Water Molecule Chemical Structure
Water molecule, chemical formula H2O, formed by chemical elements oxygen and hydrogen, existing in our earth environment in crystalline solids, liquid solutions, and gaseous form. A tasteless, colorless, v-shaped water is an important liquid substance that has the ability to dissolve many organic and inorganic compounds or chemical elements in chemistry. Liquid and solid states of water arise due to extensive hydrogen bonding with molecular weight 18 gm mol-1, melting point 0°C, boiling point 100°C, and essential compound for the living organisms. The availability of hygienically safe and pure drinking water solution for home uses is a big problem all over the world and we used many techniques for conservation it. sewage disposal, industrial wastage, sulfuric acid, nitric acid, fertilizer, insecticides, and detergents are the main pollutant causes for water pollution in recent days.
A small quantity of water appears colourless but due to the atomic absorption of red light or wavelengths, it has a blue colour liquid. Water in our earth environment appears in two forms like hard and soft solutions, according to the dissolving minerals levels or different types of metal ions (calcium, magnesium, aluminum). Due to the formation of acid rain and dissolving materials, the pH scale and hardness or softness levels of water solution change in the present day that harmful effects on the biological systems of plants and animals. The amphiprotic substances, water acts as an acid in presence of acidic materials but alkaline in presence of base materials.
Shape of Water Molecule
The valance shell electronic configuration of the oxygen atom in the water molecule, 2s2 2px2 2py1 2pz1. All these four atomic orbitals hybridize to form four equivalent sp3 tetrahedral hybrid orbital. Two of these four hybridized orbitals contain singly occupied electron particles. Therefore, these two orbitals overlap with two 1s-orbital of the hydrogen atom to form two covalent bonds. Another two orbitals contain two lone pairs. Due to the presence of lone pairs on the central atom, water is a v-shape molecule with the H-O-H bond angle of 105.5°.
The electronegativity and electron affinity of oxygen is much greater than the hydrogen in the periodic table. Therefore, the electric polarization measurement for distilled water molecule arises due to two facts, the bond polarity or dipole moment due to oxygen-hydrogen electronegativity differences, the presence of the lone pair in the central atom.
Crystal Structure of Ice
The crystal structure of ice and water represented the different types of complex dimensions in chemistry. In ice molecule, at least nine complex crystal lattices are established according to the different range of temperature and pressure. The ordinary forms of distilled water on freezing point or 0°C and 1 atm pressure consists of puckered hexagons. In this structure, each H2O-unit surrounded tetrahedrally by the oxygen atoms of four other H2O molecules through hydrogen bonds extended over the entire structure. In ice crystal, there are huge void or empty spaces. Each oxygen atom has two near and two distant neighbors. The experimental zero-point entropy of ice 3.4 j mol-1 with very low density and very low temperature of about -120°C, cubic lattice of ice is observed.
When the number of H2O molecules brought together, the positive end of one dipole attacks the negative end of the other dipole. Therefore, H2O molecules associated together to form the cluster (H2O)n in liquid form but in the gas phase of the water molecule, no such hydrogen bonding or association found.
Acid Alkali solutions
Due to the migration of hydrogen ion from H3O+ ion, the life in individual H3O+ ion is very low or the proton is readily transferred to a base in the solution. Therefore, the acid-base neutralization process in water involves the diffusion of the proton to the base. The chemical equilibrium reaction of H2O is written as, H2O → H+ + OH–.
Therefore, the ionic product, kw = k [H2O] = [H+] [OH–]. The ionization product of water is constantly equal to 10-14, or aqueous solution the concentration of hydrogen and hydroxyl ion are inversely proportional to each other. Therefore, pure water solutions function as an acid towards acid-like nitric acid, sulfuric acid, acetic acid solution, and an alkaline toward the base like sodium hydroxide, potassium hydroxide, etc.
Hard and Soft Water Solution
The universal solvent water categories into two types, hard and soft, according to dissolved mineral content, some of these minerals are beneficial for our health. The hard H2O solution contains common calcium and magnesium salt that produces insoluble precipitates with shop material. Calcium and sodium bicarbonate makes the solution temporarily hard. When the solutions contain soluble sulfates of calcium or magnesium which are not precipitated by boiling are called permanent hard water.
On boiling, the temporary hardness of the water solution can remove but not the permanent hardness of the salt solution. Therefore, in learning chemistry, hard solutions are made soft by passing it through beds of insoluble aluminum sodium silicates or ion exchange resin (zeolites). The useful regent likes EDTA or ethylene diamine tetra-acetic acid or Calgon (sodium hexametaphosphate) are used in removing the hardness (magnesium, potassium, calcium salt) from the water solution or softener system.