Cov hlau tsis muaj roj yog cov roj av lossis cov khoom tawg yooj yim lossis cov kua dej uas tsis muaj cov khoom siv hlau nyob rau hauv ib txwm muaj, xws li 15 lub ntsiab lus nyob rau sab xis ntawm lub rooj zaum thiab hydrogen, cov ntsiab lus ntawm pawg xoom. Feem ntau ntawm cov non-metal atoms muaj ntau valence plhaub s, p electrons, tuaj yeem tsim cov roj diatomic molecular gas los yog pob txha, saw lossis txheej txheej macromolecular crystal qauv.
