Ionisation energy and its variation in periodic table ~ NEET chemistry

Ionisation energy :---

Ionisation energy is the amount of energy required to remove the most loosely bound electron of an isolated neutral gaseous atom or molecule.

For example:-- A is a atom, when we give energy to A atom loosely bound electron ots outermost shell.

A + energy = A+ + electron

:- ionisation energy is a endothermic process.

:- if outermost electron is closer to the nucleus of the atom, the ionisation energy is higher in amount

But is away from the nucleus, ionisation energy is less in amount.

:- the unit of ionisation energy kilojoule/mole , kilocalorie/mole , ev/atom

1 ev/atom = 96 kJ/mole

General trend in periodic table :---

Ionisation energy generally invreases from left to right acroos the period (Row)
Ionisation energy generally decreases from top to bottom in a group (column)

The first three ionisation energy are defined as follows:---

A +energy = A+ Elevtron (IE¹)

A+ = A²+ + electron (IE²)

A²+ = A³+ + elevtron (IE³)

Order of first three ionisation energy :--

IE¹<IE²<IE³

Note:---IE¹+IE²+IE³>0

Factors affecting ionisation energy :--@

Electronic configuration :--- stable configuration (s3, p3, p6, d5, d10, f7, f14) has more ionisation energy.

For example :---

Nitrogen = 1s2 2s2 2p3 ( half filled stable configuration)

Oxygen = 1s2 2s2 2p4 ( unstable configuration)

IE = N>O

2. Number of electronic shells:-- No of shells increases, it means outermost electron loosely bound with nucleus and remove easily. Therefore ionisation energy decreases.

3. Effective nuclear charge ( Zeffect) :---

If shielding and penetration effect are greater then attraction of nucleus on electron is less and they bind loose and remove easily. Therefore the Zeffect of the electron decreases and ionisation energy also decreases.

4. Heavier element have smaller atomic radii and higher ionisation energy (more than 70)

5.lanthanoid and actinoid contraction decreases ,the size of atom and Zeffect decreases . Therefore, the ionisation energy increases.

Variation in IE with exception :---

For s block elements :---

In case of s block - it contain all metals ( alkaline metal and alkaline earth metal). Metals has the charactrristics to loose electron easily. Therefore, s block elements has low IE.

Moving up to down in a group ionisation energy decreases due to the attraction of nucleus on electrons decreases.
Moving across the period IE invreases, increasing with Zeffect.

Ist group :-- H>Li>Na>K>Rb>Cs

IInd group :-Be>Mg>Ca>Sr>Ba

For p block :---

Same Variation as s block across the period or in a group

13th group:--B>Tl>Ga>Al>In

14th group :--C>Si>Ge>Pb>Sn

15th group :--N>P>As>Sb>Bi

16th group:--O>S>Se>Te>Po

17th group:--F>Cl>Br>I

18th group :--He>Ne>Ar>Kr>Xn

Variation across the period:--

2nd period:- Li<B<Be<C<O<N<F<Ne

3rd period:-Na<Al<Mg<Si<S<P<Cl<Ar

For d block elements :--

IE of the d block elements is larger than s block and smaller than the p block elements.

In 3d series, except Cr And Cu first IE involves removal from filled S orbital. Among them, IE of d block elements increases with the Increase in atomic number up to Fe.

In 3d series From Co to Ni IE decreases, but Cu to Zn IE invreases as a s block elements.
In 4d series elements from Nb have single electron in the s orbital. Hence, they show a gradual increase in IE with increasing atomic no.
Pd has completed d shell and no electron in s orbital. Pd shows the maximum IE because of lanthanoid contraction.
In 5d series all elements except Pt and Au have filled s orbital.
Elements from Hf to Re have same IE and after IE increases with the increase of no. Of shared d electron such that Ir and Au have max. IE.

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