Element Barium, Ba, Alkaline Earth Metal. Has the combining weight 137. 4, and occurs naturally as sulphate and carbonate. Metallic barium is of a white colour, melts at a red heat, and reacts more energetically with water than strontium or calcium. We have here, therefore, a repetition of the same state of affairs as in the group of alkali metals, viz. the action with oxygen and oxygen compounds is more energetic the higher the combining weight of the metal. Barium forms only the divalent ion Ba.

Element Radium, Ra, Alkaline Earth Metal. Isotopes may be found in nature. It becomes possible because of existence of three radioactive series in which radium isotopes.

Element Samarium, Sm, Lanthanide. Samarium is one of the less common of the rare earth elements, being on the one hand much less abundant than the other elements of the cerium group, and on the other hand much more abundant than europium, terbium, and thulium. It is about as plentiful as gadolinium. Samarium is a yellow metal of density 7. The metal quickly tarnishes in the air. Extracted by Mosander from ceria earth. The samarskite mineral was named.

Element Thorium, Th, Actinide or Actinoid. It was done by Lars Frederik Nilson in 1882. Is a member of actinide. Isotope is the most long-lived and is found in nature. Are known, the most important of which are thorite Th.

Element Hafnium, Hf, Transition Metal. In 1911 Urbain noticed several new lines in spectrum of the fractions of yttria mother solution and, thinking he had found a new element similar to the rare earths, called it celtium.

Element Lanthanum, La, Lanthanide. Lanthanum is a tin-white metal of density 6. It is malleable, but not ductile. Measurements made with material of doubtful purity indicate that lanthanum is feebly paramagnetic, but this is questionable. 923 and its heat of formation 97. it resembles the corresponding cerium compound.