Question

Define Ionization energy or Ionization potential of an atom.

Answer 1

- Hint: Ionization energy is the energy required to remove the electron from the outermost shell of an isolated gaseous atom. The more tightly this outermost electron is bound to the nucleus, more energy is required to remove it.

Complete step-by-step solution
Orbiting electrons in an atom are attracted to its nucleus. Their attraction force can be described by the electrostatic force as;
$\overrightarrow{F}={\displaystyle \frac{kZe.e}{r^2}}$
Where,
Ze is the charge on the nucleus, nucleus is positively charged, and Z is the atomic number.
e is the negative charge on the electron
r is the radius or the orbit in which the electron is orbiting.
To remove this outermost orbiting electron, we need to work against the electrostatic attractive force exerted on the electron by the nucleus. So, we need energy in this process and this energy is called ionization energy of an atom.
Ionization energy of an atom depends on the chemical properties of an atom. In some atoms outermost electrons are more tightly bound than other atoms, so their ionization energy will be higher than others.
Ionization energies can further be described as follows;
(1) First ionization energy- When the outermost electron is removed from a neutral atom, then required energy is called “First ionization energy”. After removal of the first electron this atom gets converted into a uni-positive ion, because after removal of the electron atom has net +1 charge on it.
$A\to A^{+}+e^{-}$
(2) Second ionization energy- When the outermost electron is removed from a uni-positive atom, required energy is called “Second ionization energy”. Now an atom is left with +2 charge on it, and is called bi-positive ion.
$A\to A^{2+}+e^{-}$
(3) Third ionization energy- When the outermost electron is removed from a bi-positive ion, required energy is called “Third ionization energy”. Now the ion will have +3 chare on it, and will be called a tri-positive ion.
$A^{2+}\to A^{3+}+e^{-}$

Additional information:
Comparison between first, second, and third ionization energy-
Outermost electron in the uni-positive ion is more tightly bound to the nucleus, because of reduced distance from the nucleus, than the neutral atom. So, more energy will be required in case of uni-positive ions to further ionize it. Thus, order of ionization energy is;
Tri-positive ion > Bi-positive ion > uni-positive ion > neutral atom.

Note: (1) Ionization energy decreases in a group as atomic number increases. As atomic number increases, the size of an atom also increases, so the outermost electron’s distance from the nucleus also increases. Thus, the outermost electron will be loosely bound to the nucleus, and less ionization energy will be required.
Ionization energy order- Li > Na > K > Rb > Cs
(2) Ionization energy increases along a period with increase in atomic number. As we move along a period in the periodic table, size of an atom decreases due to increase in nucleus attractive force. Thus, more energy will be required to remove the outermost electron.
Ionization energy order- Li < Be < B < C < N < O < F < Ne
(3) Ionization energy of inert gases will be maximum. Because they have the most stable electronic configuration, which makes them most stable.
Ionization energies are of great use in chemistry. It gives a rough estimate about the atom's characteristics. If the ionization energy of an atom is less, it will be more reactive