 The three Group 4 elements that occur naturally are titanium ( Ti ) , zirconium ( Zr ) and hafnium ( Hf ) . The first three members of the group share similar properties ; all three are hard refractory metals under standard conditions . However , the fourth element rutherfordium ( Rf ) , has been synthesized in the laboratory ; none of its isotopes have been found occurring in nature . All isotopes of rutherfordium are radioactive . So far , no experiments in a <unk> have been conducted to synthesize the next member of the group , <unk> ( <unk> ) , and it is unlikely that they will be synthesized in the near future . 
