Atomic Number 81
In the modern periodic table, the elements are listed in order of increasing atomic number. The atomic number is the number of protons in the nucleus of an atom. The number of protons define the identity of an element (i.e., an element with 6 protons is a carbon atom, no matter how many neutrons may be present). The number of protons determines how many electrons surround the nucleus, and it is the arrangement of these electrons that determines most of the chemical behavior of an element.
In a periodic table arranged in order of increasing atomic number, elements having similar chemical properties naturally line up in the same column (group). For instance, all of the elements in Group 1A are relatively soft metals, react violently with water, and form 1+ charges; all of the elements in Group 8A are unreactive, monatomic gases at room temperature, etc. In other words, there is a periodic repetition of the properties of the chemical elements with increasing mass.
In the original periodic table published by Dimitri Mendeleev in 1869, the elements were arranged according to increasing atomic mass— at that time, the nucleus had not yet been discovered, and there was no understanding at all of the interior structure of the atom, so atomic mass was the only guide to use. Once the structure of the nucleus was understood, it became clear that it was the atomic number that governed the properties of the elements.
Isotope data for bromine-81 in the Periodic Table Isotopes of Bromine (click to see decay chain): 67 Br 68 Br 69 Br 70 Br 71 Br 72 Br 73 Br 74 Br 75 Br 76 Br 77 Br 78 Br 79 Br 80 Br 81 Br 82 Br 83 Br 84 Br 85 Br 86 Br 87 Br 88 Br 89 Br 90 Br 91 Br 92 Br 93 Br 94 Br 95 Br 96 Br 97 Br. Thallium is a chemical element with the symbol Tl and atomic number 81. It is a gray post-transition metal that is not found free in nature. When isolated, thallium resembles tin, but discolors when exposed to air. Chemists William Crookes and Claude-Auguste Lamy discovered thallium independently in 1861, in residues of sulfuric acid production. Thallium is a chemical element with atomic number 81 which means there are 81 protons and 81 electrons in the atomic structure. The chemical symbol for Thallium is Tl. The atom consist of a small but massive nucleus surrounded by a cloud of rapidly moving electrons. The nucleus is composed of protons and neutrons.
Also found in: Thesaurus.| Noun | 1. | atomic number 81 - a soft grey malleable metallic element that resembles tin but discolors on exposure to air; it is highly toxic and is used in rodent and insect poisons; occurs in zinc blende and some iron ores thallium, Tl metal, metallic element - any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc. blende, sphalerite, zinc blende - an ore that is the chief source of zinc; consists largely of zinc sulfide in crystalline form |
Thallium Atomic Number
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Bromine 81
Element Atomic Number 81