Chemistry Podcast

Saturday, 4 July 2015

Fire and Safety


It takes three things to cause a fire:
Heat - or something that is hot
Fuel - or something that will burn
Oxygen - the air that is all around us

Fire Triangle = Heat + Oxygen + Fuel

Fire Tetrahedron = Heat + Oxygen + Fuel + Chain Reaction

If we remove any one side of the triangle, the fire cannot take place.
by doing these activities-
Cooling: Remove the HEAT sources, and there is nothing hot to start the fire.
Starvation: Remove the FUEL sources, and there is nothing to burn.
Smothering: Remove the OXYGEN and the oxidation reaction stops.

Method of Extinguishment

Cooling- Removal of heat. (Best cooling media is water)
Smothering- Reducing % of oxygen. Cutting off the supply of oxygen. (Blanketing, Use foam)
Starvation- Removal of fuel or removal of combustible material.

Fire Classification: A, B, C, D, E

A: Solid Combustible Substances –wood, paper, plastic, coal etc.
B: Flammable Liquids – petrol, diesel, paint etc.
C: Flammable Gases – LPG, hydrogen, acetylene etc.
D: Metal Fire – Mg, Al, Na etc.
E: Electric Fire – Electric and Electronic equipment.

Fire Extinguisher

  1. Foam Type
  2. Dry Chemical Powder DCP and
  3. Carbon Di-Oxide

Foam Type Extinguisher:

It is a powerful flame knockout agent for contained Flammable and volatile liquid fires involving like petrol, paints and other solvents. Foam extinguishers are used to form a thick blanket of foam over the burning surface, effectively cutting off the oxygen supply there by smothering the fire and prevent re-ignition. Foam extinguishers are effective against ‘A’ & ‘B’ class of fire.

Dry Chemical Powder Extinguishers:

These are versatile and highly effective against ‘B’ & ‘C’ class fires, specially for combating three dimensional or running fires involving spilled inflammable liquids on ground like petrol, paints and gases. They can also be used on Energized Electrical Equipment’s.

Carbon Di-Oxide Fire Extinguisher: 

Carbon dioxide fire extinguishing media is highly effective against ‘B’ & ‘C’ class of fire. They can also be used on Energized Electrical Equipment’s.
What should you do if your clothes catch on fire?
Stop -> Drop -> Roll
If someone else is on fire:

  • Make sure they don’t run
  • Use a blanket to smother the fire
  • Put water on them to put out the fire

  • You can prevent your clothes from catching on fire by not getting too close to fire, take utmost care on carrying out hot jobs.

  • If you want to rescue yourself in a smoke filled area do not walk/run, crawl on the floor instead. Do not use Lift. Use stairs, rush to the windows/doors.

Discovery of protons & Discovery of Neutrons

Discovery of Protons

      =>  Discovered by E. Goldstein.
     =>  In modified cathode ray tube gives +ve charge carrying particles known as canal rays.
      =>  Lithest & smallest +ve ion obtained from Hydrogen called proton.


1)    Depend upon, nature of gas present in cathode ray tube.
2)    Charge to mass ratio of particles depends on gas from which these originate.
3)    Some of +ve charged particles carry a multiple unit of electrical charge.
4)    Behavior of protons in magnetic or electric field is opposite to election behavior.

Discovery of Neutrons

=>  Discovered by Chadwick (1932).
=>  By bombarding a thin sheet of beryllium by alpha particles.
=>  Electrically neutral particles were emitted known as neutrons.

Friday, 3 July 2015

Kossel Lewis Approach to Chemical Bonding and

Kossel Lewis Approach To Chemical Bonding

                                                                        Lewis discussed that atoms achieve stable octet when they linked by chemical bonds.
·        In  NaCl, an electron transfer from  Na to Cl and give Na+ and Cl-  ions and ,
·        In case of Cl2,H2,F2,  sharing of electron takes place to complete stable outer octet.
·        Valence electrons take part in chemical reaction or combination.
·        Symbol to represent valence electron in atom is known as Lewis symbol.
chemistry notes info      

·        Significance of Lewis symbol

To calculate valence = (no. Of dots and or / eight minus no. Of dots)

Octet Rule

                    According to this rule , atoms can combine either by sharing electron or by transfer (gaining or losing ) of electron to complete octet (i.e. 8 electron in outer most shell).

Thursday, 2 July 2015

Periodic Trends In Physical & Chemical Properties

Periodic Trends In Physical Properties

1.     Atomic Radius :- 

·        “Atomic radius decreases with increases in atomic no. in a period” because within the period, the outermost electrons are within the same valence shell. Also effective  nuclear charge increases with increase in atomic no. results in increased attraction force between nucleus and outer electrons .
·        “Atomic radius increases with increase in atomic no. in a group” because of filling of inner orbital’s with electrons which serve to shield the outer electron from the attraction of nucleus, so size of atom increases.      

2.     Ionic Radius :- 

                       On general, the trend of ionic radius is  same as that of atomic radius.
·        In ions lose of gain of electron takes place while no charge in nuclear charge.
·        Size of cation (A+) is smaller than its parent atom due to loss of electron.
·        Size of anion (A-) is large than its parent atom due to gain of electron.

3.     Ionization Enthalpy  :- 

                                   Quantitative measure of tendency of an element to loose electron is known as ionization enthalpy.
·        Ionization enthalpy is always +ve.
·        2nd ionization enthalpy is higher than 1st ionization enthalpy.
·        Alkali metals have lowest and noble gases have highest ionization energy.
·        Ionization enthalpy increases on going left to right in a period.
·        And decreases on Moring downwards in a group.
Notes of Chemistry by

4.     Electron Gain Enthalpy  :- 

                                         When an electron is added to a neutral gaseous atom to convert it into a  - ve ion, the change in enthalpy in the process is given by electron gain enthalpy.
Electron Gain enthalpy

It may be exothermic or endothermic reaction.
·        Halogens show exothermic reaction & have height – ve electron gain enthalpy.
·        Noble gases show endothermic reactions & have lowest +ve electron gain enthalpy.

5.     Electronegativity: - 

                              The qualitative measure of ability of atom to attract shared electrons from chemical compound (or chemical bond) toward itself is known as electronegativity.
·        It generally decreases down in a group and increases in a period from left to right.

Periodic Trends In Chemical Properties

1.     Trends in Valence or Oxidation States: - 

                                                                The valance or oxidation state depends on outer most orbital elements electron and / or eight minus the no. of outermost electrons.

Wednesday, 1 July 2015

Mendeleev Periodic Law, Modern Periodic Law and s, p, d, f - Block Elements

Mendeleev Periodic Law

                                      Mendeleev explanation that properties of  the elements are periodic function of their atomic weights.

Modern Periodic Law

                                       Moseley (1913) according to this law physical &  chemical  properties of the elements are periodic functions of their atomic numbers.

S - Block Elements

                            Elements of group 1 (Alkali metals) with  ns2 outermost electronic configuration.
·        These are all reactive metals with low ionisation enthalpies.
·        They lose electrons rapidly to form +1 & +2 ions.
·        Metallic character and reactivity increases on going down the group.

P - Block Elements

                               These elements belong to group no. 13 to 18.
·        These with s – block elements are called representative elements.
·        Outermost electronic configuration is varies from ns2 np1 to ns2 np6.
·        Element of group 18 (ns2 np6) are known as noble gases or invert gases.
·        Elements of group 17 known as halogens and elements of group 16 known as chalcogens.
·        Group 16 & 17 elements have high -ve electron in their outermost shell to attain stable inert gas configuration.
·        Non-metallic character increase on moving left to right in period and metallic character increases on moving down in the group.

D - Block Elements

                             These are elements of group no. 3 to 12 in centres of periodic table. Also known as the transition elements.
·        General outer most electronic configuration is (n-1)d1-10  n0-2
·        These are all metals
·        Form colours ions and show variable valences  &  par magnetism
·        Mainly  used as a catalyst
·        Zn , cd , Hg  with configuration  (n-1)d10  ns2  do not show most of the properties of transition elements.

F - Block Elements

                           These have 2 – rows of elements at bottom of periodic table.  i.e. lanthanides  Ce (z = 58)  to Lu (z = 71)  Actinides Th (z = 90) to  Lr (z = 103) .
·        Outer electronic configuration =(n-2) f1-14 (n-1) d0-1 ns2.
·        f – block elements also known as inner transition elements.


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