Final answer:
In metallic crystals, the most tightly packed structures are the cubic closest packing (CCP) and hexagonal closest packing (HCP), which allow for the maximum interaction between atoms. Looser structures like the simple cubic and body-centered cubic structures are not as efficiently packed. X-ray diffraction is a technique used to determine the specific packing arrangement within a crystalline solid.
Step-by-step explanation:
Crystal Structures: Tightly Packed vs. Loosely Packed
When discussing crystal structures in metals, we often refer to how tightly the atoms are packed together. Closest packing is considered the most efficient arrangement, leading to the most energetically stable structures due to maximized interaction between atoms. This intricate structure not only minimizes the empty space between atoms but also maximizes the overall attractions, contributing to the physical properties of the metal. There are two main types of closest packed structures in metallic crystals:
- Cubic closest packing (CCP): Here, the third layer of atoms is distinct from the first two layers, leading to a stacking pattern of ABCABCABC... Metals such as Ag, Al, Ca, Cu, Ni, Pb, and Pt crystallize in a CCP structure.
- Hexagonal closest packing (HCP): In this structure, the third layer of atoms is directly above the first layer, creating an ABABAB... stacking sequence. Metals including Cd, Co, Li, Mg, Na, and Zn adopt an HCP structure.
Others, like simple cubic structures and body-centered cubic structures, are not as tightly packed. These structures have more space between the atoms and, consequently, allow for different properties.
Experimental Determination of Crystal Structures
The types of packing in crystalline solids can be determined by techniques like X-ray diffraction, which provides insights into the size and shape of a unit cell and the contents within it. This experimental method helps differentiate between tightly packed structures and those with a looser arrangement of atoms.