molecules, but they are the only intermolecular forces between nonpolar molecules like Br2.
Summary of Br2 Bonding
To summarize the bonding in bromine:
- Intramolecular Bond: Pure covalent bond (between the two Br atoms in a molecule).
- Intermolecular Forces: London dispersion forces (between different Br2 molecules).
These London dispersion forces, although weak compared to covalent bonds, are significant enough in larger molecules like Br2 (with 70 electrons total, leading to stronger temporary dipoles) to hold the molecules together as a liquid at room temperature (-7°C melting point).
