JON BAUGH / SCIENCE PHOTO LIBRARY JON BAUGH / SCIENCE PHOTO LIBRARY
Animation showing hydrogen bonding between molecules of ammonia (NH3). Each ammonia molecule is colour-coded to show its polarity. Each of its three hydrogen atoms has a slight positive charge (blue), while the central nitrogen atom has a slight negative charge (red). The attractive forces between these opposite charges form temporary bonds called hydrogen bonds (black lines). At the temperature of liquid ammonia, these bonds form and break constantly due to the motion of the molecules. Each ammonia molecule can form one hydrogen bond from its nitrogen atom, as the nitrogen has one lone pair of electrons. This means that even though it has three positive hydrogens, overall throughout the substance two hydrogens remain unbonded on average. This phenomenon gives ammonia many of its properties, such as its boiling point intermediate between the related compounds water and methane. Its boiling point, -33.3 degrees Celsius, is shown at bottom right. Compare this to the related compounds water and methane, in clips K004 4333 and K004 4335.
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