CATION ANION FORMATION HOW ION ARE FORMED? EXOTHERMIC AND EDNOTHERMIC REACTION POLY ATOMIC ION

2. Prof. Sohaib Hasnain
Punjab Group of Colleges, Faisalabad
CHEMISTRY

4. WHAT IS ION?
SPECIE CARRYING EITHER
POSITIVE OR NEGITIVE CHARGE

5. IONS ARE FORMED BY THE
ADDITION OR REMOVAL OF
ELECTRON

6. TYPES OF IONS
 POSITIVE ION
 NEGITIVE ION

7. POSTIVE ION
POSITIVE ION IS FOMED BY THE REMOVAL OF ELECTRON
For Example

8. POSITIVE ION/ CATION
 They are also called cations
 They have positive charge
 They are formed by the removal of electron
 They may carry +1, +2, +3 charge depending upon the number of
electrons lost by the atom

9. Cation Formation Is An Endothermic
Reaction
 ENDOTHERMIC REACTION
The reactions in which energy is required are called endothermic
reactions.
 Energy is required to remove the electron from the atom because
electron is bonded to nucleus of an atom
ΔH= +496 KJ/mol
 Hence, cation formation is an endothermic reaction

10. Cation formation is an
Oxidation Reaction
Oxidation means removal of electron
Hence, it is called oxidation reaction

12. Why Cation is smaller than parent atom?
 A neutral atom has same number of protons and electrons
 Cation is formed by the removal of electron, number of electrons
decreases
 Number of proton remains same
 Nuclear charge increases on the valance shell electrons
 Hence, When we remove the electron from the atom, size of atom
decreases

13. 186pm 95pm

14. NEGITIVE ION
NEGITIVE ION IS FOMED BY THE ADDITION OF ELECTRON
For Example

15. NEGITIVE ION/ ANION
 They are also called Anions
 They have negative charge
 They are formed by the addition of electron
 They may carry -1, -2, -3 charge depending upon the number of
electrons gain by the atom

16. Anion Formation Is An Exothermic
Reaction
 EXOTHERMIC REACTION
The reactions in which energy is released are called exothermic
reactions.
 Energy is released when we add the electron to the atom because
electron is attracted to nucleus of an atom
ΔH= -349 KJ/mol
 Hence, anion formation is an exothermic reaction

17. Anion formation is an
Reduction Reaction
Redution means addition of electron
Hence, it is called reduction reaction

18. Why Anion is larger than parent atom?
 A neutral atom has same number of protons and electrons
 Anion is formed by the addition of electron, number of electrons
increases
 Number of proton remains same
 Nuclear charge decreases on the valance shell electrons
 Hence, When we add the electron to the atom, size of atom increases

19. 99pm 181pm

20. Formation of Di-negative ion is an
endothermic process.
• A uni-negative atom, already has one excess electron in its valence
shell, which is providing it its negetive charge
• Now when, another electron is added to the valence shell, it faces
repulsion from this already present electron, and thus, some energy is
required to add this electron

21. WHY CATION IS SMALLER
THAN ANION?
OR
WHY ANION IS LARGER
THAN CATION?

22. • Cation is formed by the removal of electron, while anion is formed by
the addition of electron
• Removal of electron from the atom decreases the size because the
nuclear charge increases
186pm 95pm
• Addition of electron to atom increases size because the nuclear charge
decreases
99pm 181pm
Hence, cation is smaller than anion

23. Difference b/w metals and non-metals
METALS
• These form cation
• These lose their electron easily
• These have low ionization energy
NON-METALS
• These form anion
• These gain electron
• These have high electron affinity

24. What are polyatomic ions ?
 These are the positive or negative ions which consist of group of
atoms
 Positive polyatomic ions
NH+
4 and carbocations in organic chemistry
 Negative polyatomic ions
OH-, C2O-2
3, SO4
-2 ,Cr2O7
-2