CHEMISTRY (Part-IV) (Railway)

Lead is a chemical element with the symbol Pb (from the Latin plumbum) and atomic number 82.

• It is very soft, highly malleable, ductile, and a relatively bad conductor of electricity.

J.J. Thomson's experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons.

Thomson's plum pudding model of the atom had negatively-charged electrons embedded within a positively-charged 'soup'.

All living things contain carbon in some form.

• Carbon is the primary component of macromolecules, including proteins, lipids, nucleic acids, and carbohydrates.

Valence electrons are those electrons that reside in the outermost shell surrounding an atomic nucleus. It is a negatively charged particle.

• Valence electrons participate in the formation of a chemical bond.
• The presence of valence electrons can determine the element's chemical properties.

Radioactivity was discovered in 1896 by the French scientist Henri Becquerel, while testing phosphorescent materials with photographic plates.

• He discovered that, when the plates were covered with black paper, that phosphorescent materials did not affect the plates until he used uranium salts.

Diffusion is a process through which oxygen can move across the plasma membrane.

• Oxygen and carbon dioxide move across cell membranes via simple diffusion, a process that requires no energy input and is driven by differences in concentration on either side of the cell membrane.

Muriatic acid is one of the names for hydrochloric acid, a corrosive strong acid.

• It is also known as spirits of salt or acidumsalis.
• "Muriatic" means "pertaining to brine or salt".
• The chemical formula for muriatic acid is HCl.

Gallium arsenide (GaAs) is most generally used in the production of a solar cell as it can absorb relatively more energy from the incident solar radiations because of the relatively higher absorption coefficient.

• This is the reason why the gallium arsenide has not been used in the production of a solar cell.

Chlorophyll is a green-colored pigment that in plants absorbs light for photosynthesis.

•  In order to absorb the blue color of light in the greatest quantity, the maximum intensity of photosynthesis occurs in red light.

Some elements behave chemically both as metals and nonmetals, and are called metalloids.

• Their examples include Boron, Silicon, Germanium and Antimony.
• Elements which are neither metals nor non-metals are called Noble Gases.