Close Packed Structures In solids, the constituent particles are close-packed, leaving the minimum vacant space. (a) Close Packing in One Dimension In close packing one dimension, spheres are arranged in a row such that adjacent atoms are in contact with each other. (b) Close packing in Two Dimensions In two-dimensional close packing, a row of closed packed spheres is stacked to obtain a two-dimensional pattern. This stacking is done in two ways: Square close packing and Hexagonal close packing Square close packing or AAA... Type arrangement - The spheres of second row are exactly above those of the first row. The second row is exactly same as the first one. If we label the first row as A, the second row is also A. Similarly, we may place more rows to get AAA… type arrangement. In this arrangement, the spheres are found to form squares. This type of packing is known as square close packing in two dimensions. Hexagonal close-packing or ABABA… Type arrangement - The spheres in the se