A hydrogen bond forms when hydrogen is covalently bonded to
- A. carbon, silicon or sulphur
- B. any halogen
- C. a metal
- D. a small, highly electronegative atom such as fluorine, oxygen or nitrogen
Explanation
The electronegative atom pulls electron density away, leaving the hydrogen nucleus unusually exposed so that it attracts a lone pair on a neighbouring molecule. Only fluorine, oxygen and nitrogen are small and electronegative enough for the effect to be strong. Carbon is not electronegative enough, which is why hydrocarbons show no hydrogen bonding and are gases or volatile liquids.