Chemical element
species of atoms having the same number of protons in the atomic nucleus and the same chemical properties, but not nessarily the same mass, or the same stability (or half-lifetime if they are unstable)
zirconium
group 16
niobium
molybdenum
technetium
heavy metal
ruthenium
rhodium
palladium
silver
cadmium
indium
tin
uranium
antimony
tellurium
plutonium
iodine
neptunium
xenon
cesium
protactinium
barium
thorium
hafnium
actinium
tantalum
radium
radon
rutherfordium
dubnium
seaborgium
bohrium
hassium
meitnerium
darmstadtium
roentgenium
copernicium
hypothetical chemical element
flerovium
livermorium
cerium
praseodymium
neodymium
europium
thorium-230
incompatible element
lanthanum
promethium
samarium