Short Answer TypePredict the formulae of the stable binary compounds that would be formed by the following pairs of elements:
calcium and iodine
Predict the formula of the stable binary compounds which would be formed by the following pairs of elements:
(i) element 114 and fluorine
(ii) element 120 and oxygen.
Long Answer TypeDiscuss briefly the anomalous behviour of elements of second period.
Or
The first element of each group differs significantly from rest of the elements of the same group. Give reasons.
Short Answer TypeShow by a chemical reaction with water that Na2O is a basic oxide and Cl2O7 is an acidic oxide.
What is the basic difference in approach between the Mendeleev’s Periodic Law and the Modern Periodic Law?
Long Answer TypeOn the basis of quantum numbers, justify that the sixth period of the periodic table should have 32 elements.
Short Answer TypeLong Answer TypeAmong the second period elements the actual ionisation enthalpies are in the order
Li<B<Be<C<O<N<F<Ne.
Explain why
(i) Be has higher 
than B
(ii) O has lower 
than N and F?
i) In case of Be ( 1s2 2s2) the outermost electron is present in 2s- orbital while in B(1s22s22p1). IT is present in 29-orbital. Since 2s- electrons, due to greater penetration, are more strongly attracted by the nucleus than 2p-electrons, therefore, more amount of energy is required to knock out a 2s-electron than a 2p-electron. Consequently, of Be is Higher than that of of B.
ii) The electronic configuration of N(1s2 2s2 2p1x 2p1y 21z) in which 2p-orbital are exactly half filled is more stable than the electronic configuration of O( 1s2 2s2 2p2x2p1y 21z) in which the 12p-orbital are neither half filled nor completely filled. Therefore, it is difficult to remove an electron from N than from O. As a result, of O is less than that of N. Because of higher nuclear charge(+9) and smaller atomic size, the first ionization enthalpy of F is higher than that of O. Therefore, ionization enthalpy of O is less than that N as well as of F.
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