Available Answers

1. 1.

   Complete the statements given below pertaining to the different - Chemists and their contributions towards classification of elements by - choosing the correct words from the following list.

   [Mendeleeff, Robert Boyle, Early Chemists, Newland, Lavoisier, Doberenier, Carl Scheele, Moseley, Humphry Davy]

   1. _______________________ attempted to classify elements on basis of their properties, metallic and non-metallic nature, valency etc. but the classification was discarded and atomic weight and not properties were considered for further classification.
   2. _______________________ classified elements into groups of three on observing a relationship between atomic weights of certain elements and their properties. He arranged elements in increasing order of atomic weights in groups of three called triads.
   3. _______________________ arranged elements in series in ascending order of their atomic weights and suggested a resemblance between the eighth and first element similar to the eighth and first notes on a musical scale.
   4. _______________________ arranged elements in increasing order of their atomic weights and observed that elements with similar properties appear at regular intervals on arrangement. Such properties are called periodic properties and are those which appear at regular intervals in a periodic table. Examples of such properties are valency, electronegativity, metallic and non-metallic character.
   5. _______________________ stated that atomic number and not atomic weight of an element should be taken into consideration for classification of elements.
   6. _______________________ periodic law states that the physical and chemical properties of elements are periodic functions of their atomic weights.
   7. _______________________ arranged elements in increasing order of atomic numbers in seven horizontal rows called periods and eighteen vertical columns called groups.
2. 2.

   State the following with respect to Table 'A' and Table 'B' - pertaining to classification of elements by different scientists.

   TABLE - 'A'

   Elements	Lithium	Sodium	Potassium	Carbon	Nitrogen	Oxygen
   Atomic weight	7.0	(23.0)	39.0	12.0	(14.0)	16.0

    

   TABLE - 'B'

   Lithium	Beryllium	Boron	Carbon	Nitrogen	Oxygen	Fluorine
   7	9	11	12	14	16	19
   Sodium	Magnesium	Aluminium	Silicon	Phosphorus	Sulphur	Chlorine
   23.0	24	27	28	31	32	35.5

   1. Name the scientist whose law pertains to classification of elements as seen in Table 'A'.
   2. State the law which pertains to classification of elements as seen in Table 'A'.
   3. Name the scientist whose law pertains to classification of elements as seen in Table 'B'.
   4. State the law which pertains to classification of elements as seen in Table 'B'.
3. 3.

   Classification of elements by early chemists on basis of properties, valencies and metallic and non-metallic nature of elements was soon discarded. Give reasons.

4. 4.

   Dobercinier's Law of Triads did not hold weightage as a standard for classification for all elements. Give reasons.

5. 5.

   Newland's classification of elements led to much criticism. Give reasons.

6. 6.

   Series	Group I	Group II	Group Ill	Group IV	Group V	Group VI	Group VII	Group VIll
   1.	H = 1
   2.	Li = 7	Be = 9.4	B = 11	C = 12	N = 14	O = 16	F = 19
   3.	Na = 23	Mg = 24	AI = 27.3	Si = 28	P = 31	S = 32	CI = 35.5
   4.	K = 39	Ca =40	a* = _ 44	Ti = 48	V = 54	Cr = 52	Mn = 55	Fe=56, Co=59 Ni=59
   5.	Cu = 63	Zn = 65	b* = _ 68	c* = _ 72	As = 75	Se = 78	Br = 80

    

   The above table represents the first five periods of - Mendeleeff's original periodic table of elements.

   Answer the following with reference to Mendeleeff's periodic table.

   1. On what basis was the above classification of elements made by Mendeleeff.
   2. State the terms used for the following pertaining to Mendeleeff's periodic table.
      1. The horizontal rows of elements in the periodic table
      2. The vertical columns of elements in the periodic table
      3. The properties which repeat themselves at regular intervals in the periodic table
   3. State the contributions made by Mendeleeff which significantly helped to form the basis of the Modern Periodic Table.
   4. Give reasons why Mendeleeff's Periodic Table was not completely accepted as the Modern Periodic Table.