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 ?

Connected Containers: Problems:

(1) Two vessels A and B with rigid walls containing ideal gases. The pressure, temperature and the volume are P_A, T_A and V in the vessel A and P_B , T_B and V in vessel B . the vessels are now connected through a small tube. P/T value is equal to.

(2) Two closed bulbs of equal volume (V) containing an ideal gas initially at pressure Pi and temperature Ti are connected through a narrow tube of negligible volume as shown in the figure below. The pressure of one of the bulb is raised to T2. The final pressure is: (JEE Mains-2016)

(3) A closed tank has two compartments A and B, both filled with oxygen (assumed to be ideal gas). The partition separating the two compartments is fixed and is a perfect heat insulator (Figure 1). If the old partition is replaced by a new partition which can slide and conduct heat but does not allow the gas to leak across (Figure 2), the volume (in m3) of the compartment A after the system attains equilibrium is--- (IIT-Ad-2018)

(4) The stop-cock connecting the two bulbs of 5dm3 and 10dm3 contains an ideal gas at 10 bar and 10 bar respectively is opened. Thus final pressure if two bulbs opened at the same temperature is

(5)Two vessels A and B with rigid walls containing ideal gases. The pressure, temperature and the volume are P_A, T_A and V in the vessel A and P_B , T_B and V in vessel B . the vessels are now connected through a small tube. P/T value is equal to.