JTW's Chemistry Tutorials - Periodic Tables
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Periodic Tables
"The chemical elements are composed of... indivisible particles of matter, called atoms... atoms of the same element are identical in all respects, particularly weight." - John Dalton
The Modern Periodic Table
Mendeleev's Early Periodic Table 1871 and 1898, after Madame Curies Discovery of Radium
�I began to look about and write down the elements with their atomic weights and typical properties, analogous elements and like atomic weights on separate cards, and this soon convinced me that the properties of elements are in periodic dependence upon their atomic weights.�
Dmitri Ivanovich Mendeleev, 1905
Radium is Rd in this table, Today it is Ra
Understanding the Periodic Table
The Periodic Table is perhaps one of the most compact forms of human knowledge created to date. From the table, one may ascertain much that is of importance about the physical properties of the material world.
The Pictorial Periodic Table
Trends in the Periodic Table
The Size Trend for Atoms in their Neutral State
The increase in atomic size as we move down the verticle groups should come as no surprise, as we are placing electrons further out as we have already filled the orbitals close in.Note the contraction in atomic size when moving left to right across a period. This is due to being in the same shell but increasing the charge in the nucleus. The additional positive charge at the center pulls more strongly on all the electrons, thereby contracting the size as we move across the period. |
Electronegativity - The power of an atom in a molecule to attract electrons. The two widespread empirical scales of electronegativity are those developed by L. Pauling and R. Mulliken. The Pauling scale is thermochemical; it is based on the values of bond energies of type X-Y, X-X and Y-Y molecules from which the ionic contribution to the X-Y bond is defined as
DXY = EXY - (1/2)(EXX + EYY)
From this value the relative electronegativity of X with respect to Y is defined (in eV1/2 units) as
cX - cY (DXY)1/2
The Mulliken electronegativity ( in eV units) is given by the equation:
cX = (1/2) (IX + AX)
where IX and AX are respectively ionization potential and electron affinity in a suitable valence state (see valence state ionization potential, valence state electron affinity). both scales are linearly interrelated. These are useful for estimating bond polarities and strengths of bonds between different atoms. Many other scales of electronegativity are known, among which that of A. Allred and E. Rochow , where electronegativity is defined as the electrostatic force between the nucleus and its valence electrons, is most frequently used. Accounting for the observation that the position of bond points relates to the polarity of a bond, a scale of atomic and group electronegativities, which are comparable in magnitude to the Pauling values, was derived (R. Boyd) on the basis of topological properties of the electron density distributions in model hydrides R-H. ALLEN (1994); ALLRED and ROCHOW (1958); BERGMANN and HINZE (1996); BOYD and BOYD (1992); MULLIKEN (1934); PAULING (1932).
See also Absolute electronegativity, Equalization of electronegativity.
The Subshell/Orbital Blocks
"In 1944, I formulated the �actinide concept� of heavy element electronic structure.
This concept predicted that the fourteen actinides, including the first eleven transuranium elements, would form a transition series analogous to the rare-earth series of lanthanide elements and therefore show how the transuranium elements fit into the periodic table.
I was warned at the time that it was professional suicide to promote this idea, which has since been called one of the most significant changes in the periodic table since Mendeleev�s 19th century design. Luckily, I stuck to my guns and have seen the actinide concept become the foundation for many significant discoveries in heavy element research."
Glenn T. Seaborg
Metals, Nonmetals & Metalloids
- Metals - These elements occupy most of the periodic table, in particular the left side. They are malleable, ductile, and are good conductors of heat and electricity. They are ductile and malleable, easily able to be formed into wires and sheets. Metals generally pool their electrons accross the entire bulk material and therefore electrical current flows unrestricted across the material in accordance with any electrical potential that might be present. Metals are most likely to form cations when ionized.
- Group I - The Alkali Metals: Generally, the alkali metals are softer than the other metals. Cesium and francium are the most reactive alkali elements. Alkali metals may explode upon exposure to water. They form +1 cations in solution. Ox.# is +1 in compounds.
- Group II - The Alkaline Earth Metals: Because of their reactivity, the alkaline metals are not found free in nature. They form +2 cations in solution. Ox.# is +2 in compounds.
- The Transition Metals: A notable property of transition metals is that their valence electrons are present in more than just the outer shell. For this reason they are often capable of exhibiting multiple stable oxidation states. The transition metals Iron, Cobalt, and Nickel are the only elements capable of producing magnetic fields.
- The Rare Earth Elements: The thirty rare earth elements are composed of the lanthanide and actinide series. One element of the lanthanide series and most of the elements in the actinide series are called trans-uranium, which means synthetic or man-made. All of the rare earth metals are found in group 3 of the periodic table, and the 6th and 7th periods. The Rare Earth Elements are made up of two series of elements, the Lanthanide and Actinide Series.
- The Other Metals: These elements, unlike the transition elements, do not exhibit multiple oxidation states, and their valence electrons are only present in their outer shell. All of these elements are solid, have a relatively high density, and are opaque. They have oxidation numbers of +3, �4, and -3.
- Group I - The Alkali Metals: Generally, the alkali metals are softer than the other metals. Cesium and francium are the most reactive alkali elements. Alkali metals may explode upon exposure to water. They form +1 cations in solution. Ox.# is +1 in compounds.
- Metalloids - Also called, Semimetals or Semiconductors, Metalloids have properties of both metals and non-metals. Straddling the boundary between metal and non-metals, they can carry either a positive or negative electrical charge under special conditions. This property makes metalloids useful in computers and calculators where controlling the direction of current flow allows the formation of logic circuits.
- Boron: B, Silicon: Si, Germanium: Ge, Arsenic: As, Antimony: Sb, Tellurium: Te, Polonium: Po
- Non-metals - Non-metals tend to hold their electrons close to their nucleus and are therefore insulators, ie. poor conductors of electricity and heat. Unlike metals, the non-metallic elements are usually brittle, unmalleable, and not ductile. At room temperature, most Non-metals exist either as diatomic gases or solids, except Bromine which is a liquid at room temperature. The non-metals do not exhibit a metallic luster, nor do they reflect light. As ions they usually exist as anions.
The Diatomic Molecular Elements: Br2I2N2Cl2H2O2F2- Group VIIA - Halogens: The term "halogen" means "salt-former" and compounds containing halogens are called "salts". All halogens have 7 electrons in their outer shells, giving them an oxidation number of -1.
- Group VIIIA - Noble Gases: These elements were considered to be inert gases until the 1960's, because their oxidation number of 0 prevents the noble gases from forming compounds readily. All noble gases have the maximum number of electrons possible in their outer shell (2 for Helium, 8 for all others), making them stable.
- Carbon Elemental Molecular Forms: Soot, Graphite, Diamond, Buckministerfullerenes4
- Phosphorus Elemental Molecular Form: P4
- Sulfur Elemental Molecular Form: S8
- Selenium Elemental Molecular Form: Se8
Alternative Representations of the Periodic Table
A Graphical Electron Configuration Calculator
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