Tag: development of the modern periodic table

Questions Related to development of the modern periodic table

The arrangement of elements in a group of three is known as Law of Triads.

chemistry classification of elements- the periodic table development of the modern periodic table into the history mendeleef's periodic table

  1. True

  2. False

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Correct Option: A

Statement: In Dobernier classification of elements, the atomic weight of the middle element is equal to the average of the extreme elements of a triad.


State whether the given statement is true or false.

chemistry periodic table development of the modern periodic table into the history mendeleef's periodic table

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

Dobereiner classified the elements into triads (group of three). He made the groups such that, the mass of middle element is the average of the mass of other $2$ elements. This is Dobernier's law of triads. 


Thus given statement is $\text{true}$.

The atomic masses of Li and K are 7 and 39, respectively. According to law of triads the atomic mass of Na will be:

chemistry classification of elements- the periodic table development of the modern periodic table into the history mendeleef's periodic table

  1. 23

  2. 32

  3. 46

  4. 64

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Correct Option: A
Explanation:
Dobereiner arranged the elements in increasing order of atomic masses. He found that the atomic mass of the middle element was approximately equal to the arithmetic mean (average) of the atomic masses of the other two elements of that triad when they are arranged in their increasing order of atomic mass.

So Li=7,K=39

Atomic mass of Na = $\dfrac{7+39}{2}=\dfrac{46}{2}=23$

The attempt for classifying elements by plotting the atomic masses of elements against the atomic volumes was made by:

chemistry periodic table development of the modern periodic table into the history mendeleef's periodic table

  1. Dobereiner

  2. Newlands

  3. Lother Meyer

  4. Mendeleev

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Correct Option: C
Explanation:

According to this if the atomic weights were plotted as ordinates and the atomic volumes as abscissae-the curve obtained a series of maxima and minima-the most electropositive elements appearing at the peaks of the curve in order of their atomic weights and electronegative element at the ascending positions.

The attempt for classifying elements by plotting the atomic masses of elements against the volumes was made by:

chemistry periodic table development of the modern periodic table into the history mendeleef's periodic table

  1. Dobereiner

  2. Newland

  3. Lother Meyer

  4. Mendeleev

Show answer
Correct Option: C
Explanation:

Lothar Meyer (1869) tried to classify by plotting a graph of atomic volume versus atomic masses of different elements. 


According to this if the atomic weights were plotted as ordinates and the atomic volumes as abscissae-the curve obtained a series of maxima and minima-the most electropositive elements appearing at the peaks of the curve in order of their atomic weights and electronegative element at the ascending positions.

Option C is correct.

In Lother Meyer's curve most electronegative elements or halogens occupied ___________________.

chemistry periodic table development of the modern periodic table into the history mendeleef's periodic table

  1. Peaks.

  2. Ascending positions.

  3. Descending positions.

  4. Halogens were not shown.

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Correct Option: B
Explanation:

According to this if the atomic weights were plotted as ordinates and the atomic volumes as abscissae-the curve obtained a series of maxima and minima-the most electropositive elements appearing at the peaks of the curve in order of their atomic weights and the electronegative element at the ascending positions.

The periodic table of today owes its development to two chemists namely:

chemistry periodic table development of the modern periodic table into the history mendeleef's periodic table

  1. Rutherford and Moseley

  2. Alexander Newlands and Dobereiner

  3. Dmitri Mendeleev and Lothar Meyer

  4. de Broglie and Neil Bohr

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Correct Option: C
Explanation:

The periodic table of today owes its development to two chemists namely the Russian chemist Dmitri Mendeleev and the German chemist J. Lother Meyer. In 1869, they independently proposed that when the elements are arranged in the increasing order of their atomic weights, similarities in physical and chemical properties appear at regular intervals.

Which prediction(s) is/are incorrect according to the Lother Meyer's curve?

chemistry periodic table development of the modern periodic table into the history mendeleef's periodic table

  1. Each peak of the curve is occupied by the alkali metals

  2. Alkaline earth metals occupy ascending positions of curve

  3. Atomic volume increases first and then decreases in a period (which is defined later) in Lother Meyer's curve

  4. Identically placed elements in the atomic volume vs atomic mass curve occur in the same period in the periodic table

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Correct Option: B,C,D
Explanation:

Lothar Meyer - Meyers Curve:

1.Plotted the atomic volumes of the elements against the atomic weight, and found that the chemical properties of the element recur periodically.

2.Also notice that the elements occupying the corresponding position of the curve show similar chemical properties.

If we see the atomic mass versus atomic volume curve, we will notice the following features:

i)Alkali metals such as $Na, K, Rb$ which have similar properties occur as peaks of the curve.

ii) Halogen elements like $F, Cl, Br$ which have similar properties occur at the rising or the ascending part of the curve.

iii) Noble gasses such as $Ne, Ar, Kr$ which have similar properties occur just before the alkali elements.

So option A is correct, B,C & D are incorrect.

Hence options B,C & D are correct.