AP – SSC Physical Sciences

Question: Give Newlands table of elements. Write a brief note about the arrangement of elements in it.

Answer: Table: Newlands table of elements

Elements with similar chemical properties are to be present along a horizontal row.

Newlands was the first to assign atomic numbers to the elements. Unfortunately his work was neither accepted by his seniors nor by the journal of the chemical society, which rejected its publication.

In Newlands table of elements, if we start with hydrogen and move down and then start at the top the eighth element is fluorine and next eighth element is chlorine and so on.

The properties hydrogen, fluorine and chlorine are similar. Similarly, if you start at Lithium, then eighth element is sodium and next coming eighth is potassium and so on. These elements show similar physical and chemical properties.

Question: Collect the information about reactivity of VIII A group elements (noble gases) from internet or from your school library and prepare a report on their special character when compared to other elements of periodic table. (4 Marks)

Answer: ! VIII A group elements are noble gases or inert gases. As the name implies that they do not react with any other element under ordinary conditions.
This is because except He, other inert gas elements have stable ‘octet’ configuration. Even for He, the two available orbitals in 1s is filled with electrons and so it is also very inactive.

These elements can neither loose electrons nor gain electrons as they have very high ionization energy and zero electron affinity.
In recent times experiments have established that under suitable conditions heavier elements of this group can form compounds with F2, O2. Xenon (Xe) shows a tendency to loose an electron and exist as a positive ion. So it reacts with highly electronegative elements like F2 and O2 only.
e.g.: XeO3, XeO4, XeF2, XeF4, ………

Under favourable conditions Ar is able to form coordination compounds with BF3. The composition of this new compound is Ar.n.BF3. N.Barltel prepared xenon fluoroplatinate Xe (PlF6). This is the first compound prepared with an inert gas.

Incidentally, it is identified that these compounds have varied applications in different fields.

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Question: How do you appreciate the role of electronic configuration of the atoms of elements in periodic classification. (4 Marks)

Answer: H.J. Moseley (1913) analysed the X – ray pattern obtained when elements are subjected to bombardment by high energy electrons. Moseley realised that the atomic number is more fundamental characteristic of an element than its atomic weight.

This atomic number concept forced the periodic law to be changed. So the modern periodic law is ‘The physical and chemical properties of elements are the periodic function of electronic configurations of their atoms’.

According to the modern periodic law, the elements having same outer shell electronic configuration are kept in the same group. These elements have similar chemical properties.

This classification rectified all the short comings of Mendeleev’s
classification and also enabled the study of physical and chemical properties of elements easily.

I appreciate the usefulness of electronic configuration in arranging elements in periodic table so that the place of an element in this table can be easily identified.