The fourteen elements which follow actinium from thorium (Z=90) to lawrencium (Z=103) are called actinoids. They involve the filling of 5f− subshell. Californium (Cf) has the atomic number 98 and its configuration is as Cf(Z=98):[Rn]5f10,6d0,7s2 Hence, it is a member of actinide series.