 Most of the chemistry has been observed only for the first three members of the group . The chemistry of rutherfordium is not very established and therefore the rest of the section deals only with titanium , zirconium , and hafnium . All the elements of the group are reactive metals with a high melting point ( 1668 ° C , 1855 ° C , 2233 ° C , 2100 ° C ? ) . The reactivity is not always obvious due to the rapid formation of a stable oxide layer , which prevents further reactions . The oxides TiO2 , ZrO2 and HfO2 are white solids with high melting points and unreactive against most acids . 
