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,
Silver halide Silver halide A silver halide (or silver salt) is one of the chemical compounds that can form between the element silver and one of the halogens. In particular, bromine, chlorine, iodine and fluorine may each combine with silver to produce silver bromide (AgBr), silver chloride (AgCl), silver iodide (AgI), and three forms of silver fluoride, respectively. As a group, they are often referred to as the silver halides, and are often given the pseudo-chemical notation AgX. Although most silver halides involve silver atoms with oxidation states of +1 (Ag), silver halides in which the silver atoms have oxidation states of