CHEMISTRY (Part-IV) (Railway)

The combining capacity of an atom is known as its valency.

• The number of bonds that an atom can form as part of a compound is expressed by the valency of the element.

Dry ice is solid carbon dioxide.

• It gets this name because it does not melt into a liquid when heated.
• It is commonly used as it does not have a liquid state and sublimates directly from solid state to gas state.

Ethylene is one of the world's most important chemicals, with over 60% of the raw material produced being used in the plastics Industry: HPDE, LDPE, PS and also PVC.

• Ethylene is also the key feedstock for the production of ethylene oxide.

Esters are a functional group commonly encountered in organic Chemistry.

• They are characterized by a carbon bound to three other atoms: a single bond to a carbon, a double bond to an oxygen, and a single bond to an oxygen.
• The single bond oxygen is bond to another carbon.
• Ester names are derived from the parent alcohol and the parent acid.

Mercury is both a liquid at room temperature (as it has a very low melting point of -39C) and a metal.

• Unlike all other metals, mercury atoms do not share valence electrons with other neighboring atoms.
• Rather, the electrons in mercury atoms are more tightly bound to nucleus and they move so quickly that they exhibit relativistic effects.

In the modern periodic table, the elements are listed in order of increasing atomic number. The atomic number is the number of protons in the nucleus of an atom.

Chlorine is a greenish yellow gas at room temperature and atmospheric pressure.

• It is the second halogen in the periodic table, being a nonmetal in group 17.
• It has a pungent, unpleasant, bleach-like odour that can be detected at low levels.
• It is two and a half times heavier than air.

Photosynthesis is the process used by plants, algae and certain bacteria to harness energy from sunlight and turn it into chemical energy.

•  Sunlight, chlorophyll, carbon dioxide and water are the necessary conditions required for photosynthesis.

Halite, commonly known as table salt or rock salt, is composed of sodium chloride (NaCl). The salt occurs in beds of sedimentary evaporite minerals.

The blue vitriol is also known as the Cu(II) sulphate pentahydrate or crystalline copper sulphate.

• It is used as a herbicide and a fungicide and also as an analytical reagent.