Introduction
Cadmium is a transition metal present in group number 12 and d – block of the periodic table.
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- Its atomic number is 48 and its atomic mass is 112.41.
- Cadmium has 48 electrons.
- It has 48 protons and 66 neutrons in its nucleus.
- Cadmium is represented by the symbol “Cd”.
Naming and History
The name cadmium is derived from the Latin word “Cadmia” and the Greek word “Kadmeia”. These both words are ancient names of Calamine (Calamine is zinc carbonate).
- Apothecaries
Apothecaries of Hanover, Germany in the early 1800s, produced zinc oxide from naturally occurring zinc carbonate which they called cadmia.
- Friedrich Stromeyer
In 1817, German chemist Friedrich Stromeyer discovered zinc carbonate or cadmium as an impurity in zinc oxide. He knew that heating zinc carbonate would convert into oxide white in color. He heated zinc carbonate and instead of white, it converted to yellowish oxide.
He thought this would be due to contaminations of iron or lead but he did not find any of these metals. He decided to further study and analyze it. He observed that this color was due to previously unknown metal. He extracted this metal carefully from the oxide.
He isolated it and was the first who produced cadmium metal. He named it after cadmia, an old name for calamine – the zinc ore. He also analyzed other zin compounds; the new metal was present in them. Even it was present in trace amounts in pure zinc.
- Karl Hermann
In 1818, another German chemist, Karl Hermann independently discovered cadmium. He observed yellowish color in zinc sulphide. He assumed it was the contamination of arsenic. But on further research, he found that it was a new element.
Occurrence of Cadmium
Cadmium is mainly present in Earth’s crust. It always occurs in a combined form with zinc. It is mainly extracted as the by-product of zinc, copper, and lead. Some cadmium is also present in rivers through weathering of rocks.
Air also contains cadmium, which is released through the burning of fossils and volcanic eruptions. It is present in zinc ores. Greenockite – a CdS mineral is a source of cadmium. No ores are especially mined for cadmium because enough quantities are produced as a by-product.
The major suppliers of cadmium are Canada, Australia, Mexico, Japan, and Peru.
Properties of Cadmium
Cadmium is bluish-white and silver, lustrous, soft, malleable, and ductile transition metal. It is soft that can be cut with a knife. It tarnishes in the air. When burning in air, produces cadmium oxide in brown color.
It is a good conductor of electricity and is resistant to corrosion. Cadmium is soluble in acids but not dissolved by alkalies. It has a striking resemblance in chemical and physical properties with zinc.
The melting point of cadmium is 321.07 ᵒC and its boiling point is 767 ᵒC. It has a density of 8.69 grams per cubic meter. It exists as solid at room temperature.
Cadmium in Biological Systems
Cadmium is considered highly toxic. It is carcinogenic (cancer-causing) and teratogenic (mutations in embryos or fetus). On ingestion of cadmium, it can cause vomiting, nausea, diarrhea, headaches.
It can also cause heart and liver diseases.
Uses of Cadmium
- Most cadmium (around 80%) today is used in rechargeable nickel–cadmium batteries.
- It is also used in pigments such as cadmium sulphide in yellow pigment, paints, coatings, etc.
- Its property of absorbing neutrons makes it valuable in using nuclear reactors.
- It is used as a stabilizer for plastics and in electroplating steel especially for protection in the sea.
- It is alloyed with silver to make solder which is used in joining metallic items and electronic components.
- It is used in green and black phosphor in color television tubes.
Isotopes of Cadmium
There are around 34 isotopes of cadmium from mass numbers ranging from 97 to 130. There are 8 naturally occurring stable isotopes of cadmium. The most abundant isotope is Cd – 114 with 28.7 % abundance.
Multiple Choice Questions (MCQs) – Cadmium
- What is the atomic number of cadmium?
- A) 12
- B) 48
- C) 66
- D) 112.41
- Cadmium belongs to which group in the periodic table?
- A) Group 1
- B) Group 12
- C) Group 18
- D) Group 5
- Who discovered cadmium and named it after the old name for calamine?
- A) Karl Hermann
- B) Friedrich Stromeyer
- C) William Ramsay
- D) Morris Travers
- What is the symbol for cadmium?
- A) Zn
- B) Ca
- C) Cd
- D) Ce
- Cadmium is often found in combination with which element?
- A) Iron
- B) Zinc
- C) Copper
- D) Lead
- In what form is cadmium mainly extracted?
- A) Pure form
- B) Alloy form
- C) Combined form with zinc
- D) Oxide form
- What is the color of cadmium oxide produced when burning in air?
- A) White
- B) Brown
- C) Green
- D) Blue
- Which mineral is a source of cadmium?
- A) Hematite
- B) Greenockite
- C) Galena
- D) Chalcopyrite
- What is the melting point of cadmium?
- A) 141.07 ᵒC
- B) 321.07 ᵒC
- C) 567 ᵒC
- D) 767 ᵒC
- Cadmium is resistant to corrosion and has a striking resemblance to the properties of which metal?
- A) Copper
- B) Gold
- C) Zinc
- D) Iron
- Why is cadmium considered highly toxic?
- A) It causes hair loss
- B) It is a carcinogen
- C) It enhances memory
- D) It promotes cell growth
- What is the major use of cadmium in today’s applications?
- A) Paints
- B) Batteries
- C) Nuclear reactors
- D) Electronic components
- In which industry is cadmium used as a stabilizer for plastics?
- A) Automotive
- B) Aerospace
- C) Healthcare
- D) Construction
- What is the primary use of cadmium in the production of green and black phosphor?
- A) Cosmetics
- B) Food coloring
- C) Television tubes
- D) Medicinal drugs
- How many stable isotopes does cadmium have?
- A) 5
- B) 8
- C) 15
- D) 34
- Which isotopic form of cadmium is the most abundant?
- A) Cd-114
- B) Cd-97
- C) Cd-130
- D) Cd-66
- What is the abundance percentage of Cd-114?
- A) 12.3%
- B) 28.7%
- C) 55.4%
- D) 89.2%
- Cadmium is alloyed with silver to produce:
- A) Gold
- B) Platinum
- C) Solder
- D) Nickel
- What is the primary color associated with cadmium sulfide in pigments?
- A) Red
- B) Yellow
- C) Blue
- D) Green
- How does cadmium enter the air?
- A) Through photosynthesis
- B) Volcanic eruptions
- C) Ocean currents
- D) Earthquakes
- In what form does cadmium exist at room temperature?
- A) Gas
- B) Liquid
- C) Solid
- D) Plasma
- Which two chemists independently discovered cadmium in 1818?
- A) William Ramsay and Morris Travers
- B) Friedrich Stromeyer and Karl Hermann
- C) Dmitri Mendeleev and Antoine Lavoisier
- D) Linus Pauling and Marie Curie
- The name “Cadmium” is derived from the ancient names of:
- A) Copper and Aluminum
- B) Zinc and Calamine
- C) Iron and Lead
- D) Gold and Silver
Answers:
- B) 48
- B) Group 12
- B) Friedrich Stromeyer
- C) Cd
- B) Zinc
- C) Combined form with zinc
- B) Brown
- B) Greenockite
- B) 321.07 ᵒC
- C) Zinc
- B) It is a carcinogen
- B) Batteries
- A) Automotive
- C) Television tubes
- B) 8
- A) Cd-114
- B) 28.7%
- C) Solder
- B) Yellow
- B) Volcanic eruptions
- C) Solid
- B) Friedrich Stromeyer and Karl Hermann
- B) Zinc and Calamine
Summary: Cadmium – Occurrence, Properties, Uses, and Isotopes
Cadmium, a transition metal found in group 12 of the periodic table, is characterized by its atomic number of 48 and atomic mass of 112.41. Represented by the symbol “Cd,” it possesses 48 electrons, 48 protons, and 66 neutrons. The name “cadmium” is derived from the Latin word “Cadmia” and the Greek word “Kadmeia,” ancient names for Calamine (zinc carbonate). Discovered independently by Friedrich Stromeyer and Karl Hermann in the early 19th century, cadmium occurs mainly in Earth’s crust, commonly associated with zinc.
Cadmium’s properties include a bluish-white and silver appearance, softness allowing it to be cut with a knife, and susceptibility to tarnishing in air. It is a good conductor of electricity, resistant to corrosion, and shares similarities with zinc in chemical and physical properties. Major suppliers include Canada, Australia, Mexico, Japan, and Peru.
Despite its industrial uses, cadmium is highly toxic, exhibiting carcinogenic and teratogenic effects. In biological systems, ingestion can lead to symptoms such as vomiting, nausea, diarrhea, headaches, and more severe conditions affecting the heart and liver.
Cadmium finds applications in various industries, with approximately 80% used in rechargeable nickel–cadmium batteries. It is also utilized in pigments, nuclear reactors, plastics stabilization, electroplating, solder production, and phosphors for color television tubes.
Cadmium possesses a range of isotopes, with 34 isotopes identified. Among its eight naturally occurring stable isotopes, Cd-114 is the most abundant, constituting 28.7% of cadmium isotopes. The element’s versatility and significance in industrial applications underscore the need for understanding its properties and potential hazards.