Most English speakers are flexible on where syllables get split, especially unstressed ones. Both a-tom and at-om sound fine to me. I could also see ay-tom in s

Most English speakers are flexible on where syllables get split, especially unstressed ones. Both a-tom and at-om sound fine to me. I could also see ay-tom in some North American dialects (if this seems ridiculous, ay-tomic is more mainstream, ay-tonal is standard).