Category: SCIENCE BLOG

Introduction. The origin of CFCs could be traced to the miraculous refrigerant, freon – 12 , discovered in 1930 by scientists in the Frigidair Division of General Motors in US . Chlorofluoro carbons were introduced to replace the toxic and inflammable refrigerants such as methyl chloride, propane and sulphur dioxide. They were hailed as miracle chemicals because of their non-toxic, non-inflammable and stable nature. CFC’s have low viscosity, low surface tension, low boiling points and least reactivity. Later on when low pressure valves were developed CFCs became standard propellants for dispensing aerosol.
A series of CFCs were developed by Du Pont in 1940 to use these compounds in refrigeration and air conditioning. By 1950 CFCs were widely used for refrigeration, air conditioning, aerosol propellants, cleaning solvents, in dry cleaning, plastic forms, for sterilizing surgical instruments etc. Since 1955, their production has increased progressively reaching to 1.7 billion in 1973. CFCs are widely used because of their low boiling points ranging from 48°C (CFC -113) to -39°C (CFC-115). But during the last decade, they were found to be responsible for ozone depletion in the stratosphere.
Bromine containing halons were developed by the US Army Corps of Engineers during second world war as a means of fighting in tanks. Halons are gaseous halogen compounds which are 3 to 10 times more damaging to the ozone layer than CFCs.
Nomenclature of CFCs. Consider C F C
a b c
where a = number of carbon atoms -1 (usually omitted if a = 0) , b = number of H atoms + , c = number of F atoms. For saturation c consists of chlorine.

To determine the chemical formula. Consider CFC-115 . Add 90 to this number 115+90 = 205 . The number 205 shows 2 carbons , 0 hydrogens and 5 fluorines. The remaining one atom for carbon saturation is chlorine . Thus chemical formula of CFC -115 is CF3CF2Cl
Some examples are :
C H F Cl Formula
F-12 12+90=102 1 0 2 2 CF2Cl2
F-22 22+90=112 1 1 2 1 CF2HCl
F-124 124+90=214 2 1 4 1 C2F4HCl

Bohr could not give the reason of whole number of n in angular momentum
mvr = nh/2π equation
de- Broglie assumed that in the phenomenon of interference or diffraction the distance covered by electron should be integral multiple of wavelength (λ) . Since electron moves in circular path so it can move in only in those orbits whose circumference is some integral multiple of wavelength. Therefore,
2πr=nλ ……………….(a)
or 2πr =n.h/mv
or mvr = nh/2π …………………(b)
Above equation (b) is nothing but the Bohr’s hypothesis for circular motion of electron. Thus de-Broglie gave logical explanation of Bohr’s concept Fig. gives the Bohr’s and de-Broglie’s circular paths of electron. If nλ (5 λ) is a whole number, only then eaves will be in phase (fig. a), otherwise they will not be in phase (fig.b) in which n is not whole number. It means orbit (fig. b) is not allowed.

Conclusions from de-Broglie’s Equation : Following conclusions may be drawn from the de-Broglie’s equation .
de-Broglie’s wavelength λ is significant only for very minute particles like electron , photon etc. It is not significant for heavier particles for which mass (m) is very large so wavelength will be almost negligible (since λ = 1/m)
Wavelength is inversely proportional to the velocity of the particle Thus; wavelength for a stationary particle is indeterminate.
Wavelength does not depend upon the nature and charge of particle.
De-Broglie’s wave (matter waves) are entirely different from electromagnetic waves).