LEWIS ACID-BASE CONCEPT:

According to Lewis acid base theory- acids are electron pair accepter (electron deficient) and bases are electron pair donor and the combination of Lewis acid and Lewis base occur through coordinate bond formation.
For example

Others examples of Lewis acid-base neutralization.

Lewis acids:

(1) Cations are act as Lewis acids example, H⁺ , Ag⁺ , Cu⁺² , Na⁺ , Fe⁺² , Hg⁺²  etc.
(2) Electron deficient compounds are act as Lewis acids for examples BF₃ ,ACl₃ ,BCl₃ ,FeCl₃ etc 
(3) The compounds  which central atom with available vacant d-orbital  can add additional pairs of electrons even though it already has an octet or more of electrons act as Lewis acids for examples SiCl₄,PCl₅, SOF₄, SbCl₃, SbF₅ ,SnCl₄, IF₇, SF₄ etc 
(4) Compounds containing multiple bonds for example CO₂ , SO₂, SO₃ ,CS₂ etc.

Lewis bases:

(1) Anions are act as Lewis base H^- ,CH₃^- ,NH^2- , OH^- , X^- etc. but all the anions are not Lewis base for example (PCl₅)^- 
(2) The Neutral molecules having lone pairs of electrons act as Lewis base for examples NH₃ ,R-NH₂, R-NH-R, R₃-N, H₂O , R-OH ,R-O-R , PH₃, R-PH₂ , R₂PH ,R₃P , H₂S , R-SH , R-S-R etc
(3) Compounds with non polar multiples bond  are also act as Lewis base, example Alkenes(C₂H₄) , Alkynes(C₂H₂ ) Dienes, polyenes, benzene, Polynuclear homoaromatic compounds. (Ligand in coordination compounds)

Chemical Reactions according Lewis acid-base concept:

We can now write equations for many reactions that involve a Lewis acid reacting with a Lewis base. The following are a few examples:

Acid-base behavior according to the Lewis theory has many of the same aspects as does acid-base theory according to the Brønsted–Lowry theory.

(1)There is no acid without a base. An electron pair must be donated to one species (the acid) by another (the base).

(2) An acid (or base) reacts to displace a weaker acid (or base) from a compound.

(3)The interaction of a Lewis acid with a Lewis base is a type of neutralization reaction because the acidic and basic characters of the reactants are removed.

An acid-base reaction takes place readily between BF₃ and NH₃ ,

                                         BF₃  +NH₃ → H₃N:BF₃

However, when the product of this reaction is brought into contact with BCl₃, a reaction takes place:

                                  H₃N:BF₃ +BCl₃ → H₃N:BCl₃  + BF₃

In this reaction, a Lewis acid, BF₃ , has been replaced by essentially a stronger one BCl₃ .  And replacement of Lewis  acid by other Lewis acid follow Second order Nucleophilic substitution (S_N²).

Merits of Lewis concept:
(1) The acid/base nature of substance may also defined without any solvent.
(2) It is highly useful to explain coordination compounds in which central metal atom into behave as Lewis acid and ligands behave as Lewis base.
(3) The acid having greater tendency to accept lone pair bare stronger acid and base have greater tendency to donate lone pair are stronger base.

Demerites of Lewis concept: 
(1) It is extremely generalized Concept , almost all the compounds either become acid or base  by this Concept.

Related Questions:

Why is BCl3 a strongerLewis acid than BF3 ?

Arrange the silicon halides into decreasing order of Lewis acids Character? SiF3, SiCl3, SiBr3, SiI3

Silianol (SiH3OH) is more acidic than methanol (CH3OH) why?

Why thionyl chloride behaves as Lewis acid as well as Lewis base?.

What is Lewis acid character order of Boron halides, arrange in increasing order?

What are the order of extent back bonding, Lewis acid character and nucleophilicity of (BF3, BCl3, BBr3, BI3)boron trihalides?

Arrange the silicon halides into decreasing order of Lewis acids Character? SiF4, SiCl4, SiBr4, SiI4

Levelling effect and relative strength of acids:

When strong acids like HClO₄, HCl, HBr, HI, HNO₃ etc are dissolved in water they are equally ionised (100%) it means they are equally strong in water this is called levelling effect of water.
Similarly for strong bases also , NaOH, KOH  Ca(OH)₂ etc are in water behave the same. hence relative strength of strong acids or base can not be compare in water .
(1) Water does no show levelling effect for weak acids or base because they are ionised upto different extent in water.
(2) All the acids are stronger than H₃O+ ion, consider as strong acids and weak than H₃O+ ion are consider as weak acids.
(3) All the bases stronger than OH^- are consider as strong base and weaker than OH^-, then they are consider  as weak base.

Definition: If more than one acids or bases are showing same acidic or basic strength in same solvent it is called labelling effect and the solvent is called labelling solvent for example:

(1) HClO₄ and HI equally dessociation in aqueous medium (99.99%)  it means they have equal strength.

(2) HCl, HNO₃  and H₂SO₄ are equally strong in water because their strength are “levelled” to solvent species H₃O+. only by putting them into a more acidic solvent do they weak acids. With determinate Pka values which differetiate their strengths. Thus in glacial ethanoic acid (acetic acid ) as solvent, the order of  acidic strength is as: H2SO₄ > HCl > HNO₃ .

(3) Similarly HF and HCl are equally dessociation in NaOH (100 %).
If their strength differ in same solvent ,it is called differential effect and the solvent is called differential solvent.

(4) For example HClO₄ dessociate 99.99 % in acetic acid while HI dissociate 99.8% in acetic acid, it means acidic strength of HClO₄ is more than HI in acetic acid.

(5) Many of inorganic oxoacid are strong acid (with more negative Pka value) inaqueous solution. But, as we have seen, use of solvent with a lower proton affinity than water like acetic acid, makes it possible to differentiate between the strength of these acids and measure Pka value.

H₂CO₃ < H₃PO₄ < H₂SO₄ < HClO₄ (Increasing acidic sterngth) these acidic strength can  also explain if the folmulae of the these oxy acids are written as base or OH formate or like that OC(OH)₂ < OP(OH)₃< O₂S(OH)₂< O₃Cl(OH) then it is clear that the acidic strength incrases as the number of oxygen atoms not involve in O-H bonding increases.

The reason behind levelling and diffential  effect is ability of solvent to donate or accept protons .
For acids, acidic solvents are differential and basic solvent are levelling.

Related Questions:

What are "pyro" oxy acids?

What are "Ortho" or "Meta" oxyacids?

What is Meta Boric Acids?

What are the structural difference between oxides ( P4O6 and P4O10) of phosphorous?

What are common structural features of oxides (P4O6 and P4O5) of phosphorous?

What is "calgon" ? Give structure and its uses?

Structure of Oxy acids of Phosphorous:

What is structure of (HPO3) metaphosphoric acid?

What is metaphophoric (HPO3)?