whereas /ˌweərˈæz/ is written as one word. Dictionaries such as Cambridge list it as a single headword, a conjunction.
Note the final syllable: eas spells /əz/, a reduced vowel, not /iːz/. Unstressed syllables often weaken to /ə/. She walks to work, whereas I cycle.
The conjunction is never split. When writers produce where as, the string breaks down as the adverb where plus as in a different structure.
Where you hear it
The south is sunny, whereas the north gets rain. Say it /ˌweərˈæz/, one continuous word, with the stress landing on the second syllable.
The US entry also gives a form with no /h/ at the start, /werˈæz/, alongside the variant /hweərˈæz/ with a light /h/ puff. Both stress the second syllable, and both match the single written form whereas. The transcriptions tell you how it sounds, though, not how it is written; spelling and pronunciation have to be checked separately.