The vapour density of a mixture containing NO 2​ and N 2​ O 4​ is 38.3 at 27 °C. Calculate the moles of NO2​ in 100 mole mixture.

Dobereiner’s law of traids:

It was first attempt towards classification. He arranged similar elements in a group of three elements called triad and the atomic mass of the middle elements of the traid is approximately the arithmetic mean of the other two.

For example : Ca (40), Sr (87.5) Ba (137)

At. wt. of Sr = (40+137)/2= 88.5

88.5 is nearly similar to 87.5 of atomic wt. of Sr

Such a group of elements is called Dobereiner’s triad.

Dobereiner could arrange only a few elements as triads and there are some such elements present in a triad, whose atomic weights are approximately equal, e.g.

Fe Co Ni

Ru Rh Pd

Therefore, this hypothesis was not acceptable for all elements.

Related Questions:

(1) What are the Amphoteric metals ? gives Examples.

(2) Name of total metalloids present in periodic table ?

(3) Total numbers of elements which are liquid at normal temperature is ?

(4) What is Mendeleev's periodic table ? give important features and draw back of Mendeleev's table.

(5) What is atomic density ? give the periodicity of atomic density in periods and groups.

(6) What is atomic volume ? and what is periodicity of atomic volume in groups and periods ?

(7) Why there are 2, 8 and 8 elements in first, second and third periodic of periods table respectively ? Explain.

(8) In alkali metal group which is the strongest reducing agent in aqueous solution and why?

(9) The electron affinity of sulphur is greater than oxygen. Why?

(10) The first ionization energy of carbon atom is greater than that of boron atom, whereas reverse is true for the second ionization energy. Explain.

Lother Meyer's Curve:

(1) The graphs plotting the atomic volumes against atomic weights are known as Lothar Mayer volume

curves.

(2) The alkali metals have highest atomic volumes.

(3) Alkaline earth metals (Be, Mg Ca, Sr, Ba, etc.) which are relatively a little less electropositive. Occupy

positions on the descending part of the curve.

(3) Halogens and the noble gases (except helium) occupy positions on the ascending part of the curve.

(4) Transition elements have very small volumes and therefore these are present at the bottoms of the curve.

Example: Lother Meyer attempt was based on plotting atomic mass vs

(A) Atomic size 

(B) Atomic volume 

(C) Density 

(D) Melting point

Ans. (B)

Related Questions:

(1) What are the Amphoteric metals ? gives Examples.

(2) Name of total metalloids present in periodic table ?

(3) Total numbers of elements which are liquid at normal temperature is ?

(4) What is Mendeleev's periodic table ? give important features and draw back of Mendeleev's table.

(5) What is atomic volume ? and what is periodicity of atomic volume in groups and periods ?

(6) Why there are 2, 8 and 8 elements in first, second and third periodic of periods table respectively ? Explain.

(7) In alkali metal group which is the strongest reducing agent in aqueous solution and why?

(8) The electron affinity of sulphur is greater than oxygen. Why?

(9) The first ionization energy of carbon atom is greater than that of boron atom, whereas reverse is true for the second ionization energy. Explain.

(10) The electronegativities of B, Al, Ga are 2.0, 1.5, 1.6 respectively. The trend is not regular. Explain.

(11) Li2CO3 decomposes on heating but other alkali metal carbonates don’t. Explain.

(12) Of all noble metals, gold has got a relatively high electron affinity. Explain.

(13) Ionization energy of Boron is smaller than Beryllium even though effective nuclear charge is higher?

(14) What are the increasing order of ioni radii of first group elements in water ?

(15) What are the increasing order of molar conductivity of first group elements in water ?