Question

What occurs when two fluorine atoms react to produce a fluorine molecule?

Answer 1

There is an increase in stability an increase in enthalpy and a decrease in entropy

Explanation:

The fluorine atom is unstable because it has one less electron in its outer valance shell than the stable structure of neon. When the two fluorine combine each fluorine shares its one unpaired electron with the one unpaired electron of the other atom. This provides both atoms with the stable structure of neon with 8 electrons in the outer shells

The reaction of two atoms becoming one molecule is a decrease in entropy. A decrease in entropy is by itself is non spontaneous. The general flow of energy in the universe is an increase in entropy The decrease in entropy much be balanced by an increase in energy.
The reaction is exothermic. The amount of energy contained in the the fluorine molecule is less than the amount of energy stored in the two atoms of fluorine. This energy is released into the environment.

The increase in stability drives the reaction forward as a spontaneous reaction. The increase in stability and enthalpy balances the decrease in entropy. This makes the reaction a spontaneous reaction.

Answer 2

A `"σ"` bond forms between the two nuclei and energy is released.

Explanation:

An `"F"` atom has the electron configuration `"[He] 2s"^2 "2p"_x^2 "2p"_y^2 "2p"_z`.

As the two atoms approach each other, their half-filled `"2p"_z` orbitals can overlap and form two new σ orbitals.

The two electrons in the `"2p"` atomic orbitals go into the lower-energy `σ_"2p"` bonding orbital.

(Adapted from Interactive Student Tutorial)

The `σ_"2p"` orbital is lower in energy than the original `"2p"` orbitals, so the bond formation is an exothermic process.