Chemical Structure of Water.pptx

Chemical structure OF WATER FOR B.Sc. II

1. Chemical Structure of Water Each molecule of water consists of one atom of oxygen and two atoms of hydrogen, so it has the chemical formula H 2 O. In water, each hydrogen nucleus is bound to the central oxygen atom by a pair of electrons that are shared between them; chemists call this shared electron pair a  covalent chemical bond.

2. In H2O, only two of the six outer-shell electrons of oxygen are used for this purpose, leaving four electrons which are organized into two non-bonding pairs. The four electron pairs surrounding the oxygen tend to arrange themselves as far from each other as possible in order to minimize repulsions between these clouds of negative charge.

3. In each water molecule, the nucleus of the oxygen atom ( with 8 positively charged protons ) attracts electrons much more strongly than do the hydrogen nuclei (with only one positively charged proton ). This results in a negative electrical charge near the oxygen atom (due to the "pull" of the negatively charged electrons toward the oxygen nucleus) and a positive electrical charge near the hydrogen atoms. A difference in electrical charge between different parts of a molecule is called  polarity . A polar molecule is a molecule in which part of the molecule is positively charged and part of the molecule is negatively charged. Because an oxygen atom has a greater  electronegativity  than a hydrogen atom , the O―H bonds in the water molecule are polar, with the oxygen bearing a partial negative charge (δ−) and the hydrogens having a partial positive charge (δ+).

4. This would ordinarily result in a tetrahedral geometry in which the angle between electron pairs (and therefore the H-O-H bond angle) is 109.5°. However, because the two non-bonding pairs remain closer to the oxygen atom, these exert a stronger repulsion against the two covalent bonding pairs, effectively pushing the two hydrogen atoms closer together. The result is a distorted tetrahedral arrangement in which the H—O—H angle is 104.5°. The water molecule is not linear but bent in a special way. The two hydrogen atoms are bound to the oxygen atom at an angle of 104.5°.

5. The O―H distance (bond length) is 95.7 picometres (9.57 × 10 −11  metres, or 3.77 × 10 −9  inches).

6.   Opposite electrical charges attract one another. Therefore, the positive part of one water molecule is attracted to the negative parts of other water molecules. Because of this attraction, bonds form between hydrogen positive and oxygen negative atoms of adjacent water molecules form. This type of bond always involves a hydrogen atom, so it is called a hydrogen bond . Hydrogen bonds are bonds between molecules, and they are not as strong as bonds within molecules. Nonetheless, they help hold water molecules together.

7. This bond is very weak. Hydrogen bonds are formed easily when two water molecules come close together, but are easily broken when the water molecules move apart again. They are only a small fraction of the strength of a covalent bond, but, there are a lot of them and they impart some very special properties to the substance we call water. https://youtu.be/5EZw-I65Q0A https://youtu.be/H6hMJQYsABU