Closest Packing of Spheres

Closest Packing of Spheres

• The arrangement of equal-sized atoms or ions that maximizes packing efficiency while minimizing empty space

• Produces the most stable crystal structures for many metals

CCP & HCP

Name the two types of closest-packed arrangements

Cubic Closest Packing

Full-form of CCP

Hexagonal Closest Packing

Full-form of HCP

Packing Efficiency

The percentage of a unit cell's volume that is occupied by atoms

Less empty space

A higher packing efficiency indicates what?

74%

Provide the packing efficiency of CCP and HCP

Close-Packed Layer

• A single layer of atoms arranged so that each atom touches six neighboring atoms

• Forms a two-dimensional hexagonal pattern

• Serves as the building block for CCP and HCP structures

Triangular Hole

• A triangular gap formed between three touching atoms in one layer

• Atoms in the next layer sit inside these holes

Second Layer (Layer B)

• The layer placed above Layer A

• Every atom sits in a triangular hole of Layer A

• Creates the first close-packed arrangement

ABABAB

Hexagonal Closest Packing (HCP) stacking sequence

ABAB Stacking Sequence

• The repeating layer arrangement in HCP

• Layer B sits in the triangular holes of Layer A

• The third layer returns directly above Layer A

12

Coordination number of Hexagonal Closest Packing (HCP) and CCP

Hexagonal Unit Cell

• The repeating unit used to describe HCP crystals

• Contains layers arranged in an ABAB pattern

Magnesium, Titanium, Zinc, Cobalt, and Cadmium

List all the Common HCP Metals

ABCABC

Cubic Closest Packing (CCP) stacking sequence

Third layer

Which layer in CCP occupies the new set of triangular holes?

Stacking Sequence

CCP emphasizes what?

Unit cell geometry

FCP emphasizes what?

Copper, Aluminum, Silver, Gold, and Nickel

Include all the CCP Metals