Thursday, October 17, 2013

Comparison of cis-trans with E/Z

  Z   ==>  Cis isomer
  E   ==>  Trans isomer
The comparison of E-Z and Cis- Trans is suitable for above type of  isomers only. Not in all isomers. For example.

E/Z notation

E   ==>  Entgegen ( German word ). Two groups of higher priority are on opposite sides of double bond.
Z   ==>  Zusammen ( German word ). Two groups of higher priority are on same sides of double bond.
Example :
       Now we start with the cis isomer, the left end of the double bond has C and H. By the CIP priority rules, C is higher priority than H. ( Due to its higher atomic number ). In cis isomers the right end of the double bond also the same priority. Since the two priority groups are both on the same side of the double bond. Therefore this is (z) 2- butene.
        Now we look at the trans isomer, the higher priority group are on the opposite sides of the double bond. Therefore this is (E) 2- butene.



                   Isomers which have the same molecular formula and same structure but differ in the arrangement of atoms or groups in space. There are two types of stereoisomerism.

  • Geometric isomerism
  • Optical isomerism.
Geometric Isomerism:
         Isomers which arise due to the different spatial arrangement of atoms or groups around double bond or in cyclic compounds. In organic chemistry geometric isomerism otherwise known as cis/trans isomerism. Generally such isomers contain double bond , which cannot rorate, and also one form cannot be readily converted into the other form without breakage of a bond. cis and trans isomers occur both organic molecule and inorganic coordination complexes.
     The identical groups lying on the same side, the diastereomers is referred to as cis. In Latin cis means ' on the same side '
     The identical groups lying on the opposite side, the diastereomers is referred to as trans. In Latin trans means ' across ' or 'on the other side'.
     Disubstituted cyclic compounds can also exist in two different forms.
Coordination Complexes.
                     In coordination complexes cis isomers in which similar ligands are closer together and trans isomers in which similar ligands are opposite together. Not all coordination compounds have geometric isomers.
Two isomers of squar planar Pt(NH3)Cl2.
Cis isomer used in anti-tumor activity.
Trans isomer does not exhibit any anti-tumor activity.

Tuesday, October 15, 2013


         Compounds having same molecular formula but possessing different properties. This phenomenon is known as isomerism. There are two types of isomerisms.
                        ( i ) Structural isomerism.
                       ( ii ) Stereoisomerism.

Structural isomerism:
         Isomers which have the same molecular formula but differ in their structures. It is otherwise known as constitutional isomerism. It is opposed to stereoisomeris. Different types of structural isomers are given below.

  • Position isomerism.
  • Chain isomerism.
  • Functional isomerism.
Position isomerism:
         In position isomerism a functional group or other substituents changes position on a parent ( main carbon chain ) structure. It is otherwise known as regioisomerism.
Chain isomerism:
        Chain isomers differ in the structure of their chain ( carbon skeleton ). It is otherwise known as skeletal isomerism.

But pentane  C5H12  has three isomers.
Functional isomerism:
           Isomers have the same molecular formula but different functional groups are known as functional isomerism.
Example:  C3H6O 

Example: C2H6O
 CH3 – O – CH3    diethyl ether.
Carbon-oxygen-carbon chain functionality is called Ether.
 CH3 CH2 – O – H Ethanol.
Carbon-oxygen-hydrogen functionality is called Alcohol.

Wednesday, October 9, 2013

Periodic Trends Of Alkali Metals

  • Ionization Energy:
Alkali metals have low ionization energy.
                     The first ionization energies of alkali metals are relatively low and decreases on moving down the group.

   Atomic radius gets increases on moving down the group. so the outermost electron gets farther away from the nucleus and therefore the first ionization energy decreases.
   The second ionization energy of the alkali metals are high. The second most loosely held electrons is part of a fully filled electron shell and is thus difficult to remove.

  • Electropositive Character:
Electropositive character increases go down the group.
                    M      →     M+      +     1e-
     The first ionization energy of alkali metals decreases down the group, it is easier to remove the outermost electron from the atom and the participate in chemical reaction thus increasing the electropositivity down the group. The alkali metals are high electropositive that they emit electrons when irradiated with light.This effect is known as photoelectric effect. Due to this property Cs and K are used in photoelectric cells.
  • Melting And Boiling Point:
Alkali metals have low melting and boiling point.
     The weak interatomic bonds are attributed to their large atomic radii and the presence of one valance electron. The atoms increases in size going down the group. The nuclei of the ions are move further away from the delocalised electrons and hence the metallic bond becomes weaker. Therefore the melting and boiling point decreases going down the group.
  • Density:
Alkali metals have high density.

     The trends for the densities of the alkali metals depends on their atomic weight and atomic radii. The densities of the alkali metals increases moving down the group with an exception at potassium. Lithium has low density due to the low atomic weight of the atom.
  • Oxidation And Reduction:
     Alkali metals have only one electron in their outermost valence shell. So they easily lose one electron in their outermost shell and form a stable configuration of the nearest inert gas. They are monovalent elements showing an oxidation state of +1.
     Alkali metals have low ionization energy, they easily lose their valence electron. Therefore these elements behaves as good reducing agents
  • Atomic And Ionic Radii
            Atomic and Ionic radii of alkali metals are increases on moving down the group. The ionic radii of the alkali metals are much smaller than their atomic radii.

Monday, October 7, 2013

Uses of Hydrogen Peroxide

  • Hydrogen peroxide is a bleaching agent delicate materials like silk, wool, hair which wool be destroyed by chlorine, are bleached with hydrogen peroxide.
  • It act as a aerating agent in production of sponge rubber.
  • It destroys bacteria and hence it is used as an antiseptic and germicide for washing wounds, teeth and ears.
  • It is used as a oxidizing agent.
  • It is used as an Antichlor.
  • It is also used as a propellant in rockets.
  • For pollution control of domestic effluents where it restores the aerobic conditions of sewage waste for pollution control of industrial effluents containing CN-  ions. H2O2  oxidizes CN- ions to harmless product. 

Chemical Properties Of Hydrogen Peroxide

           Pure hydrogen peroxide is unstable and decomposes on standing. On heating water and oxygen are formed.
                             2H2O2     →     2H2O     +     O
Oxidizing Nature 
        It is a powerful oxidizing agent. It functions as an electron acceptor.
                              H2O2     +     2H+     +     2e-     →     2H2O
                                                                                  (In acidic solution)
                                               H2O2-     +     2e-     →     2OH-
                                                                                   (In alkaline solution)
                                              2KI     +     H2O2      →     2KOH     +     I2
                                                                                     (In neutral medium)
It oxidizes ferrous salts into ferric salts.
                           2Fe2+     +     2H+     +     H2O2     →     2Fe3+     +     2H2O
Reducing Agent :
                        Ag2O     +     H2O2     →     2Ag     +     H2O     +     O2
              Hydrogen peroxide act as a reducing agent. In above equation moist silver oxide is reduced to silver.
Addition Reaction:

Friday, October 4, 2013

Francium ( Alkali Metal )

  • Francium was discovered by Marguerite Perey in 1939.
  • Least electronegative element.
  • It occurs as a result of an alpha disintegration of actinium.
  • It can be produced by artificially bombarding thorium with protons.
  • Francium is a heavy, unstable, radioactive metal with a maximum half-life of only 22 minutes.
  • Highly radioactive.
Symbol                                 -  Fr
Atomic number                    -   87
Number of electrons            - 2, 8, 18, 32, 18, 8, 1
Electronic configuration    -  [ Rn ]7s1
Melting point                       -  300 K
Boiling point                       -  950 K
Atomic weight                     - [ 223 ]

Atomic Structure:


It is used for research purposes only. ( Due to its rarity and instability ).

Cesium ( Alkali metal )

  • Cesium was discovered by Robert Bunsen and Gustar Kirchoff in 1860. From Latin word caesius (mean- Sky blue).
  • Cesium metal is extremely reactive.
  • Cesium is the least electronegative element with a stable isotopes.
  • Cesium is found in the minerals pollucite and lepidolite.
  • Cesium form alloy with other alkali metals and amalgam with gold.
Symbol                                -  Cs
Atomic number                  -  55
Number of electrons          - 2, 8, 18, 18, 8, 1
Electronic configuration  - [ Xenon ] 6s1
Melting point                     -  301.5 K
Boiling point                     - 944 K
Atomic weight                   -  132.905

Atomic Structure:


  • Cesium is used in photoelectric cells, vaccum tubes and IR lams.
  • Cesium is used in atomic clocks.
  • Cesium hydroxide is used in etch silicon.
  • It is used as a catalyst in the hydrogenation of few organic compounds.
  • Cesium vapour is used in many common magnetometers.
  • It is also used in chemical and medical uses.
  • Cs-137 is a radioisotope used as a gamma emitter in industrial application.
  • Cs-137 is also used in hydrologic studies.
  • Cesium nitrate is used as an oxidizer and pyrotechnic colorants, to burn silicon in infrared flares.

Rubidium ( Alkali metal )

  • Rubidium was discovered by Robert Bunsen in 1861. From Latin word Rubidus ( mean, Dark red or bright red) 
  • Elemental rubidium is highly reactive and rapid oxidation in air.
  • Rubidium may be liquid at room temperature.
  • Rubidium compounds have various chemical and electronic aplications.
  • Rubidium from amalgam with mercury and alloy with gold, sodium, potassium and cesium. 
  • It is the 23rd most abundant element in the earth crust.
  • It is the second most electropositive element.
  • Occurs naturally minerals like leucite, pollucite, carnalite and zinnwaldite.
Symbol                                 -  Rb
Atomic number                    -  37
Number of electrons           - 2, 8, 18, 8, 1
Electronic configuration   -  [ Krypton ]5s1
Melting point                      - 312.46 K
Boiling point                      - 961 K
Atomic weight                     - 85.46

Atomic Structure :

  • Rubidium chloride is used in biochemistry.
  • Rubidium-87 is used in some atomic clocks to maintain accuracy.
  • Rb is used as a 'getter' in vaccum tubes and making special glasses.
  • It is easily ionised and so has possible use in 'ion engine' for space vehicles.

Potassium ( Alkali Metal )

  •  Potassium was discovered by Humphry Davy in 1807. 
  • It is derived from caustic potash ( KOH potassium hydroxide ). In Latin Kalium.
  • The metal must be stored in mineral oil, such as kerosene as it oxidizes rapidly in air and catches fire spontaneously when exposed to water.
  • Potassium ions are necessary for the function of all living cells.
  • Soft silvery white alkali metal and very reactive in water.
  • Sylvite, langbernite, carnalite and polyhalite from extensive deposits in ancient lake and sea beds from which potassium can be obtained.
Symbol                                 - K
Atomic number                    -  19
Number of electrons           -  2, 8, 8, 1
Electronic configuration   - [ Argon ] 4s1
Melting point                      - 336.53 K 
Boiling point                      -  1032 K
Atomic weight                     - 39.098

Atomic Structure:

  • Potassium is a mineral that plays many critical roles in the body.
  • Potassium is used for treating and preventing low potassium levels.
  • Potassium is in high demand as a fertilizer.
  • Metallic potassium is used in several types of magnetometers.
  • Potassium also used in food preservative, bleach textile and straw and in tanning of leathers.
  • Potassium salts have many commercial uses.

Sodium ( Alkali Metal )

  • Sodium was discovered by Humphry Davy in 1807. From the Latin name of sodanum (headache remedy)
  • It is a bright silvery metal and highly reactive than lithium.
  • Sodium floats on water, which decomposes it to evolve hydrogen and form the hydroxide.
  • It is a soft metal readily cut with the knife and is a good conductor of electricity.
  • Sodium is relatively abundant in the sun and other stars.
  • Sodium occurs in many minerals such as Cryolite, Zeolite, amphipole and sodalite.
  • It is not found free in nature.
Symbol                                -  Na
Atomic number                  - 11
Number of electrons          - 2, 8, 1
Electronic configuration  - [ Neon ]  3s1
Melting point                     - 370.87 K
Boiling point                      - 1156 K
Atomic weight                    -  22.9897

Atomic Structure:

  • Sodium vapour is used in lamps for street light.
  • It is used for manufacture of sodamide, sodium cyanide, sodium peroxide and sodium hydride.
  • Sodium compounds are used in glass, paper, chemical, soap, petroleum and metal industries.
  • It is used in the reduction of organic ester and preparation of organic compounds.
  • The alloy of sodium and potassium is ( NaK )- It is a good chemical reducing agent and heat transfer agent.
  • Sodium metal is used in the preparation of (tetraethyl lead) PbEt4 and titanium metal from PbEt4
  • Sodium chloride is important for animal nutrition.


  •  Lithium was discovered by Johann Arfwedson in 1817. From the Greek word lithose (stone). 
  • It present in trace amount in virtually all rocks.
  • Lithium metal is soft enough to be cut with a knife.
  • It appears silvery white color that quickly changes to gray due to oxidation.
  • Lithium has very low density 0.534gkm.
  • Lithium has the highest specific heat of any solid elements.
  • Lithium imports a crimson color to flame although the metal itself burn a bright white. 
Symbol                                  -    Li
Atomic number                     -   3
Number of electrons             -  2, 1
Electronic configuration    -  [ Helium ] 2s
Melting point                       -  453.69 K
Boiling point                       -  1615  K
Atomic Weight                    -  6.941

Atomic Structure:
  • Lithium batteries are disposable batteries with lithium or its compound as an anode.
  • Lithium stearate is used as a high temperature lumbricant.
  • Lithium is used in ceramic, glass, electrical and electronics, lumbricating greases and metallurgy process.
  • Lithium compound are used in pyrotechnic colorants and oxidizers in red fire works and flares.
  • Lithium is useful in the treatment of bipolar disorders.
  • Lithium chloride and lithium bromide are highly hygroscopic, so are used in drying agent.

Flame Colors in Alkali Metal

Metal                       Color
Lithium                    Crimson
Sodium                    Yellow
Potassium                Lilac
Rubidium                 Red violet
Cesium                    Blue
How the color appear ?          
          The alkali metal or any of its compounds are heated in bunsen flame, the ns' electron gets excited to higher energy levels and while return to their ground state the excitation energy absorbed by them  is released  as light in the visible region. Example: The yellow color of the sodium is a result of the energy emitted when an electrons drops from the 3p1  orbital to the 3s1 orbital of a neutral sodium atom.    

 A      -    Sodium ion in flame.
 B      -    Electron in the excited 3p orbitals.
 C      -    Emitted electron in the excited 3p orbitals to ground 3s state. ( Now the energy released as a                           yellow light)

General Characteristics of Alkali Metals

  •  Alkali metals are shiny, silver colored metals.
  • Alkali metals are very soft. Example; Lithium can be cut with a knife. Potassium can be squashed like soft butter. 
  • They tend to donate their electrons in reactions and often have an oxidation state of +1.
  • Alkali metals have low melting point and boiling point. Example : cesium melting just above the room temperature.
  • The last metal of this group francium is radioactive.
  • Alkali metals are found in nature, but not in their pure form.
  • The softness and low melting points of the alkali metals can be attributed to very weak metallic bonding in these elements.

Define: Alkali Metals

                 Group I elements are called alkali metals. Group I consist of elements like Lithium ( Li ), Sodium ( Na ), Potassium ( K ), Rubidium ( Rb ), Caesium ( Cs ) and Francium ( Fr ).The group lies in the s- block of the periodic table. Alkali metals are abundant in minerals and sea water. They are named from the Arabic word "Alquili" meaning 'plants ashes'. Ashes of plants composed mainly of sodium and potassium.