Dubnium

General properties
Name, symbol, number	dubnium, Db, 105
Element category	transition metal
Group, period, block	5, 7, d
Standard atomic weight	(268)
Electron configuration	[Rn] 5f14 6d3 7s2 (predicted) 2, 8, 18, 32, 32, 11, 2 (predicted)
History
Discovery	Joint Institute for Nuclear Research (1968)

Dubnium is a chemical element with the symbol Db and atomic number105, named after the town of Dubna in Russia, where it was first produced. It is a synthetic element (an element that can be created in a laboratory but is not found in nature) and radioactive; the most stable known isotope, dubnium-268, has a half-life of approximately 28 hours.

In the periodic table of the elements, it is a d-block element and in the transactinide elements. It is a member of the 7th period and belongs to the group 5 element. Chemistry experiments have confirmed that dubnium behaves as the heavier homologue to tantalum in group 5. The chemical properties of dubnium are characterized only partly. They are similar with those of other group 5 elements.

In the 1960s, microscopic amounts of dubnium were produced in laboratories in the former Soviet Union and in California. The priority of the discovery and therefore the naming of the element was disputed between Soviet and American scientists, and it was not until 1997 that International Union of Pure and Applied Chemistry(IUPAC) established dubnium as the official name for the element.

Return to Periodic Table

Rutherfordium

General properties
Name, symbol, number	rutherfordium, Rf, 104
Element category	transition metal
Group, period, block	4, 7, d
Standard atomic weight	(267)
Electron configuration	[Rn] 5f14 6d2 7s2 2, 8, 18, 32, 32, 10, 2
History
Discovery	Joint Institute for Nuclear Research (1964)

Rutherfordium is a chemical element with symbol Rf and atomic number 104, named in honor of New Zealand physicist Ernest Rutherford. It is a synthetic element(an element that can be created in a laboratory but is not found in nature) and radioactive; the most stable known isotope, ²⁶⁷Rf, has a half-life of approximately 1.3 hours.

In the periodic table of the elements, it is a d-block element and the first of the transactinide elements. It is a member of the 7th period and belongs to the group 4 elements. Chemistry experiments have confirmed that rutherfordium behaves as the heavier homologue to hafnium in group 4. The chemical properties of rutherfordium are characterized only partly. They compare well with the chemistry of the other group 4 elements, even though some calculations had indicated that the element might show significantly different properties due to relativistic effects.

In the 1960s, small amounts of rutherfordium were produced in laboratories in the former Soviet Union and in California. The priority of the discovery and therefore the naming of the element was disputed between Soviet and American scientists, and it was not until 1997 that International Union of Pure and Applied Chemistry (IUPAC) established rutherfordium as the official name for the element.

Return to Periodic Table

Radium

General properties
Name, symbol, number	radium, Ra, 88
Element category	alkali metal
Group, period, block	2, 7, s
Standard atomic weight	(226)
Electron configuration	[Rn] 7s2 2, 8, 18, 32, 18, 8, 2
History
Discovery	Pierre Curie and Marie Curie (1898)
First isolation	Marie Curie (1902)

Radium is a chemical element with symbol Ra and atomic number 88. Radium is an almost pure-white alkaline earth metal, but it readily oxidizes on exposure to air, becoming black in color. All isotopes of radium are highly radioactive, with the most stable isotope being radium-226, which has a half-life of 1601 years and decays into radon gas. Because of such instability, radium is luminescent, glowing a faint blue.

Radium, in the form of radium chloride, was discovered by Marie Skłodowska-Curie and Pierre Curie in 1898. They extracted the radium compound from uraninite and published the discovery at the French Academy of Sciences five days later. Radium was isolated in its metallic state by Marie Curie and André-Louis Debierne through the electrolysis of radium chloride in 1910. Since its discovery, it has given names like radium A and radium C₂ to several isotopes of other elements that are decay products of radium-226.

In nature, radium is found in uranium ores in trace amounts as small as a seventh of a gram per ton of uraninite. Radium is not necessary for living organisms, and adverse health effects are likely when it is incorporated into biochemical processes because of its radioactivity and chemical reactivity.

Return to Periodic Table

Francium

General properties
Name, symbol, number	francium, Fr, 87
Element category	alkali metal
Group, period, block	1, 7, s
Standard atomic weight	(223)
Electron configuration	[Rn] 7s1 2, 8, 18, 32, 18, 8, 1
History
Discovery	Marguerite Perey (1939)
First isolation	Marguerite Perey (1939)

Francium is a chemical element with symbol Fr and atomic number 87. It was formerly known as eka-caesium and actinium K. It is one of the two least electronegative elements, the other being caesium. Francium is a highly radioactive metal that decays into astatine, radium, and radon. As an alkali metal, it has one valence electron.

Bulk francium has never been viewed. Because of the general appearance of the other elements in its periodic table column, it is assumed that francium would appear as a highly reflective metal, if enough could be collected together to be viewed as a bulk solid or liquid. However preparing such a sample is impossible, since the extreme heat of decay (its longest isotopic half life is only 22 minutes) would immediately vaporize any viewable quantity of the element.

Francium was discovered by Marguerite Perey in France (from which the element takes its name) in 1939. It was the last element discovered in nature, rather than by synthesis. Outside the laboratory, francium is extremely rare, with trace amounts found in uranium and thorium ores, where the isotope francium-223 continually forms and decays. As little as 20–30 g (one ounce) exists at any given time throughout the Earth's crust; the other isotopes are entirely synthetic. The largest amount produced in the laboratory was a cluster of more than 300,000 atoms.

Return to Periodic Table

Radon

General properties
Name, symbol, number	radon, Rn, 86
Element category	noble gases
Group, period, block	18, 6, p
Standard atomic weight	(222)
Electron configuration	[Xe] 4f14 5d10 6s2 6p6 2, 8, 18, 32, 18, 8
History
Discovery	Friedrich Ernst Dorn (1898)
First isolation	William Ramsay and Robert Whytlaw-Gray (1910)

Radon is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as an indirect decay product of uranium or thorium. Its most stable isotope, ²²²Rn, has a half-life of 3.8 days. Radon is one of the densest substances that remains a gas under normal conditions. It is also the only gas under normal conditions that only has radioactive isotopes, and is considered a health hazard due to its radioactivity. Intense radioactivity has also hindered chemical studies of radon and only a few compounds are known.

Radon is formed as one intermediate step in the normal radioactive decay chains, through which thorium and uranium slowly decay into lead. Thorium and uranium are the two most common radioactive elements on earth; they have been around since the earth was formed. Their naturally occurring isotopes have very long half-lives, on the order of billions of years. Thorium and uranium, their decay product radium, and its decay product radon, will therefore continue to occur for tens of millions of years at almost the same concentrations as they do now. As radon itself decays, it produces new radioactive elements called radon daughters or decay products. Unlike the gaseous radon itself, radon daughters are solids and stick to surfaces, such as dust particles in the air. If such contaminated dust is inhaled, these particles can stick to the airways of the lung and increase the risk of developing lung cancer.

Unlike all the other intermediate elements in the aforementioned decay chains, radon is gaseous and so easily inhaled. Thus, even in this age of nuclear reactors, naturally-occurring radon is responsible for the majority of the public exposure to ionizing radiation. It is often the single largest contributor to an individual's background radiation dose, and is the most variable from location to location. Despite its short lifetime, some radon gas from natural sources can accumulate to far higher than normal concentrations in buildings, especially in confined areas such as attics and basements. It can also be found in some spring waters and hot springs.

Epidemiological studies have shown a clear link between breathing high concentrations of radon and incidence of lung cancer. Thus, radon is considered a significant contaminant that affects indoor air quality worldwide. According to the United States Environmental Protection Agency, radon is the second most frequent cause of lung cancer, after cigarette smoking, causing 21,000 lung cancer deaths per year in the United States. About 2,900 of these deaths occur among people who have never smoked. While radon is the second most frequent cause of lung cancer, it is the number one cause among non-smokers, according to EPA estimates.

Return to Periodic Table

Astatine

General properties
Name, symbol, number	astatine, At, 85
Element category	halogen
Group, period, block	17, 6, p
Standard atomic weight	(210)
Electron configuration	[Xe] 4f14 5d10 6s2 6p5 2, 8, 18, 32, 18, 7
History
Discovery	Dale R. Corson, Kenneth Ross MacKenzie, Emilio Segrè(1940)

Astatine is a radioactive chemical element with the chemical symbol At and atomic number 85. It occurs on Earth only as the result of the radioactive decay of certain heavier elements. All of its isotopes are short-lived; the most stable is astatine-210, with a half-life of 8.1 hours. Accordingly, much less is known about astatine than most other elements. The observed properties are consistent with it being a heavier analog of iodine; many other properties have been estimated based on this resemblance.

Elemental astatine has never been viewed, because a mass large enough to be seen (by the naked human eye) would be immediately vaporized by the heat generated by its own radioactivity. Astatine may be dark, or it may have a metallic appearance and be a semiconductor, or it may even be a metal. It is likely to have a much higher melting point than does iodine, on par with those of bismuth and polonium. Chemically, astatine behaves more or less as a halogen, being expected to form ionic astatides with alkali or alkaline earth metals; it is known to form covalent compounds with nonmetals, including other halogens. It does, however, also have a notable cationic chemistry that distinguishes it from the lighter halogens. The second longest-lived isotope of astatine, astatine-211, is the only one currently having any commercial application, being employed in medicine to diagnose and treat some diseases via its emission of alpha particles (helium-4 nuclei). Only extremely small quantities are used, however, due to its intense radioactivity.

The element was first produced by Dale R. Corson, Kenneth Ross MacKenzie, and Emilio Segrè at the University of California, Berkeley in 1940. They named the element "astatine", a name coming from the great instability of the synthesized matter (the source Greek word αστατος (astatos) means "unstable"). Three years later it was found in nature, although it is the least abundant element in the Earth's crust among the non-transuranic elements, with an estimated total amount of less than 28 grams (1 oz) at any given time. Six astatine isotopes, with mass numbers of 214 to 219, are present in nature as the products of various decay routes of heavier elements, but neither the most stable isotope of astatine (with mass number 210) nor astatine-211 (which is used in medicine) is produced naturally.

Return to Periodic Table

Polonium

General properties
Name, symbol, number	polonium, Po, 84
Element category	post-transition metal
Group, period, block	16, 6, p
Standard atomic weight	(209)
Electron configuration	[Xe] 6s2 4f14 5d10 6p4 2, 8, 18, 32, 18, 6
History
Discovery	Pierre Curie and Marie Curie (1898)
First isolation	Willy Marckwald (1902)

Polonium is a chemical element with the symbol Po and atomic number 84, discovered in 1898 by Marie and Pierre Curie. A rare and highly radioactive element with no stable isotopes, polonium is chemically similar to bismuth and tellurium, and it occurs in uranium ores. Applications of polonium are few, and include heaters in space probes, antistatic devices, and sources of neutrons and alpha particles. Because of its position in the periodic table, polonium is sometimes referred to as a metalloid, however others note that on the basis of its properties and behavior it is "unambiguously a metal".

Return to Periodic Table