Question: What is the named isotope 's atomic number of the element with seven naturally occurring isotopes , none of which are stable ?

text: Chemical symbol
Symbols for named isotopes
The following is a list of isotopes of elements given in the previous tables which have been designated unique symbols . By this it is meant that a comprehensive list of current systematic symbols ( in the uAtom form ) are not included in the list and can instead be found in the Isotope index chart . The symbols for the named isotopes of hydrogen , deuterium ( D ) , and tritium ( T ) are still in use today , as is thoron ( Tn ) for radon-220 ( though not actinon ; An is usually used instead for a generic actinide ) . Heavy water and other deuterated solvents are commonly used in chemistry , and it is convenient to use a single character rather than a symbol with a subscript in these cases . The practice also continues with tritium compounds . When the name of the solvent is given , a lowercase d is sometimes used . For example , d6-benzene and C6D6 can be used instead of [ 2H6 ] C6H6 . [ 12 ] The symbols for isotopes of elements other than hydrogen and radon are no longer in use within the scientific community . Many of these symbols were designated during the early years of radiochemistry , and several isotopes ( namely those in the decay chains of actinium , radium , and thorium ) bear placeholder names using the early naming system devised by Ernest Rutherford . [ 13 ]
Chemical symbols are abbreviations used in chemistry for chemical elements , functional groups and chemical compounds. Element symbols for chemical elements normally consist of one or two letters from the Latin alphabet and are written with the first letter capitalised. Earlier symbols for chemical elements stem from classical Latin and Greek vocabulary. For some elements, this is because the material was known in ancient times, while for others, the name is a more recent invention. For example, Pb is the symbol for lead ( plumbum in Latin); Hg is the symbol for mercury ( hydrargyrum in Greek); and He is the symbol for helium (a new Latin name) because helium was not known in ancient Roman times. Some symbols come from other sources, like W for tungsten ( Wolfram in German) which was not known in Roman times. A 3-letter temporary symbol may be assigned to a newly synthesized (or not yet synthesized) element. For example, Uno was the temporary symbol for hassium (element 108) which had the temporary name of unniloctium , based on its atomic number being 8 greater than 100. There are also some historical symbols that are no longer officially used. In addition to the letters for the element itself, additional details may be added to the symbol as superscripts or subscripts a particular isotope , ionization , or oxidation state , or other atomic detail. A few isotopes have their own specific symbols rather than just an isotopic detail added to their element symbol.
Chemical symbol Name Atomic number Origin of symbol
Ac Actinium 89 From the Greek aktinos . Name restricted at one time to Ac , an isotope of actinium . This named isotope later became the official name for element 89
AcA Actinium A 84 From actinium and A. Placeholder name given at one time to Po , an isotope of polonium identified in the decay chain of actinium
AcB Actinium B 82 From actinium and B. Placeholder name given at one time to Pb , an isotope of lead identified in the decay chain of actinium
AcC Actinium C 83 From actinium and C. Placeholder name given at one time to Bi , an isotope of bismuth identified in the decay chain of actinium
AcC ' Actinium C ' 84 From actinium and C ' . Placeholder name given at one time to Po , an isotope of polonium identified in the decay chain of actinium
AcC Actinium C 81 From actinium and C . Placeholder name given at one time to Tl , an isotope of thallium identified in the decay chain of actinium
AcK Actinium K 87 Name given at one time to Fr , an isotope of francium identified in the decay chain of actinium
AcU Actino-uranium 92 Name given at one time to U , an isotope of uranium
AcX Actinium X 88 Name given at one time to Ra , an isotope of radium identified in the decay chain of actinium
An Actinon 86 From actin ium and emanati on . Name given at one time to Rn , an isotope of radon identified in the decay chain of actinium
D Deuterium 1 From the Greek deuteros . Name given to H
Io Ionium 90 Name given to Th , an isotope of thorium identified in the decay chain of uranium
MsTh 1 Mesothorium 1 88 Name given at one time to Ra , an isotope of radium
MsTh 2 Mesothorium 2 89 Name given at one time to Ac , an isotope of actinium
Pa Protactinium 91 From the Greek protos and actinium . Name restricted at one time to Pa , an isotope of protactinium . This named isotope later became the official name for element 91
Ra Radium 88 From the Latin radius . Name restricted at one time to Ra , an isotope of radium . This named isotope later became the official name for element 88
RaA Radium A 84 From radium and A. Placeholder name given at one time to Po , an isotope of polonium identified in the decay chain of radium
RaB Radium B 82 From radium and B. Placeholder name given at one time to Pb , an isotope of lead identified in the decay chain of radium
RaC Radium C 83 From radium and C. Placeholder name given at one time to Bi , an isotope of bismuth identified in the decay chain of radium
RaC ' Radium C ' 84 From radium and C ' . Placeholder name given at one time to Po , an isotope of polonium identified in the decay chain of radium