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  Modern Periodic Law, Chemistry tutorial

INTRODUCTION

You well-read about efforts made by numerous scientists to systematize the knowledge they gained throughout their observations and research. The effort of these scientists resulted in the arrangement of the periodic table and the periodic law. You learned about the works of such great pioneers as A de Chancourtois, John Newlands Lothar Meyer, J. N Dobereiner, and Dmitri Mendeleev. The periodic table of nowadays has lots of similarities with that created by Mendeleev, but differs from the Mendeleev table in several significant ways. Moreover in the past, factor was named by their inventors. In various cases such a practice has led to disputes between scientists who have revealed the similar essentials working independently in different parts of the world. This has encouraged the international union of pure and applied chemists to apparatus a method for naming newly revealed elements.

Modern periodic law:

We studied how D. Mendeleev classified elements and formed his periodic table. We must have stated that there were anomalies in Mendeleev's original periodic table. There was for instance no place for lanthenides and actinides and in various instances, elements of higher atomic weight were placed before those of lower atomic weights instance Te before I and Co before Ni. He could not expect the existence of noble gases, nor could he properly place hydrogen.

Between the years 1869-1907 Mendeleev tried to develop his table. Though, the most significant enhancement of his periodic table came through the innovation of the concept of atomic number in the year 1913 via Henry Moseley, who recommended that the atomic number of an element is a more basic property than its atomic weight. Mendeleev's periodic law was thus accordingly changed. This is now recognized as the "MODERN PERIODIC LAW" and can be defined as 'the properties of elements are periodic functions of their atomic numbers'.

The Arrangement of elements in order of their rising atomic number eliminates most of the anomalies of Mendeleev's periodic table. The locations of  Co and Ni, K and Ar, Te and I do not remain anomalous any longer because atomic number not weight is utilized in arranging the elements.

Since isotopes of an element have similar atomic number, they can all be situated at one and    similar place in the periodic table. We recognize that the atomic number cannot be fractional. It rises by the integer from one element to the next. It has hence situated a boundary on the number of elements. Nowadays, 109 elements (from 1 - 109) have been revealed and any more elements which might be discovered in future will be beyond 109.

1514_morden periodic table.jpg

2114_periodictable.png

Figure: shows the modern periodic table in the form deviced by Mendeleev

Long Form of the Periodic Table:

The modern forms of Mendeleev periodic table, elements are arranged in 7 horizontal rows and 8 vertical columns. Transition and Normal elements belonging to A and B subgroup of a group were situated in one and similar column of the table.

For instance Ga and Sc together in group III A and B and Ti and Ge both in group IV A and B. In the long form of the periodic table of elements are arranged in 18 vertical columns by keeping the elements belonging to A and B subgroups in separate columns. It will be noted that in the new agreement, Sc is in group III B while Ga is now placed in group IIIA. You would have also observed that the group VIII B of Mendeleev's periodic table encloses three triads Ru, Rh, Pd (5th period), Os, Ir, Pr (1 5' period) and Fe, Co, Ni, (4th period). In the long form of the table, each element of the triad is kept in a separate column. So the group VIIIB occupies three columns of the table. We can see thus that, the long form of periodic table is an extension of the modern periodic table.

1539_Periodic Table with atomic number.jpg

Fig: Long form of the periodic table

Initially, Mendeleev gave A and B designation to the groups, having normal and transition elements, correspondingly. Though in his periodic table, this division into A and B group is frequently done arbitrarily. In different books for the elements of III to VIII groups, this designation of A and B groups is often inverted. To avoid this argument, International Union of Pure and Applied Chemistry [IUPAC] has assumed Arabic numerals 1, 2, 3 ....18 as next newest group designation in the structure of the periodic table. In this system thus, the non alkali and alkaline earth metals constitute group 1 or 2, transition elements of Sc to Zn families become groups 3, 4, 5... 12 and finally the P block elements turn into groups 13, 14....18 of the table.

Nomenclature of Elements Having Z > 100:

It has been a historical practice to let the originator of the elements to allocate the element's name. In current times, this has led to several controversies since elements with very high atomic number are thus unstable which only minute quantities of them, sometimes only one or two atoms are planned before scientists claim credit for their discovery. This has led to the questions of the reliability of the information or whether the thought new element has in fact been discovered. For instance both American and Soviet scientists claimed credit for discovering element 104. The Americans started to call it rutherfordium and the Soviet scientist started to call it Kurchotovium. To avoid this difficulty, the IUPAC has made an official suggestion that awaiting a new element discovery has been proved, a systematic nomenclature be applied according to the given IUPAC nomenclature regulations;

1. The names are derived straightly from the atomic number of the element using the given numerical root.

0

1

2

3

4

5

6

7

8

9

nil

un

bi

tri

quad

pent

hex

Sept

Oct

enm

2. The symbol of the element is composed of the original letters of the numerical roots that build up the names.

3. The root be place mutually in the order of the digit that build up the atomic number or be terminated by 'ium and ending happening in the names of the metallic elements as these are the final 'n' of enn be dropped when it occurs before 'nil' and 1' of "bi" and "tri" be dropped when it take places before "ium".

Table gives the systematic names and symbols of elements containing Z = 101 to 106 derived by application of IUPAC nomenclature rules Atomic Number Systematic Names Symbol Trivial Name.

Atomic number

Systematic Names

Symbol

Trivial Name

101

Unnilunium

Unu

Mendelevium

102

Unnilbium

Unb

Nobelium

103

Unniltrium 

Unt

Lawrencium

104

Unnilquadium

Unq

          -

105

Unnilpentium

Unp

          -

106

Unnilhexium

Unh

          -

To more development our understanding of the rules, let us work out the name of the element 101.

We start with the 1st  1 of the 101.

You have un,

Then O you have nil

Then I again you have un.

 You end it with "ium"

The name of element 101 is therefore un + nil + un +ium that is unnilunium.

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