Electronegativity difference is directly proportional to acidic strength. But ionic bonds are stronger than covalent bonds, making it harder for compounds having high electronegativity difference to donate proton. Then how is this possible ? Explain in detail.
Dear Student,
This concept can explained by stability of anion. When any acid loses proton, it becomes a conjugate base, which is an anion. Suppose we talk about water molecule. When water loses a proton, it becomes OH- ion, which is a conjugate base. Lets compare water with NH3 and CH4. The central atom has different electronegativities in all these compounds. The central atoms are O, N and C. The anions formed by losing proton are OH-, NH2- and CH3-. When we compare the stability of these anions, we need to compare the basisities of these anions. All these anions have same H atoms, only difference is the electronegativity of the central atom. As we move from C to O, the electronegativity increases. Thus, O will be most electronegative and would not like to share its pait of electrons, which makes it weaker base. But on the other hand, C is least electronegative, so it would easily share its pair of electrons making is stronger base. The OH- is weaker conjugate base, which means water is stronger acid. Thus order of acidity becomes, CH4 < NH3 < H2O.
I hope it is clear.
Regards
This concept can explained by stability of anion. When any acid loses proton, it becomes a conjugate base, which is an anion. Suppose we talk about water molecule. When water loses a proton, it becomes OH- ion, which is a conjugate base. Lets compare water with NH3 and CH4. The central atom has different electronegativities in all these compounds. The central atoms are O, N and C. The anions formed by losing proton are OH-, NH2- and CH3-. When we compare the stability of these anions, we need to compare the basisities of these anions. All these anions have same H atoms, only difference is the electronegativity of the central atom. As we move from C to O, the electronegativity increases. Thus, O will be most electronegative and would not like to share its pait of electrons, which makes it weaker base. But on the other hand, C is least electronegative, so it would easily share its pair of electrons making is stronger base. The OH- is weaker conjugate base, which means water is stronger acid. Thus order of acidity becomes, CH4 < NH3 < H2O.
I hope it is clear.
Regards