What is a periodic property? How do the following properties change in a group and period? Explain.

(a) Atomic radius

(b) Ionization energy

(c) Electron affinity

(d) Electro negativity.

(b) Explain the ionization energy order in the following sets of elements:

a) Na, Al, Cl b) Li, Be, B

c) C N, O d) F, Ne, Na c) Be, Mg, Ca

Periodic property: The modern periodic table is organized on the basis of electronic configuration of the atoms of elements.

Physical and chemical property of elements are related to their electronic configurations particularly the outer shell configuration.

a. Atomic radius

Atomic radius goes on decreasing while going from left to right in a period because of the following reasons:

i. Within a period, the atomic number increases one by one as a result nuclear charge increases.

ii. The outer electrons are adding in the same valence shell.

iii. Due to increased nuclear charge, the attraction of electrons by the nucleus increases.

iv. Therefore, the size of the atom decreases with the increase in atomic number (number of protons).

Atomic radius goes on increasing down a group because:

i. Down a group, the atomic number increases one by one as a result nuclear charge increases.

ii. The outer electrons are adding in a new valence shell.

iii. Therefore, the distance between the outermost electron (valence electron) and the nucleus is also increasing

iv. Therefore, the size of the atom increases with increase I atomic number.

b) Ionization energy

Ionization energy goes on increasing as we move from left to right because:

⇒ The attraction of electrons towards the nucleus increases with increase in atomic number.

⇒ Thus, the electrons are bonded tightly by the nucleus.

⇒ It becomes difficult to remove electrons.

⇒ Thus, ionization energy increases.

Ionization energy goes on increasing as we move from top to bottom because:

⇒ The outer electrons are adding in a new valence shell.

⇒ Therefore, the distance between the outermost electron (valence electron) and the nucleus is also increasing

⇒ It becomes easy to remove electrons.

⇒ Thus, ionization energy decreases.

c) Electron affinity

Electron affinity goes on increasing as we move from left to right because:

⇒ The nuclear charge increases from left to right so it easier to add an electron.

⇒ Thus, it increases along a period.

Electron affinity goes on decreasing as we move from top to bottom because:

⇒ The size of the atom increases.

⇒ The added electron becomes farther from the nucleus as we move

⇒ Thus, it decreases as we down in a group.

d) Electronegativity

Electronegativity increases along a period because-

⇒ The atomic radius goes on decreasing as we move from left to right due to which the attraction between the outer electrons and nucleus increases.

Electronegativity decreases along a group because-

⇒ The atomic radius goes on increasing as we move from top to bottom due to which the attraction between the outer electrons and nucleus decreases.

(b) a) The ionization energy increases as we move from left to right in a period. Thus, the ionization energy follows in the given order:

Na < Al < Cl

b) The ionization energy increases as we move from left to right in a period. Thus, the ionization energy follows in the given order:

Li < Be < B

c) The ionization energy increases as we move from left to right in a period. Thus, the ionization energy follows in the given order:

C < N < O

d) Ionization energy increases as we move from left to right in a period and decreases as we move down the group.

By combining these two facts, the ionization energy follows in the given order:

Na < F < Ne

e) Ionization energy decreases as we move down the group. Thus, the ionization energy follows in the given order:

Be > Mg > Ca