Chemistry Modern Periodic Law and Nomenclature of Elements Having Atomic Numbers >100

Topics Covered :

● Modern Periodic Law and Present Form of Periodic Table
● Nomenclature of Elements with Atomic Numbers >100

Modern Periodic Law and the Present Form of the Periodic Table :

`=>` In `1913`, the English physicist, Henry Moseley observed regularities in the characteristic `X`-ray spectra of the elements.

● A plot of `sqrtν` (where `ν` is frequency of `X`-rays emitted) against atomic number (`Z`) gave a straight line and not the plot of `sqrtν` vs atomic mass.

● He thereby showed that the atomic number is a more fundamental property of an element than its atomic mass.

● Mendeleev’s Periodic Law was, therefore, accordingly modified. This is known as the Modern Periodic Law and can be stated as :

`text(The physical and chemical properties of the elements are periodic functions of their atomic numbers)`.

`=>` The Periodic Law revealed important analogies among the 94 naturally occurring elements (neptunium and plutonium like actinium and protoactinium are also found in pitch blende – an ore of uranium).

`=>` It stimulated renewed interest in Inorganic Chemistry and has carried into the present with the creation of artificially produced short-lived elements.

`=>` The atomic number is equal to the nuclear charge (i.e., number of protons) or the number of electrons in a neutral atom.

● It is then easy to visualize the significance of quantum numbers and electronic configurations in periodicity of elements.

● In fact, it is now recognized that the Periodic Law is essentially the consequence of the periodic variation in electronic configurations, which indeed determine the physical and chemical properties of elements and their compounds.

`=>` Numerous forms of Periodic Table have been devised from time to time.

● Some forms emphasise chemical reactions and valence, whereas others stress the electronic configuration of elements.

● A modern version, the so-called “long form” of the Periodic Table of the elements (Fig. 3.2), is the most convenient and widely used.

`text(Periods and Groups :)` The horizontal rows (which Mendeleev called series) are called periods and the vertical columns, groups.

`text(Groups or Families :)` Elements having similar outer electronic configurations in their atoms are arranged in vertical columns, referred to as groups or families.

`=>` According to the recommendation of International Union of Pure and Applied Chemistry (IUPAC), the groups are numbered from 1 to 18 replacing the older notation of groups IA … VIIA, VIII, IB … VIIB and 0.

`=>` There are altogether seven periods.

● The period number corresponds to the highest principal quantum number (`n`) of the elements in the period.

● The first period contains `2` elements.

● The subsequent periods consists of `8`, `8`, `18`, `18` and `32` elements, respectively.

● The seventh period is incomplete and like the sixth period would have a theoretical maximum (on the basis of quantum numbers) of `32` elements.

● In this form of the Periodic Table, `14` elements of both sixth and seventh periods (lanthanoids and actinoids, respectively) are placed in separate panels at the bottom.

SOME IMPORTANT CHARACTERISTICS OF MODERN PERIODIC TABLE

`=>` GROUPS:
•There are 18 vertical columns called groups.
• These groups are numbered from 1 to 18.
• Earlier these eighteen vertical groups were divided into sixteen groups designated as `IA`, `II A`, ....`VII A` ; `I B`, `II B`, ......`VII B`, `VIII` and zero.
`=>` PERIODS:
• Long form of periodic table consists of seven periods.
• These are numbered as 1,2,3,4,5,6,7 from top to bottom.
• The period number corresponds to the highest principal quantum number of the elements in the periodic table.
• The first period consists of two elements.
• The second and third period consists of eight elements each.
• Fourth and fifth period consists of 18 elements each.
• Sixth period consists of 32 elements.
• The seventh period is incomplete and like sixth would have a maximum of 32 elements.

Nomenclature of Elements with Atomic Numbers > 100 :

`=>` The naming of the new elements had been traditionally the privilege of the discoverer (or discoverers) and the suggested name was ratified by the IUPAC.

`=>` The new elements with very high atomic numbers are so unstable that only minute quantities, sometimes only a few atoms of them are obtained.

● Their synthesis and characterisation, therefore, require highly sophisticated costly equipment and laboratory.

● Such work is carried out with competitive spirit only in some laboratories in the world.

● Scientists, before collecting the reliable data on the new element, at times get tempted to claim for its discovery.

● For example, both American and Soviet scientists claimed credit for discovering element 104.

● The Americans named it Rutherfordium whereas Soviets named it Kurchatovium.

● To avoid such problems, the IUPAC has made recommendation that until a new element’s discovery is proved, and its name is officially recognized, a systematic nomenclature be derived directly from the atomic number of the element using the numerical roots for `0` and numbers `1-9`.

● These are shown in Table 3.4.

● The roots are put together in order of digits which make up the atomic number and “ium” is added at the end.

● The IUPAC names for elements with `Z` above `100` are shown in Table 3.5.


`=>` Thus, the new element first gets a temporary name, with symbol consisting of three letters.

● Later permanent name and symbol are given by a vote of IUPAC representatives from each country.

● The permanent name might reflect the country (or state of the country) in which the element was discovered, or pay tribute to a notable scientist.

● As of now, elements with atomic numbers up to 112, 114 and 116 have been discovered.

● Elements with atomic numbers 113, 115, 117 and 118 are not yet known.

 
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