The element with 48 protons is Cadmium (Cd). Its atomic number, 48, uniquely defines its position on the periodic table. Cadmium is a naturally occurring metal, but its use in human applications has significantly increased its environmental presence. This overview covers its structure, physical nature, industrial uses, and serious biological impact.
Cadmium’s Place on the Periodic Table
Cadmium holds the 48th position on the periodic table, located in Group 12, Period 5, directly beneath zinc. This placement means it shares chemical similarities with zinc and mercury. Its average atomic weight is approximately 112.414 atomic mass units (amu). The atomic structure includes 48 protons and 48 electrons, with the electron configuration [Kr]4d105s2. Cadmium exists as a mixture of eight naturally occurring isotopes, with Cadmium-114 (114Cd) being the most abundant. It is primarily recovered as a minor byproduct during the mining and refining of zinc ores.
Defining Physical and Chemical Characteristics
Cadmium is a soft, silvery-white metal, often displaying a slight bluish-gray tint. It is both malleable and ductile, and it has a relatively low melting point for a metal, around 321°C (610°F). Chemically, Cadmium strongly prefers a +2 oxidation state in nearly all its compounds. It is resistant to corrosion, a property that makes it valuable for protective coatings. The element is typically sourced from the processing of zinc, lead, and copper ores, where it exists as an impurity in the zinc mineral sphalerite.
Essential Industrial and Commercial Uses
Cadmium is used in several important industrial applications.
Batteries
Historically, its most significant use has been in rechargeable nickel-cadmium (NiCd) batteries. These batteries are known for their long cycle life and reliable performance in devices like cordless tools. However, their use is being restricted in some regions due to toxicity concerns.
Electroplating
The metal is highly valued for electroplating, where a thin layer is applied to metals, particularly steel, to provide excellent corrosion resistance. This application is prevalent in the aerospace and military industries for components exposed to marine or high-salt environments.
Pigments
Cadmium compounds are also used to create brilliant, long-lasting pigments in plastics and paints, producing vibrant yellow, orange, and red colors. These pigments are indispensable in certain high-temperature processing applications and for artists’ materials.
Biological Impact and Toxicity
Despite its industrial utility, Cadmium is a highly toxic heavy metal with no known beneficial function in the human body. It is a cumulative toxin because the body has a limited ability to excrete it, leading to a continuous increase in the body burden over a lifetime. Cadmium has an extremely long biological half-life, estimated to range from 16 to 30 years, allowing it to accumulate in tissues.
Exposure pathways include inhalation (primarily cigarette smoke, as tobacco plants accumulate Cadmium) and ingestion of contaminated food and water (taken up by plants from the soil and concentrated in shellfish and crops).
Once absorbed, Cadmium is transported to the liver and then to the kidneys, which are the most significantly impacted organs. Accumulation in the renal cortex causes severe kidney damage, leading to impaired function and increased protein excretion. Long-term exposure is also associated with chronic lung diseases, such as emphysema. Furthermore, Cadmium interferes with calcium metabolism, leading to bone demineralization and increasing the risk of osteoporosis and bone fractures. The metal is classified as a carcinogen, linked to an elevated risk of various cancers, including those of the lung, prostate, and kidney.