Telangana SSC Physical Sciences

10th Class Physical Sciences Imp Questions – Elements

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Q: How do the values of electron gain enthalpy change in a group, in a period and in metals? (2 Marks)

Answer: Electron gain enthalpy values decrease as we go down in a group, but increase along a period from left to right. Metals have very low electron gain enthalpy values and alkaline earth metals have even positive values.

Note that the negative sign for energy value in table indicates that energy is liberated or lost, and the positive sign tells that the energy is gained or absorbed. All the factors which influence the ionization energy would also influence the electron gain enthalpy.

Question: Explain the term ‘electronegativity’. What factors influence it?

Answer: The electronegativity of an element is defined as the relative tendency of its atom to attract electrons towards it self when it is bonded to the atom of another element. All the factors that influence the ionization energy and the electron affinity of elements influence the electronegativity values of these elements. Because of this, Millikon proposed that the electronegativity of an element is the average value of its ionization energy and electron affinity.

Question: How does the value of electronegativity vary as we go down a group or across a period? (2 Marks)

Answer: Electronegativity values of elements decrease as we go down in a group and increase along a period from left to right. The most electronegative element is ‘F’. and the least electronegative stable element is ‘Cs’.

Question: Write a note on the properties of ‘metals’ and ‘non – metals’. (4 Marks)

Answer: Metals generally show less electronegative character. In compounds, they generally show a tendency to remain as positive ions. This property is often termed as electropositive character. Metals are electropositive elements.

Non metals are generally more electronegative due to their smaller atomic radii.
Let us examine the elements of 3rd period.
3rd period: Na Mg Al Si P S Cl.

We know that Na and Mg are metals; Al and Si are semi metals (metalloids);
P, S and Cl are non metals. So we find metals on left side and non metals on right side of the periodic table. This metallic character decreases while non metallic character increases as we move along a period (from left to right)
Let us take group 14 (IV A) elements.
IV A group: C Si Ge Sn Pb

Here also we know that carbon is non metal, Si and Ge are metalloids, Sn and Pb are metals. So we find non metals particularly at the right hand side top and metals at the left and right hand side bottom of the periodic table. This means metallic character increases while non metallic character decreases in a group as we move from top to bottom.

10th Class Physical Sciences – 4 Marks Imp Questions – Classification of Elements

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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.

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