How to pronounce atoms in American English

Stress falls on the first syllable — say "A" with a longer, fuller vowel and keep every other syllable short and quick. The respell "A-tuhmz" marks the stressed syllable in capitals so the rhythm is easy to read at a glance.

In American English, when /t/ sits between two vowels with the second one unstressed, it turns into a quick D-like flap. So "atoms" sounds closer to "A-tuhmz" than to a crisp-T pronunciation. This is the flap-T rule, one of the most distinctive sounds of casual American speech.

Unstressed syllables in American English collapse toward a schwa — a lazy, neutral "uh" sound. The full vowel is what textbooks teach, but in actual American speech every unstressed vowel reduces. The respell "A-tuhmz" shows the reduced form so you can hear the casual rhythm directly.

American English uses different vowel shapes, a relaxed retroflex R, and connected-speech tricks like flap-T and glottal-stop T that British Received Pronunciation generally avoids. The respell "A-tuhmz" reflects the casual American form; British dictionaries typically print a citation form with crisper consonants and different vowel choices.