1.0   Atomic Orbitals

      Atoms are composed of a nucleus and electrons that surround the
      nucleus. The electrons tend to stay in specific locations around
      the atom called Atomic Orbitals. An Atomic Orbital may contain
      at most two electrons.

1.1   Types of Atomic Orbitals

      The Atomic Orbitals included in most chemical bonding are the s,
      p, and d type. Each Atom has only one s type orbital. An s
      orbital can bond in any direction. Each Atom has three p type
      orbitals (Px,Py,Pz). In 3-dimensional space one p orbital
      is parallel to each of the 3 axis: X,Y,Z. The direction
      that a p orbital will bond is determined by the axis it is
      parallel with. Each Atom has five d type orbitals Dxy, Dyz,
      Dxz, Dxx-yy, and Dzz (CHEMICAL numbers these a,b,c,d,e).

1.2   Atomic Orbital Hybrids

      The s, p, and d Atomic Orbitals can be combined to form a
      veriety of hybrids such as sp, dsp, sp2, etc. The number of
      hybrids formed matches the number of Atomic Orbitals that
      combined to form the hybrid. The directional characteristics
      taken by a hybrid are determined by the directional tendancies
      of the Atomic Orbitals that are combined. However, bonding atoms
      will tend to spread out evenly in 3 dimensional space. The
      hybrids formed are numbered with the symbols ' ` ^ ~ + : in
      CHEMICAL.

      CHEMICAL includes some special versions of the sp2 and sp3
      hybrids to make ring structures easier to generate. The
      sp2_5 and the sp3_5 hybrids should be selected if a 5 atom
      ring is desired. The sp2 and sp3_6 hybrids should be
      selected if a six atom ring is desired.

2.0   Molecular Orbitals

      Atomic Orbitals from two atoms can combine to form Molecular
      Orbitals, the electrons shared (covalently) between the two
      Atoms. Molecular Orbitals replace the Atomic Orbitals. Molecular
      orbitals are either Bonding or Anti-Bonding. The Bonding
      Orbitals are lower energy and are more commonly used for
      bonding. Each Molecular Orbital can hold at most two electons.

2.1   Types of Molecular Orbitals

      There are only three types of Molecular orbitals: sigma, pi, and
      delta. Sigma orbitals are formed when the "ends" of Atomic
      Orbitals bond, and thus are free to rotate after bonding. Pi and
      delta Molecular Orbitals are by side by side bonding and thus
      are not free to rotate. (CHEMICAL Version 2.0 does not include
      delta bonds)

3.0   Bonding

      Atomic and Molecular orbitals have energy states associated with
      them. Bonding occures when a lower energy state occures by
      sharing electrons. No more than two electrons may occupy any
      orbital. When many possible bondings exist the lowest energy one
      will dominate and determine the 3 dimensional configuration.

3.1   Bonding Electrons

      Typically each atom donates an electron for bonding. Sometimes
      one atom will donate both electrons, this is called a Dative
      bond. Sometimes bonding can only occure by using the higher
      energy anti-bonding orbitals.

3.2   Bond Order

      The bond order is determined by the number of pairs of electrons
      in bonding orbitals minus the number of pairs of electrons in
      anti-bonding orbitals. The higher the bond order the stronger the
      bond.

4.0   Size of Atoms

      Atoms for higher numbered elements are generally larger. The
      size also varies with the type of hybrid and bonding. CHEMICAL
      has a built in table of atom sizes according to the orbital
      type and bond order. This information was taken from the Van
      Nostrand's Scientific Encyclopedia.

5.0   Ionic Bonding

      Some atoms have strong electrostatic charge and tend to bond to
      atoms of opposite charge by Ionic Bonding. CHEMICAL has a built
      in table of atoms with strong electrostatic charge to construct
      chemicals with Ionic Bonding. Negative ions are large because
      they hae gained an additional electron. Positive ions are small
      due to the loss of an electron.

6.0   Electronegativity

      The power of attraction that an atom shows for electrons is called
      electronegativity. Electronegativity is a measure of the attraction 
      of an atom for electrons in its outer shell. The EGA colors in 
      CHEMICAL are selected to correspond to the electronegativity: Red
      being low and blue being high.