# Question #6732d

Oct 29, 2015

Here's what's going on.

#### Explanation:

Bromine exists as a molecule rather than as a gas because it is extremely unstable in latter form.

Bromine is located in period 4, group 17 of the periodic table, and has an atomic number equal to $35$.

This means that a neutral bromine atom wil have a total of $35$ electrons surrounding its nucleus. Out of these $35$ electrons, $7$ will be located on the outermost shell, and thus be valence electrons.

Now, atoms tend to unstable with outermost shells that have fewer than $8$ electrons - this is known as an incomplete octet - so their chemical reactivity will depend on how close to having $8$ electrons on their outemost shells are.

In bromine's case, it only lacks $1$ electron to have a complete octet, so it will ty vigurously to get that one electron.

To do that, a bromine atom forms a covalent bond with another bromine atom. Each atom contributes one electron to the bond, and share these bonding electrons equally.

Hence, the bromine molecule, ${\text{Br}}_{2}$, is formed.

The interesting thing about bromine is that it is actually a liquid at room temperature.

That happens because its molecules exhibit relatively stronger London dispersion forces caused by the instantaneous and random polarizations of bromine's electron cloud.

Here's how a sample of bromine would look like at room temperature

Bromine boils at a little under ${60}^{\circ} \text{C}$, which is why the bulk of the molecules shown are still in the liquid state at room temperature.