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Encyclopedia of Physical Science and Technology EN011H-551 July 25, 2001 18:33

Periodic Table (Chemistry)

N. D. Epiotis
D. K. Henze
University of Washington

I. Development of the Periodic System
II. Features of the Modern Periodic Table
III. Atomic Structure and Elementary Periodicity
IV. Tabular Trends
V. The New Valence Bond Interpretation of
Chemistry
VI. The Colored Periodic Table
VII. The Hard/Soft Acid-Base (HSAB) Concept
VIII. Beyond the Isoelectronic and Isolobal
Analogies
IX. Atomic Valence and the Colored Periodic Table

GLOSSARY basis for the periodic classification of the elements.
Bond disociation energy (BDE) The energy differ-
Arrow formula Representation of molecules by append- ence between two atoms infinitely separated and at
ing directional arrows on the valence atomic orbitals equilibrium geometry.
according to the electron occupancy. E-bond Bond due to Coulombic attraction of electron
Atom Smallest characteristic constituent particle of an pairs and holes in the absence of charge transfer.
element. Electron Fundamental subatomic particle with a charge
Atomic mass (atomic weight) Relative mass of an atom. of 1.602*10 −19 C and a rest mass of 9.110*10 −31 kg.
By current international agreement, the standard for all The number and arrangement of electrons in atoms
atomic masses is the isotope carbon-12, which is arbi- is largely responsible for the chemical properties of
trarily assigned an atomic mass of exactly 12. Atomic elements and many of their physical properties.
mass was the original numerical basis for the periodic Electron configuration The arrangement of electrons in
table. the various energy levels, sublevels, and orbitals of an
Atomic number Number of protons in the nucleus of atom.
an atom. It is also the nuclear charge (in conventional Electron shells (levels) Principal energy levels occupied
electronic units) and the number of electrons in a neu- by the electrons in an atom, specified by the principal
tral atom. The atomic number is the current numerical quantum number n.

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