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Packing Efficiency

Posted by RAHMA CAHYANINGRUM pada Maret 9, 2010

The packing efficiency is the fraction of the crystal (or unit cell) actually occupied by the atoms. It must always be less than 100% because it is impossible to pack spheres (atoms are usually spherical) without having some empty space between them.

P.E. = (volume of spheres within the unit cell) / (volume of cell)

A. Side by side structure

1. Simple cubic

Simple cubic (sc) is the simplest and often is observed for metals where too close packing encounters greater repulsion of cations. In the unit cell below, the atoms at the corners are cut because only a portion (in this case 1/8) belongs to that cell. The rest of the atom belongs to neighboring cells.

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Orbitals for selected molecules

Posted by RAHMA CAHYANINGRUM pada Maret 6, 2010

1. Saturated molecules

These are molecules in which all valence electrons are involved in the formation of single bonds. There are no non-bonded lone pairs. These molecules are generally less reactive than either electron-rich or electron-deficient species, with all occupied orbitals having relatively low energies.

a. Methane:

The valence molecular orbitals of methane are delocalized over the entire nuclear skeleton – that is, it is not easy to assign any one orbital to a particular C-H bond. It is possible to see how complex the orbital structure becomes with the increase in energy. Methane has four valence molecular orbitals (bonding), consisting of one orbital with one nodal plane (lowest occupied) and three degenerate (equal energy) orbitals that do have a nodal plane.
For the energy diagram and pictorial view of the orbitals – please see below:

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The orbitals of some molecules

Posted by RAHMA CAHYANINGRUM pada Maret 6, 2010

The H2 molecule has two valence electrons.

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Diagram Orbital Molekul NH3

Posted by RAHMA CAHYANINGRUM pada Maret 6, 2010

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Orbital Molekul HF dan KF

Posted by RAHMA CAHYANINGRUM pada Maret 6, 2010

Diagram Orbital molekul HF

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