0The unusual properties of water are due to the strong attractions between adjacent water molecules, which gives the water great cohesion. It also has adhesion properties to other molecules. Each hydrogen atom of a water molecule shares an electron pair with an oxygen atom. The shape of the water molecule is dictated by the outer electron orbitals of the oxygen atom; these orbitals describe a rough tetrahedron with a hydrogen atom at each of the two corners and unshared electrons on the other two corners.
Bonds :
The H-O-H bond angle is 104.5 degrees slightly less than 109.5 degrees. It is because the nonbonding orbitals of oxygen slightly compress the orbitals shared by hydrogen. A hydrogen bond is formed between the two molecules of water in which O of one molecule shares electrons with H of another water molecule. (O-H). Another bond as seen in the fig. is between the H and O of the same molecule intermolecular bond (covalent bond) so, two covalent bonds.
Hydrogen bonds are weaker than the covalent bonds. It's easy to break hydrogen bonds than covalent bonds. At room temperature, the thermal energy which is defined as the kinetic energy formed by the movement of the individual atoms and molecules is of the same order as that of the energy required to break hydrogen bonds.
Dipoles in water molecule:
The sharing of electrons between the oxygen and hydrogen are unequal, which leads to the negative charge on oxygen and a positive charge on the hydrogen.
Why does Ice float on the water?
At any given instant, in liquid water at room temperature, each water molecule forms hydrogen bonds with 3.4 other water molecules. So the water molecules in liquid form are in continuous motion making and breaking the hydrogen bonds rapidly. Whereas in the solid form, each molecule of water makes four hydrogen bonds with the other water molecules. It is because of the nearly tetrahedral arrangement of the orbitals about the oxygen atom.
So, a solid form of a crystal structure is formed which occupies more space in the structure than the water molecules in the liquid phase which are condensed.
It is reverse to the normal three states of matter concept that solids have condensed molecules, liquids have loosely packed molecules.
