Period 6 element 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). Lanthanum is a chemical element with the symbol La and atomic number 57. It is the first element in the lanthanide series. It is a soft, ductile, silvery-white metal that tarnishes rapidly when exposed to air and is soft enough to be cut with a knife. It is the eponym of the lanthanide series,
Systematic element name for 4). There are two elision rules designed to prevent odd-looking names. The suffix "-ium" overrides traditional chemical suffix rules; thus elements 117 and 118 were "ununseptium" and "ununoctium", not "ununseptine" and "ununocton". This does not apply to the final trivial names these elements receive once confirmed; thus element 117 and 118 are now "tennessine" and "oganesson". For these trivial names, all elements receive the suffix "-ium", except those in group 17 which receive "-ine" (like the halogens) and those in group 18 which receive "-on" (like the noble gases). The systematic symbol is formed by taking the first letter