UGC Net ( Environmental Science )

                                                                           UGC NET

                                                 ENVIRONMENTAL SCIENCE

                                                                          CHAPTER 1

                                                Fundamentals of Environmental Chemistry

Environmental chemistry is the science of chemical phenomenon occurring in the environmental . The study of these chemical help us to achieve equilibrium between the environmental prospects and its various biotic as well a abiotic components of matter.

Classification of Elements

1. Lothar Meyer : after studying the physical properties proposed the periodic law which states that "when elements are arranged in increasing order of their atomic weight, similarities in physical and chemical properties appear at regular interval or the physical properties of the elements are the periodic function of their atomic weight".

2. Mendeleev : In 1869  proposed that when elements are arranged in increasing order of their atomic weights, elements having similar properties, reoccurs at regular intervals.

In this periodic table, there were eight vertical columns, named as groups. There were six horizontal rows, named as periods .

He left some place for undiscovered elements in his periodic table.

3. Henry Moseley : He arrange elements by taking atomic number as the fundamental property. There are seven horizontal rows called periods and 18 vertical called groups.

 

GROUPS 

The elements arranged in vertical columns of the periodic table are called groups. 

Groups 1 Or Alkali Metals 

This group consist of the elements :

Lithium         2,1    (exists as silicate)

Sodium          2,8,1  (7th abundant metal) 

Potassium     2,8,8,1 ( 8th abundant metal)

Rubidium     2,8,18,8,1 ( self ignite in the air)

Caesium       2,8,18,18,8,1   ( self ignite in the air)

1. Na and K are mostly found in the form of their Chlorides.

2. Li ,Na and K are most vigorous reducing agents. Their hydroxides are strong bases. 

3. Na and K serve as a important role in biological activities. the nerve cell transmission depends upon the sodium and potassium ions gradients . These ions pump helps in regulating the flow of water across cell membrane and transmission in nerve signals.

 Group 2 or Alkaline Earth Metals

This group consist of the elements :

Beryllium       2,2 (occurs mainly in silicate form)

Magnesium    2,8,2 ( occurs as carbonate, sulphate, silicate)

Calcium          2,8,8,2 ( occurs mainly in carbonate )

Strontium      2,8,18,8,2 ( less abundant )

Barium          2,8,18,18,8,2 ( less abundant)

1. Mg is an important constituent of chlorophyll . Mg ions are concentrated more in intercellular than in extracellular fluids in animal bodies.

2. Ca ions are essential for the formation of bones and teeth. 

Group 3 

Scandium  

Yttrium 

Lanthanum  

Actinium

Inner transition elements (Lanthanides and actinides ) also fall in this group. it is the largest group of the periodic table containing 32 elements.  Actinium and actinoids are radioactive elements. 

Group 4

Titanium, Zirconium, hafnium and rutherfordium. The first three elements occur naturally and show similar property. 

The most characteristic oxidation state of this subgroup is +4.

Zirconium is used as cladding of fuel rods in nuclear reactor while hafnium is used in control rods for nuclear reactor.

Group 5

Vanadium, niobium, tantalum and dubnium. the first three elements of the group belong to Vanadium subgroup. The elements of vanadium subgroups occur naturally in Earth's crust.

These metals have high melting and boiling points and belong to the class of refractory metals. The oxidation state is +5. 

Group 6

These are all transition metals. The oxidation state of these elements of their compounds varies from 0 to +6. 

Group 7

Manganese is the only element in this group . Rest are found rarely on earth or produced artificially. Rhenium and its alloys with tungsten and molybdenum are used in the production of electric lamps.

Group 8

Iron, ruthenium, osmium and hassium. Iron is the second most abundant metal . These elements have high melting and boiling points. 

Group 9 

All members of this group show similar chemical behavior except rhodium. the elements of this group (except Mt) have high melting and boiling points. Compounds of cobalt are consumed in large quantities in the paint and ceramic industries. Rhodium is an important alloying agent used as a harder for platinum and palladium.

Group 10

These are all transition metals and are white to light grey in color. They posses a high luster, a resistance to tarnish are highly ductile. They exhibit oxidation state of +2 and +4.  They also act as a catalyst in the variety of chemical reaction.

Group 11 

It is also known as coinage metals. Cu, Ag and Au occur naturally while Rg is produced in laboratories. Silver is used widely in photography , medicine , agriculture.

Group 12

These elements have 2 electrons in outer most shell. Zinc and cadmium are used as a anti corrosion agents. They all are used in electrochemistry.

Group 13

These elements in this group have three electrons in their outermost shell. they are chemically reactive . Boron is less abundant in earth crust. B and Al show +3 oxidation state but stability of +1 oxidation state.

Group 14

These elements in this group have 4 electrons in their outermost shell. Each element in this group has the tendency to share these four electrons to form covalent compounds. Carbon and silicon have tetravalent nature . Germanium , tin and lead show +2 and +4 oxidation state .

Group 15

The element in this group called as nitrogen family. (N,P,As,Sb,Bi) . Nitrogen is highly abundant by volume and by mass. Phosphorus is highly abundant in crystal rocks most as orthophosphate.  

Group 16

The first four elements are called chalcogens that consist oxides, sulphides, selenides and tellurides. The metallic character increases with increasing atomic number. Oxygen and Sulphur are entirely non metallic in their chemical behavior. Selenium and tellurium are termed as metalloids. Density, melting and boiling points , covalent and ionic radii show regular increase from oxygen to polonium.

Group 17

The elements in this group are called halogen family. the element include Fluorine, chlorine ,bromine, iodine and astatine. All the elements react with metals to form salts and very reactive with non metal. The effect of size and mass which gradually increases as we go down the group. The polarizability of halogen increases as we go down the group. Fluorine and chlorine are gases, bromine is a liquid and iodine is solid.

Group 18

This group of the elements helium, neon .argon ,krypton ,xenon and radon. These are termed as inert gases. Rn (Radioactive), all the elements are found in nature. Radon is used in the treatment of cancer. Liquid He is used as cryogenic liquid. argon is used for filling bulbs.

( Group 13 to group 18 are collectively fall under P block elements of the periodic table.)

PERIODS

1. First period : Contain 2 elements. It is the shortest period.

2. Second period : ( li to Ne) . It contain 8 elements.

3. Third period : ( Na to Ar ) It contain 8 elements .

4. Fourth Period : ( k to Kr) It contain 18 elements .

5. Fifth Period : ( Rb to Xe) It contain 18 elements .

6. Sixth Period : (Cs to Rn) it contain 32 elements.

7. Seven period : ( Fr to Og) it contain 32 elements .