Structural Biochemistry/Polarity

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The Structure of Water[edit]

Water consists of two hydrogen atoms connected with one oxygen atom. The hydrogen atoms are connected to the oxygen in a covalent bond manner by sharing two electrons together. The structure of oxygen is that surrounding it there is the presence of two unpaired electrons. Oxygen is significantly more electronegative than Hydrogen, meaning that has a greater tendency to attract electrons.

3D model hydrogen bonds in water.svg


Polarity and Hydrogen Bonding[edit]

Tetrahedral bond network, a special property of water [1]

As a result of this uneven distribution of electron density, water is polar. Both of the hydrogens have a partial positive(Delta+) and oxygen has a partial negative (Delta-) due to oxygen holding the shared electrons closer to itself and away from hydrogen. This attraction between the partial positive and partial negative creates what is known as a hydrogen bond. Hydrogen bonding only occurs when hydrogen is bonded with electronegative atoms such as oxygen, fluorine, or nitrogen, so this type of a bond is very unique.
The oxygen carrying partial negative charge can form hydrogen bonds with two neighboring hydrogen atoms and each hydrogen atoms in the water molecule can form one hydrogen bond with other electronegative atoms. So typically each molecule of water is able to bond with four of the neighbors in the proximity to form what is known as a tetrahedron network.

Indissolubility of molecules and ions in water because of its polarity. Another unique characteristic of water resulting from hydrogen bonding is that water is lighter in the solid state. The reason for that is because the hydrogen bonds keep water molecules in certain distance away from each other when water freeze. When water is in liquid state, hydrogen bonds form and break, then reform again constantly in the space. Making the density of water higher in liquid state.

In fact, water is extremely polar solution because it has the polar O-H bond. Given that oxygen has an extremely high electron affinity compared to hydrogen, oxygen will tend to pull the electrons away from the hydrogen atoms in the molecule. The massive polarity of the O-H bond is the result of this electron affinity.