GLENN SEABORG AND SEABORGIUM BASIC INFORMATION AND TUTORIALS

Prior to 1940 the periodic table ended at uranium, element number 92. Since that time, no scientist has had a greater effect on the periodic table than Glenn Seaborg.

In 1940 Seaborg, Edwin McMillan, and coworkers at the University of California, Berkeley, succeeded in isolating plutonium (Pu) as a product of the reaction between uranium and neutrons.

Between 1944 and 1958, Seaborg and his coworkers also identified various products of nuclear reactions as being the elements having atomic numbers 95 through 102. All these elements are radioactive and are not found in nature; they can be synthesized only via nuclear reactions.

For their efforts in identifying the elements beyond uranium (the transuranium elements), McMillan and Seaborg shared the 1951 Nobel Prize in Chemistry.

From 1961 to 1971, Seaborg served as the chairman of the US Atomic Energy Commission (now the Department of Energy). In this position he had an important role in establishing international treaties to limit the testing of nuclear weapons.

Upon his return to Berkeley, he was part of the team that in 1974 first identified element number 106. In 1994, to honor Seaborg’s many contributions to the discovery of new elements, the American Chemical Society proposed that element number 106 be named seaborgium (Sg).

After several years of controversy about whether an element should be named after a living person, the IUPAC officially adopted the name in 1997. Seaborg became the first person to have an element named after him while he was alive.

HOW WAS THE EARTH FORMED? - BASIC INFORMATION ON THE FORMATION OF PLANET EARTH

The solar system formed about 4.6 billion years ago. The Earth and other terrestrial planets are believed to have formed by gathering together the so-called planetesimals.

Planetesimals are formed by the coalescence of fine- or coarse-grained mineral matters, metals, and gases of various kinds. As planetesimals stuck together mostly by gravity and the body thus formed grew larger, it became a precursor of terrestrial planet.

Some of these bodies were smashed by other bodies, and their fragments became meteorites. Hence, studies of meteorites would provide a lot of insight into the formation and the earlier state of the Earth.

The planet Earth was thus formed. Heat was created as the coalescence (of planetesimals) proceeded due to gravity, and heat also came from radioactivity of several radioactive elements such as aluminum-26. So the newly formed body was heated and the core was melted.

As the material becomes liquid (as a result of melting), the materials contained in the liquid separate out according to their densities. The more dense material would sink closer to the bottom (core).

Thus, the present layer structure of the Earth formed. The innermost core is a dense solid of about 1,200 km radius, whose density is about 12.6 g per cubic centimeter (12.6 ×106 kg/m3).

It is made of mostly iron metal and a small amount of nickel. By the way, the density of iron metal is only 7.8×106 kg/m3 under the ordinary pressure. The next layer is the outer core (up to 3,500 km from the center of the Earth), which is liquid and has a density of 9.5–12×106 kg/m3. The chemical composition seems to be about the same as that of the inner core.

There is an abrupt change in density in the next layer, mantle. The width of mantle is about 2,900 km (3,500–6,380 km from the center). Its density ranges from 4 to 5.5 ×106 kg/m3. The mantle is made of mostly magnesium–iron silicates (silicon oxides). The outermost layer is the thin crust of about 35–45 km on the land portion, and about 6 km under the ocean portion.

MERCURY AND MERCURY POISONING - THE CONTROVERSIAL ELEMENT (THE APPLICATIONS AND DANGERS OF MERCURY)

Virtually all metals exist as solids at room temperature. Mercury is the only metallic element that is a liquid under normal conditions. If cooled to 39°C, it does freeze to a solid. Liquid mercury is shiny and metalliclooking.

You have probably heard a fair amount about the toxicity of mercury. As a liquid, it is not especially toxic when swallowed since most of it passes through the body unchanged.

However, mercury vapor is highly toxic, as are all compounds of mercury that dissolve in water to form solutions. Once they enter the body, these forms of mercury can attack the brain and produce mental and physiological disturbances.

An incident in Texarkana, on the Texas–Arkansas border, illustrated the hazards of handling mercury. Two teenagers stole 40 pounds of liquid mercury from a site where it had been used to make neon lights.

They poured it over themselves and on floors in their homes, gave it out to friends, and even dipped cigarettes into the liquid and smoked them. Within days they began to exhibit the signs of mercury poisoning: coughing up blood, vomiting, breathing difficulties, and seizures.

The end result was that eight contaminated homes were evacuated, a family dog was killed by the vapors, and more than 170 people in the town and surrounding areas received medical treatment for mercury exposure.

Mercury poisoning was much more common in the 19th century when workers who used mercury to cure felt hats developed twitches, spoke incoherently, and drooled as a result of long-term exposure to mercury vapors.

These workers provided Lewis Carroll with a model for the Mad Hatter in Alice in Wonderland. These days, most of the mercury that enters the environment comes from the incineration of waste and sewage sludge, and the burning of coal.

Recently, scrapping cars without removing the elemental mercury used in light switches and other components was identified as a significant source of the element to the environment.

MERCURY DANGERS IN DENTAL CARE?
Until quite recently, an alloy that most people had an intimate acquaintance with was the material used to fill cavities in decayed teeth. You may be surprised to learn that mercury was one of the metals used to fill teeth.

Although mercury is a liquid at room and body temperatures, it forms many alloys, called amalgams, that are solid at normal temperatures. Those having melting points in the 60°C range are useful for fillings, since they can be placed in the decay cavity as a warm liquid metal without causing the patient pain.

The liquid assumes the cavity shape as it cools and solidifies in place. Dental amalgam combines mercury with silver, which imparts resistance to tarnishing and mechanical strength, and about half as much tin, which readily amalgamates with mercury.

When first placed in a tooth, and whenever the filling is involved in the chewing of food, a tiny amount of the mercury is vaporized. Some scientists believe that mercury exposure from this source causes long-term health problems in some individuals, but an expert panel of the U.S. National Institute of Health concluded that dental amalgams do not pose a health risk.

A recent study of adults found that no measure of exposure to mercury—whether the level of the element in the urine or the number of dental fillings—correlated with any measure of mental functioning or fine motor control.

ATOMIC RADIUS - BASIC INFORMATION AND TUTORIALS

Unfortunately, atomic radius is hard to define. The probability of finding an electron decreases with increasing distance from the nucleus, but nowhere does the probability fall to zero, so there is no precise outer boundary to an atom.

We might describe an effective atomic radius as, say, the distance from the nucleus within which 95% of all the electron charge density is found, but in fact, all that we can measure is the distance between the nuclei of adjacent atoms (internuclear distance).

Even though it varies, depending on whether atoms are chemically bonded or merely in contact without forming a bond, we define atomic radius in terms of internuclear distance.

Because we are primarily interested in bonded atoms, we will emphasize an atomic radius based on the distance between the nuclei of two atoms joined by a chemical bond. The covalent radius is one-half the distance between the nuclei of two identical atoms joined by a single covalent bond.

The ionic radius is based on the distance between the nuclei of ions joined by an ionic bond. Because the ions are not identical in size, this distance must be properly apportioned between the cation and anion. One way to apportion the electron density between the ions is to define the radius of one ion and then infer the
radius of the other ion.

The convention we have chosen to use is to assign an ionic radius of 140 pm. An alternative apportioning scheme is to use as the reference ionic radius.

When using ionic radii data, one should carefully note which convention is used and not mix radii from the different conventions. Starting with a radius of 140 pm for the radius of Mg2+ can be obtained from the internuclear distance in MgO, the radius of from the internuclear distance in and the radius of from the internuclear distance in NaCl.

For metals, we define a metallic radius as one-half the distance between the nuclei of two atoms in contact in the crystalline solid metal. Similarly in a solid sample of a noble gas the distance between the centers of neighboring atoms is called the van der Waals radius.

There is much debate about the values of the atomic radii of noble gases because the experimental determination of the van der Waals radii is difficult; consequently, the atomic radii of noble gases are left out of the discussion of trends in atomic radii.

FEATURES OF PERIODIC TABLE OF ELEMENTS

Guide In Using The Periodic Table of Elements.


In the periodic table, elements are listed according to increasing atomic number starting at the upper left and arranged in a series of horizontal rows. This arrangement places similar elements in vertical groups, or families.

For example, sodium and potassium are found together in a group labeled 1 (called the alkali metals). We should expect other members of the group, such as cesium and rubidium, to have properties similar to sodium and potassium. Chlorine is found at the other end of the table in a group labeled 17.

Some of the groups are given distinctive names, mostly related to an important property of the elements in the group. For example, the group 17 elements are called the halogens, a term derived from Greek, meaning salt former.


Each element is listed in the periodic table by placing its symbol in the middle of a box in the table. The atomic number (Z) of the element is shown above the symbol, and the weighted-average atomic mass of the element is shown below its symbol. Some periodic tables provide other information, such as density and melting point, but the atomic number and atomic mass are generally sufficient for our needs.

Elements with atomic masses in parentheses, such as plutonium, Pu (244), are produced synthetically, and the number shown is the mass number of the most stable isotope. It is customary also to divide the elements into two broad categories metals and nonmetals. In figure below, colored backgrounds are used to distinguish the metals (tan) from the nonmetals (blue and pink).

Except for mercury, a liquid, metals are solids at room temperature. They are generally malleable (capable of being flattened into thin sheets), ductile (capable of being drawn into fine wires), and good conductors of heat and electricity, and have a lustrous or shiny appearance.

The properties of nonmetals are generally opposite those of metals; for example, nonmetals are poor conductors of heat and electricity. Several of the nonmetals, such as nitrogen, oxygen, and chlorine, are gases at room temperature.

Some, such as silicon and sulfur, are brittle solids. One bromine is a liquid. Two other highlighted categories in the figure are a special group of nonmetals known as the noble gases (pink), and a small group of elements, often called metalloids (green), that have some metallic and some nonmetallic properties.

The horizontal rows of the table are called periods. (The periods are numbered at the extreme left in the periodic table inside the front cover.) The first period of the table consists of just two elements, hydrogen and helium.

This is followed by two periods of eight elements each, lithium through neon and sodium through argon. The fourth and fifth periods contain 18 elements each, ranging from potassium through krypton and from rubidium through xenon.

The sixth period is a long one of 32 members. To fit this period in a table that is held to a maximum width of 18 members, 15 members of the period are placed at the bottom of the periodic table. This series of 15 elements start with lanthanum and these elements are called the lanthanides.

The seventh and final period is incomplete (some members are yet to be discovered), but it is known to be a long one. A15-member series is also extracted from the seventh period and placed at the bottom of the table. Because the elements in this series start with actinium they are called the actinides.

The labeling of the groups of the periodic table has been a matter of some debate among chemists. The 1-18 numbering system used is the one most recently adopted. Group labels previously used in the United States
consisted of a letter and a number, closely following the method adopted by Mendeleev, the developer of the periodic table.

As seen in the figure, the A groups 1 and 2 are separated from the remaining Agroups (3 to 8) by B groups 1 through 8. The International Union of Pure and Applied Chemistry (IUPAC) recommended the simple 1 to 18 numbering scheme in order to avoid confusion between the American number and letter system and that used in Europe, where some of the Aand B designations were switched! Currently, the IUPAC system is officially recommended by the American Chemical Society (ACS) and chemical societies in other nations. Because both numbering systems are in use, we show both in the figure and in the periodic table inside the front cover.