In hexagonal systems of crystals, a frequently encountered arragenement of atoms is…
Chemistry · JEE Advanced · NTA Exams — Solid State
In hexagonal systems of crystals, a frequently encountered arragenement of atoms is described as a hexagonal prism. Here the top and bottom of the cell are regular hexagons and three atoms are sandwiched in between them. A space-filling model of this structure, called hexagonal close-packed (HCP), is constituted of a sphere on a flat surface surrounded in the same plane by six identical spheres as closely as possible. Three spheres are then placed over the first layer so that they touch each other and represent the second layer. Each one of these three spheres touches three spheres of the bottom layer. Finally, the second layer is covered with a third layer that is identical to the bottom layer that is identical to the bottom layer in relative position. Assume radius of every sphere to be ‘r’. (2008)
The number of atoms on this HCP unit cell is :
- 4
- 6
- 12
- 17
Answer
(B) 6
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