Account for the following:
(i) Schottky defects lower the density of related solids.
(ii) Conductivity of silicon increases on doping it with phosphorus.

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Solution

(i) In Schottky defect, equal number of cations and anions are missing from their lattice sites. As a result number of ions decreases and thus mass decreases but volume remains same. This cause decrease in density $(d e n s i t y = \frac{m a s s}{v o l u m e})$ of the solids having Schottky defect.
(ii) Phosphorus is a group 15 element and has five electrons in its valence shell. Upon doping silicon with phosphorus, after forming four bonds with neighbouring silicon atoms, the fifth extra electron is free and gets delocalised which increases the conductivity of silicon.

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Q. Account for the following:
(i) Conductivity of silicon increases on doping it with phosphorus

(ii) Schottky defects lower the density of related solids

Give reasons :A) Frenkel defects are not found in alkly metal halides.

B) schottky deffect lower the density of related solides

Q. Match the defects given in column I with statements given in column II and mark the appropriate choice.

	Column I		Column II
(A)	Simple vacancy defect	(i)	Shown by non-ionic solids and increases the density of the solid.
(B)	Simple interstitial defect	(ii)	Shown by ionic solution and decreases the density of the solid
(C)	Frenkel defect	(iii)	Shown by non-ionic solids and decreases the density of the solid
(D)	Schottky defect	(iv)	Shown by ionic solids and density of the solid remains the same

Match the defects given in Column I with the statements in given Column II.

$\begin{matrix} C o l u m n I & C o l u m n I I A . & s i m p l e v a c a n c y d e f e c t & 1. S h o w n b y n o n - i o n i c s o l i d s a n d i n c r e a s e s d e n s i t y o f t h e s o l i d B . & S i m p l e i n t e r s t i t i a l d e f e c t & 2. S h o w n b y i o n i c s o l i d s a n d d e c r e a s e s d e n s i t y o f t h e s o l i d c . & F r e n k e l d e f e c t & 3. S h o w n b y n o n - i o n i c s o l i d s a n d d e n s i t y o f t h e s o l i d d e c r e a s e s D . & S c h o t t k y d e f e c t & 4. S h o w n b y i o n i c s o l i d s a n d d e n s i t y o f t h e s o l i d r e m a i n s t h e s a m e \end{matrix}$

Q. Calcium crystallises in face-centred cubic unit cell with

a = 0.556 n m

. Calculate density if:
(i) it contained

0.1

% Frenkel defect.
(ii) it contained

0.1

% Schottky defect.

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Account for the following: (i) Schottky defects lower the density of related solids. (ii) Conductivity of silicon increases on doping it with phosphorus.

Account for the following:
(i) Schottky defects lower the density of related solids.
(ii) Conductivity of silicon increases on doping it with phosphorus.