LEWIS ACID BASE THEORY

Nadia and Vito

acidA substance which produces hydrogen ions,

H+, when it is dissolved in water.

Properties: • Acids have a sour taste.• Acids dissolve in water to form solutions which conduct

electricity. • Acids turn blue litmus paper red. • Acids react with reactive metals to form hydrogen and a

salt.• Acids react with carbonates to form a salt, carbon dioxide

and water. • Acids react with bases to produce a salt and water only.

base - alkaliBase is any metal oxide or hydroxide – it

contains either oxide ions, O2-, or hydroxide ions, OH-.

Alkali is a base that is soluble in water.

Properties:• Alkalis have a bitter taste and soapy feel. • Alkalis turn red litmus paper blue. • Alkalis produce hydroxide ions when dissolved in water. • All alkalis can react with acids to form a salt and water only

the lewis acid base theory• The Lewis Acid Base Theory suggests

an acid as the reactant that receives an electron pair from another reactant in a chemical reaction, and a base as the reactant that that donates an electron pair to another reactant.

• In a Lewis Acid-Base reaction, the base donates an electron pair, forming a coordinate covalent bond joining the two species together into the reaction product.

lewis acids and bases• A Lewis acid is a any substance that can

accept a pair of nonbonding electrons. Lewis acids are electron-pair acceptors.– All cations.– All molecules possessing an atom with incomplete octet.

• A Lewis base is any substance that can donate a pair of nonbonding electrons. Lewis bases are electron-pair donors. – All anions.– All molecules having lone-pairs of electrons.

lewis acid base reaction• From the definition of acid and base suggested by Lewis,

we can write acid-base reactions like this:

• Characteristics of these reactions:– They are charge balanced – the total charge of all species is the same on both sides.– The product is sometimes described as a Lewis “complex”.– Red arrows are used to show the how the bond between the acid and base is formed.

• The tail sits on a pair of electrons.• The head sits on points to where these electrons will be in the product.

homo-lumo• In modern theoretical language:– the Lewis base’s filled orbital is the highest

occupied molecular orbit – or HOMO.– The Lewis acid’s empty orbital is the lowest

unoccupied molecular orbit – or LUMO.

• We refer to the interaction as the “filled-empty” interaction or the “HOMO-LUMO” interaction.

example of reactionBF3 + NH3 ?

Consider the molecules BF3 and NH3. If we determine the Lewis structure of BF3 and NH3, we find that B is octet

deficient and can accept a lone pair. While N is capable of donating a lone pair. N donates a pair of electrons to B,

creating a coordinate covalent bond between them.

Acid BaseLewis Complex

• Predict whether the following ions or molecules can act as either a Lewis acid or a Lewis base.– Ag+

–NH3

references

• http://www.nyu.edu/classes/tuckerman/honors.chem/lectures/lecture_21/node4.html

• http://chemistry.umeche.maine.edu/CHY251/Lewis.html

• http://facultyfp.salisbury.edu/dfrieck/htdocs/212/rev/acidbase/lewis.htm

• http://www.wou.edu/las/physci/ch412/ligand.htm• https://chemistry.twu.edu/tutorial/

AcidBaseConceptsSum.html