Action of soap in removing an oily sot from a piece of cloth. Soaps are molecules in which the two ends have differing properties, one is hydrophilic, that is , it dissolves in water, while the other end is hydrophobic, that is, it dissolves in hydrocarbons. When soap is at the surface of water, the hydrophobic'tail' of soap will not be soluble in water and the soap will align along the surface of water with the ionic end in water and the hydrocarbon 'tail' protruding out of water . Inside water, these molecules have a unique orientation that keeps the hydrocarbon portion out of the water. This is achieved by forming clusters of molecules in which the hydrophobic tails are in the interior of the cluster and the ionic ends are on the surface of the cluster. This formation is called a micelle. Soap in the form of a micelle is able to clean, since the oily dirt will be collected int he centre of the micelle. The micelles stay in solution as a colloid and will not come together to precipitate because of ion-ion repulsion. Thus, the dirt suspended in the micelles in also easily rinsed away.
or
There are 18 groups and 7 periods in the modern periodic table.
(i) Atomic size and metallic character of the elements increases down a group.
(ii) Atomic size and metallic character of elements decreases from left to right in a period.
Metallic character of the element is decreased.
