The word pentoxides is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 22
Highest Scoring Words With Friends™ Play In The Letters pentoxides
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Seven Letter Word Alert: (36 words)
deepsix, denoise, denotes, depones, deposit, despite, destine, detoxes, dopiest, doxepin, epidote, episode, epoxide, epoxied, epoxies, existed, expends, exposed, exposit, extends, indexes, onestep, openest, pentode, pentose, peonies, poetise, pointed, posited, poteens, poxiest, sixteen, spinode, spondee, stipend, topside