Structure of water

Dear students, this PPT gives the detailed structure of water.

1. Structure of Water Dr. K. GANESH KUMARI ASSISTANT PROFESSOR DEPARTMENT OF BOTANY SRIMAD ANDAVAN ARTS AND SCIENCE COLLEGE (AUTONOMOUS) TRICHY - 5

2. Topics to be covered Introduction Forms of water Sources of water Water content of organisms Distribution of water in human body Structure of water molecule

3. Water - Introduction Water is the basic molecule of life. It is indispensable for life. None of the organisms known, can exist without water. It is astonishing to see that 70% of our earth is occupied by water and in our body also about 70% of the total weight is water. The biological importance of water can be well understood by the fact that life originated in the water medium. So water is aptly described as the mother of life or soul of life. Water is the most significant molecule which connects the physical world with the biological processes.

4. Forms of Life Water exists in three forms, namely vapour or steam, solid and liquid. Above 100ᴼC, it occurs in the form of vapour or steam. Below 0ᴼC, it becomes solid called ice. Between 0ᴼC and 100ᴼC, it remains in the liquid form.

5. Sources of Water Water is available to the biological system from a number of sources such as seas, ponds, pools, lakes, rivers, streams, springs, wells, precipitation etc.

6. Water content of Organisms Age Total water % Intracellular water % Outside the cells Exatracellular water % Plasma % New born 75 35 35 5 Under 1 year 70 35 30 5 From 1 to 10 years 60 – 65 35 – 40 20 – 25 5 From 10 to 50 years 55 – 60 40 – 45 15 5 Over 50 years 50 – 55 35 – 40 10 5

7. Water content of various tissues in human body Tissue / Organ Water % Tissue / Organ Water % Adipose tissue 10.0 Muscle 75.6 Osseous tissue 22.0 Spleen 75.8 Liver 68.3 Lung 79.0 Skin 72.0 Heart 79.2 Intestine 74.3 Kidney 82.7 Brain 74.8 Blood 83.0

8. Structure of water molecule Water is an inorganic compound. The molecular formula of water is H 2 O. It contains 2 hydrogen atoms and one oxygen atom. The hydrogen and oxygen atoms are held together by covalent bonds (bonds formed by the sharing of two electrons) The three atoms in the water molecule (2 hydrogen and 1 oxygen atom) are not in a line.

9. Cont … But they are arranged in the form of a letter “V”, with oxygen atom at the tip and the hydrogen atoms at the ends of the two limbs. The bond angle between hydrogen and oxygen atoms is 105ᴼ The central property of water molecule is its electrical polarity. The oxygen atom is negatively charged and the hydrogen atom is positively charged. As this molecule has two different poles like that of a magnet, the water molecule is a dipole. In other words water is polar compound

10. Cont … The polar molecules have the property of attracting each other. Owing to this attractive force, water molecules aggregate together. As a result of this force, a water molecule can link with 4 adjacent water molecules. The linking between two water molecules is effected by the formation of a hydrogen bond (O……H) between the oxygen atom of one water molecule and the hydrogen atom of another water molecule. The oxygen atom forms a tetrahedron with the four hydrogen atoms of the neighbouring 4 water molecules.

11. Cont … Hydrogen bonds (O……H) are very weak forces having only about 1/24 th strength of covalent bonds (O-H). The four water molecules are linked to a water molecule by a 4 hydrogen bonds. These 4 hydrogen bonds are arranged tetrahedrally and consequently the water molecules in ice form a regular tetrahedral crystalline structure.

12. Cont … As the hydrogen bonds are weak, any single hydrogen bond has only an exceeding short life time. On a average each such bond last about 1/100 000 000 th of a second. So hydrogen bonds break and reform continuously. With increasing temperature, the bonds are increasingly broken.

13. Thank you