Close Packing

Q.

A crystal is made up of metal iron ${\mathrm{M}}_1$ and ${\mathrm{M}}_2$ and oxide ions. Oxide ions form a $\mathrm{ccp}$ lattice structure. The cation ‘${\mathrm{M}}_1$ occupies 50% of octahedral voids and the cation ${\mathrm{M}}_2$occupies 12.5% of tetrahedral voids of oxide lattice. The oxidation number of ${\mathrm{M}}_1$ and ${\mathrm{M}}_2$ are, respectively:

1. $+2,+4$

2. $+3,+2$

3. $+4,+2$

4. $+1,+3$

Q. Atom $X$ occupies the fcc lattice sites as well as alternate tetrahedral voids of the same lattice. The packing efficiency (in$\%$) of the resultant solid is closest to

1. $25$
2. $55$
3. $35$
4. $75$

Q.

In a binary compound, atoms of element A form the hcp structure and those of element M occupy 2/3 of the tetrahedral voids of the hcp structure. The formula of the binary compound is:

1. M₂A₃

2. MA₃

3. M₄A

4. M₄A₃

Q.

How many unit cells are present in a cubic -shaped ideal crystal of NaCl of mass 1.00 g [Atomic masses: Na= 23, Cl = 35.5]

1. $2.57\times {10}^{21}$ unit cells

2. $5.14\times {10}^{21}$ unit cells

3. $1.28\times {10}^{21}$ unit cells

4. $1.71\times {10}^{21}$ unit cells

Q. Copper crystallises in F.C.C. with a unit cell length of 361 pm. What is the radius of copper atom?

1. 108 pm
2. 127 pm
3. 181 pm
4. 157 pm

Q. In a compound, atoms of element Y form ccp lattice and those of element X occupy $\frac{2}{3}$ rd tetrahedral voids. The formula of the compound will be:

1. $X_2{Y}_3$
2. $X_3{Y}_4$
3. $X_4{Y}_3$
4. $X_{2}Y$

Q.

A binary solid (A⁺B^-) has a zinc blend structure with B^- ion constituting the lattice and A⁺ion occupying the 25% tetrahedral voids. The formula of solid is _________

Q.

The Coordination number of ccp is ____?

Q. Lthium metal crystallises in a body centred cubic crystal. If the length of the side of the unit cell of lithium is $351pm$, the atomic radius of the lithium will be :-
($\sqrt{3}=1.732$)

1. $240.8\text{pm}$
2. $149.17\text{pm}$
3. $75.5\text{pm}$
4. $300.5\text{pm}$

Q.

The number of atoms in each unit cell in ccp structure is:

1. 4 atoms

2. 5 atoms

3. 6 atoms

4. 8 atoms

Q.

The number of atoms in the hcp unit cell is

1. $4$

2. $6$

3. $12$

4. $13$

Q. A solid has a BCC structure. If the distance of closest approach between the two atoms is $1.73\stackrel{\circ }{A}$. The edge length of the cell is-
($\sqrt{3}=1.73$)

1. $200pm$
2. $\frac{\sqrt{3}}{\sqrt{2}}pm$
3. $142.2pm$
4. $\sqrt{2}pm$

Q.

In the cubic close packing, the unit cell has

(a) 4 tetrahedral voids each of which is shared by four adjacent unit cell

(b) 4 tetrahedral voids within the unit cell

(c) 8 tetrahedral voids each of which is shared by four adjacent unit cells

(d) 8 tetrahedral voids within the unit cells

Q.

Which of the following lattices has the highest packing efficiency (i) simple cubic (ii) body-centred cubic and (iii) hexagonal close-packed lattice?

Q. In a face centerd lattice of $X$ and $Y,X$ atoms are present at the corners while $Y$ atoms are at face centers. Then, the formula of the compound would be if one of the $X$ atoms is missing from a corner in each unit cell:

1. $X_7{Y}_{24}$
2. $X_{24}{Y}_7$
3. $X{Y}_{24}$
4. $X_{24}Y$

Q. The silver metal crystallizes with a face-centred cubic lattice. The edge length of the unit cell is $4.08\stackrel{o}{A}$. Calculate the percentage of empty space in the FCC structure?

1. $52\%$
2. $74\%$
3. $26\%$
4. $31\%$

Q. First three nearest neighbour distances for primitive cubic unit cell will be, respectively:
(Here, edge length of unit cell $=l$ )

1. $l,\sqrt{2}l,\sqrt{3}l$
2. $\sqrt{3}l,\sqrt{2}l,l$
3. $l,\sqrt{2}l,2l$
4. $l,\sqrt{2}l,l$

Q. The correct statement(s) for cubic close packed (ccp) three dimensional structure is/are:

1. The number of the nearest neighbours for an atom present in the topmost layer is 12.
   
2. The efficiency of atom packing is 74%.
3. The number of octahedral and tetrahedral voids per atom are 1 and 2, respectively.
4. The unit cell edge length is $2\sqrt{2}$ times the radius of the atom.

Q. A. Binary solid A plus B minus has a structure withB minus ions constituting the lattice and A plus occupied 25% tetrahedral holes formula of solid

A2B
AB
AB2
AB4

Q. In an arrangement of type ABABA ....., identical atoms of first layer A and third layer A are joined by a line passing through their centres.
Choose the correct statement from the following.

1. No void is found on the line
2. Only tetrahedral voids are found on the line
3. Only octahedral voids are found on the line
4. Equal number of tetrahedral and octahedral voids are found on the line

Q. Gold crystallizes in the FCC lattice. Calculate the approximate number of the unit cells in 2 mg of gold (atomic mass of gold is 197 u)

Q. The ABAB.. type packing and ABCABC.. type packing are respectively called as:

1. hexagonal close packing (hcp) and cubic close packing (ccp)
2. cubic colsed packing (ccp) and hexagonal colsed pacing (hcp)
3. body centered cubic(bcc) close packing and hexagonal close packing (hcp)
4. hexgonal closed packing (hcp) and body centred cubic (bcc) close packing

Q. The coordination number in 3-D BCC close packing structure is

1. 6
2. 4
3. 8
4. 2

Q. Choose the correct statement regarding cubic close packing.

1. Fourth layer is not identical to the first layer
2. Cubic close packing gives fcc structure
3. Cubic close packing gives bcc structure
4. Fourth layer is identical to the second layer

Q.

Write the chemical formula of the compound calcium bicarbonate in a step-by-step manner.

Q.

Which of the following is a covalent crystal?

1. Quartz

2. Rock salt

3. Ice

4. Dry ice

Q.

The packing efficiency of the face-centered cubic (fcc), body-centered cubic (bcc), and simple primitive cubic (pc) lattices follows the order:

1. fcc > bcc > pc

2. bcc > fcc > pc

3. pc < bcc < fcc

4. bcc < pc < fcc

Q.

If 'Z' is the number of atoms in the unit cell that represents the closest

packing sequence the number of tetrahedral voids in

the unit cell is equal to

[AIIMS 2005]

1. Z

2. 2Z

3. Z/2

4. Z/4

Q.

What is the coordination number in a square close-packed structure in two dimensions?

(a) 2 (b) 3 (c) 4 (d) 6

Q.

Which is more ionic NaCl or MgO? and Why?