5.0 Ionization Potential

  Periodic Table

• The energy required to remove the most loosely bound electron from the outermost orbit of one mole of isolated gaseous atoms of an element, is called as ionization potential (IP). This ionization is an endoergic or energy-absorbing process.
• An electron cannot be removed directly from an atom in solid state. For this purpose, the solid state is converted to gaseous state and the energy required for this is called sublimation energy. $${A_{(g)}}\mathop \to \limits^{{1^{st}}IP} {A^{ + 1}}_{(g)}\mathop \to \limits^{{2^{nd}}IP} {A^{ + 2}}_{(g)}\mathop \to \limits^{{3^{rd}}IP} {A^{ + 3}}_{(g)}$$

• The energy required to remove one electron from a neutral gaseous atom to convert it to monopositive cation, is called first ionization potential ($1^{st}$ IP). The energy required to convert a mono-positive cation to a di-positive cation is called second ionization potential ($2^{nd}$ IP).
• ${1^{st}}$ IP < ${2^{nd}}$ IP < ${3^{rd}}$ IP, because as the first electron is ionized, the effective nuclear charge increases & the ionic size goes on decreasing. Thus the forces of attraction on valence shell electrons increases and hence the order.