Polymorf - Knowhwere- HP elements

Simple hexagonal (HP) structure elements

Am, Bk, C (graphite), Cf, Cm

Crystal lattice

The crystal lattice of HP elements can be modeled as shown previously for the HP

sphere packing where hexagonal prisms stack together in an eclipsed arrangement.

Graphite has a special type of HP structure where the layers of hexagonal prisms

stack together in a staggered formation, as shown in the following image. In this

arrangement the hexagonal rings of carbon atoms in adjacent vertical layers are

staggered relative to each other, but alternating layers eclipse each other.


		Figure 50 - Graphite lattice structure

		click image to enlarge

Polyhedral framework (graphite)



		Figure 51 - Polyhedral framework
		model of graphite
		( 40 T, 42 S, 106 pinges )
		click image to enlarge

.

The polyhedral framework demonstrates that the graphite structure can be viewed

as two interpenetrating lattices (pictured red and blue here) with each cell of each

lattice comprised of two hexagonal prisms stacked on top of each other. The carbon

atoms are located at the corner vertices of these elongated HP cells. Notice the

shorter bond length between atoms of adjacent layers that eclipse each other

compared to atoms of alternate layers that are eclipsed. One half of the bonds

between atoms in the different layers are these longer bonds. This causes weakness

in the bond strength between atoms of different layers compared to the bond strength

of atoms within the same layer. As a result the separate layers to tend to slip past

each other. This accounts for graphite's excellent lubricant properties and its softness

as a marker.

Cleavage (graphite)

(100) - perfect and easy - the result of the relatively weaker inter-layer bonds

Crystal habit (graphite)

tablets, scaly

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