Introduction to Gadolinium (Gd)
Gadolinium, designated by the chemical symbol Gd, is an element with atomic number 64. It belongs to the lanthanide series, which is a group of rare-earth elements found in Group 3, Period 6 of the periodic table. It is a silvery-white, malleable, and ductile metal. Gadolinium exhibits unique magnetic properties, becoming strongly ferromagnetic at room temperature, a characteristic shared by only a few other elements like iron, nickel, and cobalt.
General Properties
Gadolinium is a moderately soft metal that tarnishes in moist air, forming an oxide coating. Its melting point is approximately 1312 °C, and its boiling point is around 3273 °C. Like other lanthanides, gadolinium typically exists in the +3 oxidation state in its compounds.
Chemical Reactivity
Gadolinium is a reactive metal, though less reactive than alkali metals and alkaline earth metals. Its reactivity is characteristic of other lanthanides.
Reaction with Water
Gadolinium reacts slowly with cold water, forming gadolinium hydroxide and hydrogen gas. The reaction becomes more vigorous with hot water. The chemical equation representing its reaction with water is: $2\text{Gd(s)} + 6\text{H}_2\text{O(l)} \rightarrow 2\text{Gd(OH)}_3\text{(aq)} + 3\text{H}_2\text{(g)}$
Reaction with Air
In dry air, gadolinium tarnishes slowly, forming a protective layer of gadolinium(III) oxide. When heated in air or oxygen, it readily burns to form gadolinium(III) oxide. $4\text{Gd(s)} + 3\text{O}_2\text{(g)} \rightarrow 2\text{Gd}_2\text{O}_3\text{(s)}$
Reaction with Acids
Gadolinium reacts readily with most dilute acids to form gadolinium(III) salts and hydrogen gas. For example, with hydrochloric acid: $2\text{Gd(s)} + 6\text{HCl(aq)} \rightarrow 2\text{GdCl}_3\text{(aq)} + 3\text{H}_2\text{(g)}$
Health and Safety Aspects
Understanding the health and safety implications of chemical elements is crucial.
Toxicity
Gadolinium metal itself is considered to have low acute toxicity. However, gadolinium ions (Gd³⁺), particularly when not bound to chelating agents, can be toxic if they accumulate in the body. Certain gadolinium-based contrast agents used in Magnetic Resonance Imaging (MRI) have shown tendencies to deposit in various tissues, including the brain, in some individuals, leading to ongoing research and medical scrutiny. These contrast agents typically involve gadolinium ions chelated by organic ligands to reduce their toxicity and facilitate their excretion from the body. Such MRI procedures are commonly performed in hospitals across India.
Radioactivity
Naturally occurring gadolinium is not radioactive. It consists of a mixture of several stable isotopes (e.g., ¹⁵⁴Gd, ¹⁵⁵Gd, ¹⁵⁶Gd, ¹⁵⁷Gd, ¹⁵⁸Gd, ¹⁶⁰Gd) and two very long-lived, weakly radioactive isotopes (¹⁵²Gd and ¹⁵⁰Gd) with half-lives orders of magnitude longer than the age of the universe. For practical purposes, natural gadolinium is considered non-radioactive. Synthetic radioactive isotopes of gadolinium can be produced, but these are not naturally occurring.
Flammability
In its bulk metallic form, gadolinium is not considered highly flammable under normal conditions, but it will burn at elevated temperatures in air. As with many metals, finely divided gadolinium powder can be highly flammable and potentially explosive when dispersed in air, reacting vigorously with oxygen.
Notable Chemical Reaction
The formation of gadolinium oxide is a fundamental and common chemical reaction for gadolinium, demonstrating its reactivity with oxygen. This reaction is significant because gadolinium oxide (Gd₂O₃) is an important compound used in various applications, including phosphors for televisions and X-ray intensifying screens. Gadolinium itself, along with other rare earth elements, is extracted from minerals like monazite sands found in coastal regions of India, such as Kerala, where these elements are chemically processed into their oxide forms.