Learning Objective: To learn about the requirements for an ionic bond formation from the perspective of the electronegativity difference between atoms, and their ease of formation of ions.
Skill Level – Intermediate
Prerequisites:
Related –
Effective Nuclear Charge
Shielding Effect
Periodic Table Trends – Ionization Enthalpy, and Electron - Affinity Enthalpy
Ionic and Covalent Character according to Fajan’s Rule
Chapter: Bonding in Atoms
Author's Note: In the previous section, we briefly saw how ions form ionic bonds and how ionic compounds release lattice energy.
In this section, we will see, using the periodic table, which ionic combination can form an ionic bond based on their electronegativity differences. We already know atoms form ions; however, the ease with which they do depends on the ionization enthalpy value for the cations and the electron affinity values for the anions. We learn about the strength of ionic bonds based on size, charge, and lattice enthalpy values, so that just by comparing two ionic compounds, we will know for sure which combination would be predominantly ionic and stronger. Also, an ion combination that results in a higher ionic or covalent character.
Requirements for Ionic Bonding
An easy way to identify which atoms are likely to participate in ionic bonding is by calculating their electronegativity difference (∆EN). The difference in their electronegativity must be higher than 1.7. That way, the bond formed is predominantly ionic. For example, NaCl has an electronegativity difference of 2.1.
Therefore, the interacting atoms of the elements must preferably come from.....
..
In addition to the electronegativity difference, the other essential factors to be considered affecting the bond formation are the ionization enthalpy of the cations and the electron-gain enthalpy of the anions.
Ease of Formation of the Cations
The loss of an electron from an atom to form a cation depends on the ionization enthalpy, that is, the energy required to dislodge an electron from a free neutral atom to form an ion.
Some atoms are more willing to lose...
The effect is highest for the elements...
The decrease in size is due to the increased nuclear...
But once the loosely held electrons ...
Ease of Formation of the Anions
The ability of atoms to accept electrons and form anions is measured by electron affinity enthalpy values in kJ/mol.
Affinity for an electron increases for ...
For example, the size of the Cl- ion is 0.181 nm....
The electron affinity trend reverses as ....
Based on purity of ionic character, we see that, ionic bonds formed with the anions....
Summary Based on the Ionic Bond Strength –
The strength of an ionic bond is measured by the lattice energy of the resulting ionic compound, which is the energy released when gaseous ions form a solid crystal lattice.
Higher the lattice energy...
Key factors determining...
This is why compounds like MgO (magnesium oxide) have extremely high....
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