Iridium is the seventy seventh element on the periodic table, giving it seventy seven protons and electrons. Despite being one of the rarest elements in the Earth’s crust, iridium is relatively common in meteorites. In nature it can be found as the free element or in naturally occurring alloys such as iridium–osmium alloys.
On the periodic table, the element is characterized as a transition metal. Given the sheer number of transition metals it is difficult to define any definite characteristics but, generally, transition metals are paramagnetic with more than one oxidation states. Also, metals typically (though not always) have high electrical conductivity as well as high density and high melting and boiling points.
Along with five other elements, iridium is also a member of the platinum group. These six metals are highly resistant to wear and tarnish as well as chemical attack, have excellent high-temperature characteristics, and stable electrical properties.
Iridium is considered to be the second most dense stable element, after osmium, and is a hard brittle metal with a high melting point. It has two naturally occurring stable isotopes.
Though there has been some debate about the densest element, most recent calculations of density agree that osmium is indeed the densest element, beating iridium by about 0.03 g/cm3 (iridium is measured at around 22.56 g/cm3 while osmium is measured at around 22.59 g/cm3).
German chemist Martin Heinrich Klaproth is credited with the discovery of this element in 1789 which he named after the planet Uranus. Uranus itself was named after the Greek god of the sky and had been discovered only eight years prior.
The metal itself wasn’t isolated until 1841 by Eugène-Melchior Péligot.
Various cubes and cuboids of uranium produced during the Manhattan Project as well as the element’s crystal structure at room temperature, orthorhombic.
Uranium is the ninety second element on the periodic table, giving it ninety two protons and electrons. A radioactive element, uranium is naturally occurring and can be found in over one hundred minerals. The most common uranium ore is uraninite.
The element is typically characterized as a transition metal, or sometimes as an inner transition metal. Given the sheer number of transition metals it is difficult to define any definite characteristics but, generally, transition metals are paramagnetic with more than one oxidation states. Also, metals typically (though not always) have high electrical conductivity as well as high density and high melting and boiling points.
Within the transition metals, uranium is classified as an actinide. Actinides have large atomic and ionic radii, and display a wide range of physical properties among themselves. After plutonium, the rest of the actinides are synthetic elements. Plutonium, uranium, and thorium are primordial elements while neptunium, protactinium, and actinium are the result of the decay of other elements.
A silvery white, weakly radioactive metal, uranium is as hard as titanium or niobium and only slightly less dense than tungsten and gold. It is malleable, ductile, slightly paramagnetic, strongly electropositive and a poor electrical conductor, occurring as one of three allotropic forms. Three of the isotopes of this element are naturally occurring.
This actinide is one of the rarest and most expensive naturally occurring elements with a pure cost of about $280 per gram. The largest amount of protactinium ever obtained was 125 g in 1961 from the Great Britain Atomic Energy Authority, using about 60 tons of nuclear waste material.
Ruthenium doesn’t react with air, water, or acids, but it can react explosively with oxygen at higher temperatures as well as molten alkali and halogens.
Periodic Videos on YouTube talks about the naming of the element ruthenium, its discovery, its reactivity, and its applications as a catalyst. In powdered form, ruthenium appears much darker than its normal silver color, as shown.
Despite ruthenium’s well known properties as a catalyst, fifty percent of ruthenium is used for electronics applications - such as alloyed with platinum or palladium to make wear-resistant electrical contacts or in the form of ruthenium dioxide and lead and bismuth ruthenates for thick film chip resistors. Occasionally, ruthenium is also used in other alloys, such as titanium alloys or superalloys.
Other applications of the element include chemical vapor deposition for data storage, radiotherapy of eye tumors, as optode sensors for oxygen, and potentially solar energy technology.
With no stable isotopes, actinium’s radioactivity requires that precautions be taken when dealing with this element. It’s radioactivity, however, also enables its use in nuclear medicine.
The first non-primordial radioactive element to be isolated in 1899, actinium lends its name to the rest of its group as well, the actinides. French chemist André-Louis Debierne separated it from pitchblende residues left after Marie and Pierre Curie extracted radium. Its name comes from the Ancient Greek aktis, aktinos (ακτίς, ακτίνος), meaning beam or ray.
Probably the most well known application for uranium is also its main civilian use: fuel for nuclear power plants. In fact, one kilogram of uranium-235 can theoretically produce about 20 terajoules of energy (2×1013 joules), assuming complete fission occurs. Other, much less common applications of uranium include in glass and pottery glazes, glow-in-the-dark paints, in photographic chemicals, in lamp filaments, in dentures, and various types of radiometric dating.
Military applications of this element include high-density penetrators, made from depleted uranium alloyed with other elements such as titanium or molybdenum, and as a shielding material to store and transport radioactive materials.
Finally, uranium-235 has been used as the fissile explosive material to produce nuclear weapons.
Though uranium is known for its radioactivity, it is actually weakly radioactive compared with many other elements. In fact, when it comes to depleted uranium, the main hazard is chemical poisoning by uranium oxide, not its radioactivity. However, this is not to say that the risk doesn’t exist - uranium miners are known to have a higher incidence of cancer and the Occupational Safety and Health Administration (OSHA) has set the permissible exposure limit for uranium exposure in the workplace as 0.25 mg/m3 over an 8-hour workday.
Because uranium is a naturally occurring element, and more common than many other elements (it is forty times more abundant than silver) it can be found in soil, rocks, and water, and is used by several microorganisms. Some bacteria use uranium for their growth, converting uranium(VI) into uranium(IV), while others can absorb concentrations of uranium that are up to 300 times the level of their environment. Uranium can also be found in low concentrations in plants and animals, absorbed through the soil in the case of plants or consumed by animals.
Aside from being radioactive, uranium is a toxic metal, and normal functioning of the kidney, brain, liver, heart, and other systems can be affected by uranium exposure. Many human and animal studies have been done on the effect of uranium on various body systems and a table from 2004 summarizing these studies can be found here.
Since arsenic is toxic to many forms of life, including insects, bacteria, and fungi, it was commonly used as a wood preservative in the form of chromated copper arsenate, though it has since been banned in many countries. It is also being phased out of use in various agricultural insecticides and poisons
Metallic arsenic is often alloyed with lead, to strengthen the metal, or gallium, to create semiconductors.
Lanthanum is the fifty seventh element on the periodic table, giving it fifty seven protons and electrons. It is the twenty eighth most abundant element in the Earth’s crust, and is often found alongside cerium.
The element is typically characterized as a transition metal, or sometimes as an inner transition metal. Given the sheer number of transition metals it is difficult to define any definite characteristics but, generally, transition metals are paramagnetic with more than one oxidation states. Also, metals typically (though not always) have high electrical conductivity as well as high density and high melting and boiling points.
With the transition metals, lanthanum is classified as a lanthanide, from which element the group takes its name. All lanthanides are considered rare earth elements on the periodic table. Despite the name however, rare earth elements are not necessarily rare - they’re just notoriously hard to find in large enough quantities to be useful. Often found together, rare earth elements are difficult to separate.
Lanthanum is a soft, ductile, silvery white metal that has several allotropes and only one naturally occurring stable isotope.
