The geometry and symmetry of the elements .
     By definition elements are composed of only one type of atom species.  Therefore .
their atomic structures lend themselves readily to being modeled as packings of .
equal radius spheres.  The majority of elements exhibit either FCC, HCP, or BCC .
packing of their atoms. .
.

H

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

He

Li

Be

 

 

 

 

 

 

 

 

 

 

B

C

N

O

F

Ne

Na

Mg

 

 

 

 

 

 

 

 

 

 

Al

Si

P

S

Cl

Ar

K

Ca

Sc

Ti

V

Cr

Mn

Fe

Co

Ni

Cu

Zn

Ga

Ge

As

Se

Br

Kr

Rb

Sr

Y

Zr

Nb

Mo

Tc

Ru

Rh

Pd

Ag

Cd

In

Sn

Sb

Te

I

Xe

Cs

Ba

La

Hf

Ta

W

Re

Os

Ir

Pt

Au

Hg

Tl

Pb

Bi

Po

At

Rn

Fr

Ra

Ac

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Lanthanides

Ce

Pr

Nd

Pm

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

 

Actinides

Th

Pa

U

Np

Pu

Am

Cm

Bk

Cf

Es

Fm

Md

No

Lr

 

.

.

 

 

 

 

 

FCC

HCP

BCC

CP

HP

Diamond

.

 

 

 

 

 

.

Table 2 -   Periodic table of the elements showing atomic packing arrangement

.
              (all elements, including gases, considered to be in their solid state)
 
     The BCC structure is favored by elements with low numbers of valence electrons.
Elements with larger numbers of valence electrons favor the closer packed FCC and
HCP structures.
 
Face centered cubic (FCC) structure elements
Ac, Ag, Al, Ar, Au, Ce, Cu, In, Ir, Kr, Ne, Ni, Pb, Pb, Pd, Pt, Rh, Th, Xe
 
Crystal lattice
 

fcc.gif

   
Figure 45 -   FCC elements crystal lattice
 
                         click image to enlarge
.      
     The above image shows the ABC staggered arrangement of the successive layers
of atoms characteristic of the FCC lattice.  The view is taken looking down on the
(111) plane which is comprised of atoms in the triangulated closest packed array.  In
the process of building this model of the lattice the structural stability afforded by the
omni-triangulation of 3D space can be appreciated first hand.

Back to Knowhere

page 30 of lesson

Page  31 -  Structure matters - FCC elements

page 32 of lesson

 

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