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