Why can methyl radicals form ethane during a chain-termination step?

Methyl radicals ($·{\text{CH}}_3$) are highly reactive species because they contain a single, unpaired electron. In chemical chain reactions, these radicals are typically transient intermediates that seek to pair their odd electron to achieve a stable electronic configuration.12

During a chain-termination step, two methyl radicals collide and combine with one another. Because each radical carries a single unpaired electron, their interaction allows them to form a new, shared covalent bond, resulting in the production of ethane (${\text{H}}_3{\text{C—CH}}_3$). This process, known as dimerization, effectively removes the reactive radicals from the reaction mixture, thereby terminating the chain.12