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.
A principal quantum number is a number which determines the main energy level or shell in which the electron is present.It gives the average distance of the electron from the nucleus & specifies the value of the energy of the electron. The azimuthal quantum number is the number which determines the subshell in a principal energy shell to which an electron belongs.
In the periodic table of the elements, a period indicates the value of the principal quantum number (n) for the outermost shells. Each period begins with the filing of principal quantum number (n). The value of n for the sixth period is 6. For n = 6, azimuthal quantum number (l) can have values of 0, 1, 2, 3, 4.
According to Aufbau’s principle, electrons are added to different orbitals in order of their increasing energies. The energy of the 6d subshell is even higher than that of the 7s subshell.
In the 6th period, electrons can be filled in only 6s, 4f, 5d, and 6 p subshells. Now, 6s has one orbital, 4f has seven orbitals, 5d has five orbitals, and 6p has three orbitals. Therefore, there are a total of sixteen (1 + 7 + 5 + 3 = 16) orbitals available. According to Pauli’s exclusion principle, each orbital can accommodate a maximum of 2 electrons. Thus, 16 orbitals can accommodate a maximum of 32 electrons.
Hence, 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?
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