![\"A](\"http:\/\/www.cawater-info.net\/all_about_water\/en\/wp-content\/uploads\/2015\/01\/water.jpg\")
<\/a>A stylised diagram of a water molecule. All diagrams in this post (c) me.<\/p><\/div>\n
The above diagram shows a water molecule, H2O. Two atoms of hydrogen attached to one molecule of oxgyen sharing electrons between them to form bonds. But the red lines that I\u2019ve used to show the bonds hide a far more complicated story. This may be a bond, but it is not a very equal one because while oxgyen is a nice reasonably sized molecule, with eight electrons surrounding each atom, hydrogen is tiny. It only has one electron!<\/p>\n
<\/a>A *very* stylised diagram of oxygen and hydrogen atoms with protons in purple, neutrons in pink and electrons in yellow. Physicsts and chemists are not to complain about the simplistic inaccuracies in it!<\/p><\/div>\n
So when the oxygen and hydrogen form a bond, it is not a relationship of equals. The poor little hydrogen electron can\u2019t really be part of the bond and also properly surround the hydrogen nucleus (quantum does help, but not enough). As a result the oxygen atom is nicely padded with surrounding electrons while the hydrogen atom is practically naked on one side.<\/p>\n
<\/a>Diagram showing the electron distribution around hydrogen and oxygen in a bond. The purple letters are the respective nuclei and the yellow cross-hatches represent the area where electrons are likely to be found.<\/p><\/div>\n
The little \u201cdelta plus\u201d and \u201cdelta minus\u201d at the bottom show that a small charge is generated across the bond. It\u2019s only small, but it is still big enough that there is a small positive centre at the hydrogen. Positive centres tend to attract negative charge. And where are the negative charges in H2O?<\/p>\n
<\/a>I love it when chemistry all fits together :p The red vertical lines show the attractive force between the electron-rich oxygen of one water molecule and the electron-poor hydrogen of another.<\/p><\/div>\n
This small attracting force is called a hydrogen-bond, and although it is quite weak compared to other bonds it\u2019s strong enough to make a significant difference. For example to the boiling temperature. This extra forces holding the water molecules together means that water stays liquid at room temperature whereas other very similar molecules that don\u2019t form hydrogen bonds are gaseous. This is why life on earth is water based rather than, say, hydrogen sulfide based. These hydrogen bonds also affect the solid structure of water \u2013 the bonds become more rigid as water freezes, giving ice a more open and less dense overall structure. These properties explain why ice floats on water, and how goldfish can survive at the bottom of a frozen pond over the winter.<\/p>\n
The presence of hydrogen bonds also makes water molecules more \u2018sticky\u2019 or in scientific terms cohesive and adhesive. The small charges on the water molecules allows them to stick together which is why water has a \u2018skin\u2019 that small insects can walk on, and also explains why water can be sucked up a straw so easily. It\u2019s not just straws either, plants draw water up from their roots to the top of the highest leaves without any kind of pumping mechanism. They rely on the ability of water to form a thin unbroken tube, all the way up the length of the trunk.
\nI still think trees must have a secret pump somewhere…<\/p>\n