Atomic sentences correspond to the simplest declarative sentences of English, and often consist of names and predicates.
Claire gave Scruffy to Max
In first order logic (FOL), atomic sentences can also be formed by combining names (or individual constants) and predicates, albeit according to slightly different rules.
gave(Claire, Scruffy, Max)
Different versions of FOL have different conventions for forming names and predicates and different conventions for for combining them.