Question

a) Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to group 15 of the periodic table. Write the electronic configuration of these two elements. Which of these will be more electronegative? Why ? [2 Marks]

b) Compare and contrast the arrangement of elements in Mendeleev’s Periodic Table and the Modern Periodic Table. [4 Marks]

c) Write a short note on ionisation energy. [1 Mark]

Answer 1

a)
Electronic configuration of nitrogen = 2,5
Electronic configuration of phosphorus = 2, 8, 5
[1 Mark]
Nitrogen will be more electronegative than phosphorus because outermost shell is nearer to nucleus and therefore nucleus will attract electrons more strongly. And also in a group of the periodic table, electron attracting tendency decreases as we move from top to bottom. [1 Mark]

b)

Mendeleev’s Periodic Table Modern Periodic Table
(i) Elements are arranged in the order of increasing atomic mass. (i) Elements are arranged in the order of increasing atomic number.
(ii) There are nine vertical columns called groups. (ii) There are eighteen vertical columns called groups.
(iii) There is no place for noble gases. (iii) Noble gases are placed on the right hand side of the table.
(iv) There is no place for isotopes. (iv) Isotope are kept at the same place because their atomic number is same.

[4 Marks]
c)
Ionisation energy is the minimum energy required to remove an electron from an isolated gaseous atom in its ground state to form a cation. It is otherwise called ionisation enthalpy. It is measured in kJ/mol. Higher the ionisation energy, it is more difficult to remove the electron. [1 Mark]