<text><span class="style10">hemical Bonds (5 of 6)</span><span class="style7"></span><span class="style10">Hydrogen bonds</span><span class="style7">Some small molecules have much higher melting and boiling points than would be expected on the basis of their size. One such example is water (H2O), which has about the same mass as a neon atom but has a much higher melting point. There must therefore be unusually strong intermolecular forces between the water molecules. Although the oxygen and hydrogen atoms share a pair of electrons in a covalent bond, the oxygen atom exerts a stronger 'pull' on these electrons and so becomes electron-rich, leaving the hydrogen atom electron-poor. As a result, there is a force of attraction between hydrogen and oxygen atoms on neighboring molecules. This is known as </span><span class="style26">hydrogen bonding</span><span class="style7">.As well as accounting for the surprisingly high melting point of water, hydrogen bonding is responsible for the rigid open structure of ice crystals and is very important in influencing the structures and properties of biological molecules. Although hydrogen bonds are stronger than van der Waals forces, they are still much weaker than covalent bonds.DGE</span></text>
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<text><span class="style10"> snowflake</span><span class="style7">, magnified to 20 times its actual size. Hydrogen bonding is responsible for the characteristic hexagonal symmetry of the ice crystals in a snowflake.</span></text>
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<text>ΓÇó ATOMS AND SUBATOMIC PARTICLESΓÇó WHAT IS CHEMISTRY?ΓÇó ELEMENTS AND THE PERIODIC TABLEΓÇó CHEMICAL REACTIONSΓÇó SMALL MOLECULESΓÇó THE REACTIVITY SERIES </text>
