The values of gas transport coefficients, when both unbound particles and bound pairs are present, are standardly accounted for by treating the gas as a mixture of free atoms and bound pairs and using the well-known expressions for the transport coefficients for a mixture. But since the bound pairs consist of two atoms, it should also be possible to start from a purely atomic picture of the gas. This paper accomplishes that aim, starting with the time correlation function expression for the transport coefficient in terms of atomic variables.