Explanation
Both ccp and hcp are highly efficient lattice; in terms of packing. The packing efficiency of both types of close packed structure is 74%, i.e. 74% of the space in hcp and ccp is filled. The hcp and ccp structure are equally efficient; in terms of packing.
The packing efficiency of simple cubic lattice is 52.4%. And the packing efficiency of body centered cubic lattice (bcc) is 68%.
NaCl is a kind of FCCunit cell*Anions are involved in closepacking. So Cl^-ions will be present at all the corners as well as at centre of each face Contribution of one anion at corner= 1/8 Total contribution = 1/8 × no. of corners = 1/8 × 8= 1 Contribution of one anion at face centre = ½ Total contribution = 1/2×no. Of faces = 1/2×6= 3 So, total number of anions =1+3 = 4* Cations move to the voids . So Na+ ions will be present in the octahedral voids ( they don't move to tetrahedral voids as they are larger in size than the tetrahedral voids). No. Of octahedral voids = no. Of constituent particles = 4So, we have total 4 Na + ions in a unit cell = 4 Na+ ions and 4 Cl- ions.
unit cell
*Anions are involved in closepacking. So Cl^-ions will be present at all the corners as well as at centre of each face
Contribution of one anion at corner= 1/8
Total contribution = 1/8 × no. of corners = 1/8 × 8= 1
Contribution of one anion at face centre = ½
Total contribution = 1/2×no. Of faces = 1/2×6= 3
So, total number of anions =1+3 = 4
* Cations move to the voids . So Na+ ions will be present in the octahedral voids ( they don't move to tetrahedral voids as they are larger in size than the tetrahedral voids).
No. Of octahedral voids = no. Of constituent particles = 4
So, we have total 4 Na + ions in a unit cell
= 4 Na+ ions and 4 Cl- ions.
Most crystals show good cleavage as their atoms, ions or molecule are arranged in planes which is due to flat crystal face.
In the close packing of atoms, the number of tetrahedral voids per atom is two and the number of octahedral voids per atom is one. These are applicable for cubic closed packing (CCP) and hexagonal closed packing (hcp).
Thus, option B is correct.
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