IB Chemistry SL Reactivity 3.4.6 Lewis Acid–Base Theory

Practise classifying Lewis acids as electron-pair acceptors and Lewis bases as electron-pair donors. Apply the definition to nucleophiles, electrophiles, catalysts and unfamiliar…

Exam points

classify the electron-pair donor as a Lewis base and the acceptor as a Lewis acid
identify the specific lone pair and electron-deficient atom involved in the interaction
connect nucleophiles with Lewis bases and electrophiles with Lewis acids in context

[Maximum number: 4]

The element boron has two naturally occurring isotopes, ${ }^{10} \mathrm{~B}$ and ${ }^{11} \mathrm{~B}$ .

(a)

Define an acid according to the Lewis theory.

[ 1 ]

(b)

State and explain the acid-base character of $\mathrm{NH}_{3}$ and $\mathrm{BF}_{3}$ according to the Lewis theory.

[ 3 ]

$N H_{3}$ : Lewis base;
$B F_{3}$ : Lewis acid;
$\mathrm{NH}_{3}$ has non-bonding/lone pair of electrons and $\mathrm{BF}_{3}$ has only 3 pairs of electrons around B / incomplete octet;

Reference to outer electrons of N and B is needed for the mark.

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3.4.6—Lewis acid-base theory question 1

Question (a)

Question (b)