A period 6 element is one of the chemical elements in the sixth row (or period) of the periodic table of the chemical elements, including the lanthanides. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The sixth period contains 32 elements, tied for the most with period 7, beginning with caesium and ending with radon. Lead is currently the last stable element; all subsequent elements are radioactive. For bismuth, however, its only primordial isotope, 209Bi, has a half-life of more than 1019 years, over a billion times longer than the current age of the universe. As a rule, period 6 elements fill their 6s shells first, then their 4f, 5d, and 6p shells, in that order; however, there are exceptions, such as gold.
Properties This period contains the lanthanides, also known as the rare earths. Many lanthanides are known for their magnetic properties, such as neodymium. Many period 6 transition metals are very valuable, such as gold, however many period 6 other metals are incredibly toxic, such as thallium. Period 6 contains the last stable element, lead. All subsequent elements in the periodic table are radioactive. After bismuth, which has a half-life or more than 1019 years, polonium, astatine, and radon are some of the shortest-lived and rarest elements known; less than a gram of astatine is estimated to exist on earth at any given time.
Atomic characteristics {| class="wikitable sortable" ! colspan="3" | Chemical element ! Block ! Electron configuration |- bgcolor="" || 55 || Cs || Caesium || s-block || [Xe] 6s1 |- bgcolor="" || 56 || Ba || Barium || s-block || [Xe] 6s2 |- bgcolor="" || 57 || La || Lanthanum || f-block || [Xe] 5d1 6s2 |- bgcolor="" || 58 || Ce || Cerium || f-block || [Xe] 4f1 5d1 6s2 |- bgcolor="" || 59 || Pr || Praseodymium || f-block || [Xe] 4f3 6s2 |- bgcolor="" || 60 || Nd || Neodymium || f-block || [Xe] 4f4 6s2 |- bgcolor="" || 61 || Pm || Promethium || f-block || [Xe] 4f5 6s2 |- bgcolor="" || 62 || Sm || Samarium || f-block || [Xe] 4f6 6s2 |- bgcolor="" || 63 || Eu || Europium || f-block || [Xe] 4f7 6s2 |- bgcolor="" || 64 || Gd || Gadolinium || f-block || [Xe] 4f7 5d1 6s2 |- bgcolor="" || 65 || Tb || Terbium || f-block || [Xe] 4f9 6s2 |- bgcolor="" || 66 || Dy || Dysprosium || f-block || [Xe] 4f10 6s2 |- bgcolor="" || 67 || Ho || Holmium || f-block || [Xe] 4f11 6s2 |- bgcolor="" || 68 || Er || Erbium || f-block || [Xe] 4f12 6s2 |- bgcolor="" || 69 || Tm || Thulium || f-block || [Xe] 4f13 6s2 |- bgcolor="" || 70 || Yb || Ytterbium || f-block || [Xe] 4f14 6s2 |- bgcolor="" || 71 || Lu || Lutetium || d-block || [Xe] 4f14 5d1 6s2 |- bgcolor="" || 72 || Hf || Hafnium || d-block || [Xe] 4f14 5d2 6s2 |- bgcolor="" || 73 || Ta || Tantalum || d-block || [Xe] 4f14 5d3 6s2 |- bgcolor="" || 74 || W || Tungsten || d-block || [Xe] 4f14 5d4 6s2 |- bgcolor="" || 75 || Re || Rhenium || d-block || [Xe] 4f14 5d5 6s2 |- bgcolor="" || 76 || Os || Osmium || d-block || [Xe] 4f14 5d6 6s2 |- bgcolor="" || 77 || Ir || Iridium || d-block || [Xe] 4f14 5d7 6s2 |- bgcolor="" || 78 || Pt || Platinum || d-block || [Xe] 4f14 5d9 6s1 |- bgcolor="" || 79 || Au || Gold || d-block || [Xe] 4f14 5d10 6s1 |- bgcolor="" || 80 || Hg || Mercury || d-block || [Xe] 4f14 5d10 6s2 |- bgcolor="" || 81 || Tl || Thallium || p-block || [Xe] 4f14 5d10 6s2 6p1 |- bgcolor="" || 82 || Pb || Lead || p-block || [Xe] 4f14 5d10 6s2 6p2 |- bgcolor="" || 83 || Bi || Bismuth || p-block || [Xe] 4f14 5d10 6s2 6p3 |- bgcolor="" || 84 || Po || Polonium || p-block || [Xe] 4f14 5d10 6s2 6p4 |- bgcolor="" || 85 || At || Astatine || p-block || [Xe] 4f14 5d10 6s2 6p5 |- bgcolor="" || 86 || Rn || Radon || p-block || [Xe] 4f14 5d10 6s2 6p6
In many periodic tables, the f-block is erroneously shifted one element to the right, so that lanthanum and actinium become d-block elements, and Ce–Lu and Th–Lr form the f-block, tearing the d-block into two very uneven portions. This is a holdover from early erroneous measurements of electron configurations. Lev Landau and Evgeny Lifshitz pointed out in 1948 that lutetium is not an f-block element, and since then physical, chemical, and electronic evidence has overwhelmingly supported that the f-block contains the elements La–Yb and Ac–No, as shown here and as supported by International Union of Pure and Applied Chemistry reports dating from 1988 and 2021. An exception to the Madelung rule.
s-block elements
Caesium
Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C (82 °F), which makes it one of only five elemental metals that are liquid at (or near) room temperature. Caesium is an alkali metal and has physical and chemical properties similar to those of rubidium and potassium. The metal is extremely reactive and pyrophoric, reacting with water even at−116 °C (−177 °F). It is the least electronegative element having a stable isotope, caesium-133. Caesium is mined mostly from pollucite, while the radioisotopes, especially caesium-137, a fission product, are extracted from waste produced by nuclear reactors.
Two German chemists, Robert Bunsen and Gustav Kirchhoff, discovered caesium in 1860 by the newly developed method of flame spectroscopy. The first small-scale applications for caesium have been as a "getter" in vacuum tubes and in photoelectric cells. In 1967, a specific frequency from the emission spectrum of caesium-133 was chosen to be used in the definition of the second by the International System of Units. Since then, caesium has been widely used in atomic clocks.
Since the 1990s, the largest application of the element has been as caesium formate for drilling fluids. It has a range of applications in the production of electricity, in electronics, and in chemistry. The radioactive isotope caesium-137 has a half-life of about 30 years and is used in medical applications, industrial gauges, and hydrology. Although the element is only mildly toxic, it is a hazardous material as a metal and its radioisotopes present a high health risk in case of radioactivity releases.
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with water and carbon dioxide and is not found as a mineral. The most common naturally occurring minerals are the very insoluble barium sulfate, BaSO4 (barite), and barium carbonate, BaCO3(witherite). Barium's name originates from Greek barys (βαρύς), meaning "heavy", describing the high density of some common barium-containing ores.
Barium has few industrial applications, but the metal has been historically used to scavenge air in vacuum tubes. Barium compounds impart a green color to flames and have been used in fireworks. Barium sulfate is used for its density, insolubility, and X-ray opacity. It is used as an insoluble heavy additive to oil well drilling mud, and in purer form, as an X-ray radiocontrast agent for imaging the human gastrointestinal tract. Soluble barium compounds are poisonous due to release of the soluble barium ion, and have been used as rodenticides. New uses for barium continue to be sought. It is a component of some "high temperature" YBCOsuperconductors, and electroceramics.
f-block elements (lanthanides)
The lanthanide or lanthanoid (IUPAC nomenclature)The current IUPAC recommendation is that the name lanthanoid be used rather than lanthanide, as the suffix "-ide" is preferred for negative ions whereas the suffix "-oid" indicates similarity to one of the members of the containing family of elements. However, lanthanide is still favored in most (~90%) scientific articles and is currently adopted on Wikipedia. In the older literature, the name "lanthanon" was often used. series comprises the fifteen metallic chemical elements with atomic numbers 57 through 71, from lanthanum through lutetium.Lanthanide , Encyclopædia Britannica on-line These fifteen elements, along with the chemically similar elements scandium and yttrium, are often collectively known as the rare-earth elements.
The informal chemical symbol Ln is used in general discussions of lanthanide chemistry. All but one of the lanthanides are f-block elements, corresponding to the filling of the 4f electron shell; lanthanum, a d-block element, is also generally considered to be a lanthanide due to its chemical similarities with the other fourteen. All lanthanide elements form trivalent cations, Ln3+, whose chemistry is largely determined by the ionic radius, which decreases steadily from lanthanum to lutetium.
Chemical elementLaCePrNdPmSmEuGdTbDyHoErTmYbLu Atomic number575859606162636465666768697071Image Density (g/cm3)6.162 6.770 6.77 7.01 7.26 7.52 5.244 7.90 8.23 8.540 8.79 9.066 9.32 6.90 9.841Melting point (°C)920 795 935 1024 1042 1072 826 1312 1356 1407 1461 1529 1545 824 1652 Atomic electron configuration*5d14f15d14f3 4f4 4f54f64f7 4f75d14f94f104f114f124f134f144f145d1 Ln3+ electron configuration*4f0Lanthanum – Chemistry Encyclopedia – reaction, water, elements, metal, gas, name, atom. Chemistryexplained.com. Retrieved on 2012-01-15. 4f14f2 4f3 4f44f54f6 4f74f8 4f9 4f104f114f12 4f134f14 Ln3+ radius (pm) 103 102 99 98.3 97 95.8 94.7 93.8 92.3 91.2 90.1 8988 86.8 86.1 Between initial [Xe] and final 6s2 electronic shells
The lanthanide elements are the group of elements with atomic number increasing from 57 (lanthanum) to 71 (lutetium). They are termed lanthanide because the lighter elements in the series are chemically similar to lanthanum. Strictly speaking, both lanthanum and lutetium have been labeled as group 3 elements, because they both have a single valence electron in the d shell. However, both elements are often included in any general discussion of the chemistry of the lanthanide elements.
In presentations of the periodic table, the lanthanides and the actinides are customarily shown as two additional rows below the main body of the table, with placeholders or else a selected single element of each series (either lanthanum or lutetium, and either actinium or lawrencium, respectively) shown in a single cell of the main table, between barium and hafnium, and radium and rutherfordium, respectively. This convention is entirely a matter of aesthetics and formatting practicality; a rarely used wide-formatted periodic table inserts the lanthanide and actinide series in their proper places, as parts of the table's sixth and seventh rows (periods).
d-block elements
Lutetium
Lutetium ( ) is a chemical element with the symbol Lu and atomic number 71. It is the last element in the lanthanide series, which, along with the lanthanide contraction, explains several important properties of lutetium, such as it having the highest hardness or density among lanthanides. Unlike other lanthanides, which lie in the f-block of the periodic table, this element lies in the d-block; however, lanthanum is sometimes placed on the d-block lanthanide position. Chemically, lutetium is a typical lanthanide: its only common oxidation state is +3, seen in its oxide, halides and other compounds. In an aqueous solution, like compounds of other late lanthanides, soluble lutetium compounds form a complex with nine water molecules.