6) Liquid

The liquid state occupies an intermediate position between the gaseous and solid states. A liquid can take shape of any vessel in which it is put. liquid can’t be compressed because its molecules are close together. The change of a liquid state depends on the kinetic energy of the molecules. The higher the temperature the higher the kinetic energy. If we place one liquid layer on top of a layer of more dense liquid in which it is soluble, we shall see that two liquids begin gradually mixing. All liquids don’t flow with the same ease. Friction of molecules layers is generated by rubbing of layers of particles. The molecules of a liquid are much closer to together than they are in a gas, because of the greater reactive strength of attraction. Escaping of molecules from a liquid into its vapor is called evaporation.

7) Air

Liquid air is a mixture of liquefied gases. It is a milky liquid" owing to the presence of solid carbon dioxide and ice. Liquid air, due to its extremely low temperature, produces remarkable physical changes. If a metal vessel were cooled by liquid air, it would become so brittle that it could be crushed with the fingers. Ordinary liquid air is from one half to one fifth liquid oxygen, and therefore it can support combustion. Ordinary air contains almost constant proportions of three elementary substances, nitrogen-75.4%, oxygen-23.2% and argon-1.2% by weight.( It also contains small proportions of several inactive gases and some proportions of carbon dioxide, water vapor and dust.) The concentration of water vapour in the air is could relative humidity If the relative humidity were low, evaporation would occur rapidly. If the relative humidity were high, evaporation would occur slowly as the air is nearly saturated.

8) The nature of Polymeric Materials

Life depends fundamentally on organic polymers. These polymers provide not only food but also clothing, shelter and transportation.

Because of the complexity and fragility of their molecules, the natural organic polymers could not be analyzed until recently.

On the basis modern methods chemical and physical analysis involved a new industry of man-made organic polymers has appeared.

Synthetic polymers now available already possess several of the properties required in a structural material. The natural polymers such as proteins, cellulose and others dominated their existence, and even in ancient times people used these materials. Yet as late as the end of the 19th century polymer chemistry got little attention. It was only in the 20th century that scientists began a thorough study of these materials, using some powerful physical instruments. Their molecules were incredibly large. The giant molecules can be composed of a large number of repeating units, they being given the name "polymer".

9) Man-made Elements

Men at last understood the elements well enough to make his own.

First there were some elements still missing from the periodic table.

Scientists had to make these elements themselves. In 1919 Ernest Rutherford was the first to change nitrogen to oxygen by bombarding nitrogen atoms with alpha-particles.

Irene Curie and Fredric Joliot created a new element, radioactive phosphorus 31

The era of artificial transmutation began with the building of the first "atom-smasher", i.e.( id est) the cyclotron.

The first element produced in this way was the missing number 43, it being named "technetium.

In 1939 a new element was found. It behaved like an alkali-metal, therefore it was to be 87 the missing number of the alkali-metal family. It was called "francium".

There are also many other artificial elements, such as: "neptunium","mendelevium","nobelium",

"lawrencium" and "kurchatovium".

At the moment there are 118 elements