The Lewis Dot Structure for H2O

Created by MakeTheBrainHappy.

This is the Lewis Dot Structure for H2O. You could alternatively also draw the structure by including two dots for every bond. While oxygen's octet seems to have been filled, hydrogen only has two electrons for its valence shell. Based on our previous discussion surrounding the covalent bonds which hydrogen forms, we know that hydrogen's valence shell only requires two electrons because it only has a 1s orbital. Therefore its valence electron is filled by oxygen sharing another electron.  

H2O's Lewis Dot Structure gives it many unique properties mostly due to the two lone pairs on the central oxygen atom. This increases electron-electron repulsion and therefore creates a bent structure as opposed to CO2's linear structure. This "bent" molecular structure gives it many unique properties such as being polar. One of the most fascinating phenomena is the idea of "hydrogen bonding" which influences water's properties dramatically.

Hydrogen bonding is a type of intermolecular force where the electronegativity difference in the oxygen atom causes a partial permanent dipole to form between the hydrogen and oxygen atoms (shown in the dashed lines). The bonds in the water molecule themselves are covalent bonds. You can learn about the difference in this post. Source

Due to the strength of these hydrogen bonds, water has a relatively high melting and boiling point, although they are not as high as network covalent solids. Those are bonded by intramolecular forces which involve the actual sharing of electrons vs. partial dipole forces in hydrogen bonds. There are only three types of bonds which can hydrogen bond. These are N-H, O-H, and F-H bonds due to the large electronegativity differences between the molecules.

NH3 is another molecule which creates similar hydrogen bonds as H2O. Source

What other properties does water have?

Water is one of the only elements to be found in all three states (solid, liquid and gaseous) naturally on earth. Hydrogen bonding causes a crystalline structure which makes it less dense than liquid water. This is why ice floats in the oceans. Water has also a high surface tension and adhesion. Cohesion and adhesion are essential for plants who manipulate these processes to move water from the roots to the leafs to support the growth of the plant. All this is caused by the simple structure of H2O, represented by the Lewis Dot Diagram above.

Water molecules in all three states of matter. Source

Source:
https://pubchem.ncbi.nlm.nih.gov/compound/water