Which type of packing is represented by a unit cell in which each sphere is surrounded by six others in the same plane, and layers are stacked directly on top of each other?

• A. Simple cubic packing
• B. Body-centered cubic packing
• C. Face-centered cubic packing
• D. Hexagonal close-packed

Answer: (A)

Verified step by step guidance

1. Understand the coordination number, which is the number of nearest neighbors surrounding each sphere in the packing. Here, each sphere is surrounded by six others in the same plane.
2. Recognize that in simple cubic packing, each sphere touches six neighbors: four in the same layer (forming a square arrangement) and one above and one below, making a total coordination number of 6.
3. Note that the layers in simple cubic packing are stacked directly on top of each other, meaning the spheres in one layer align exactly with those in the layers above and below.
4. Compare this with other packings: body-centered cubic has a coordination number of 8, face-centered cubic and hexagonal close-packed have coordination numbers of 12, and their layers are not stacked directly on top of each other but are offset.
5. Conclude that the description matches simple cubic packing because of the coordination number of 6 and the direct stacking of layers.