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The nomenclature 'selenium' originates from the Greek word for the moon ('selene'), a naming convention chosen by its discoverer, Jöns Jacob Berzelius.
Answer: True
Jöns Jacob Berzelius discovered selenium in 1817 and named it after 'selene,' the Greek word for the moon, due to its perceived similarity to tellurium, which was named after the Earth.
Selenium is abundant in nature, frequently found in its pure elemental state or as distinct selenium ores.
Answer: False
Selenium is relatively rare in the Earth's crust and seldom occurs in its pure elemental state or as distinct selenium ores. It is most commonly found as an impurity within metal sulfide ores, substituting for sulfur.
The gray, hexagonal allotrope of selenium is the most stable and possesses a dense, crystalline structure.
Answer: True
The gray, hexagonal form of selenium is its most stable allotrope, characterized by a dense crystalline structure composed of helical polymeric chains.
Gray selenium is characterized by its high solubility in carbon disulfide and its susceptibility to oxidation.
Answer: False
Gray selenium is insoluble in carbon disulfide and is notably resistant to oxidation by air and non-oxidizing acids, distinguishing it from other allotropes.
All seven naturally occurring isotopes of selenium are radioactive with very short half-lives.
Answer: False
Selenium has seven naturally occurring isotopes, five of which are stable (74Se, 76Se, 77Se, 78Se, 80Se). The isotope 82Se is a primordial radionuclide with a very long half-life, and 79Se is a fission product with a long half-life.
The most stable synthetic isotope of selenium, 75Se, has a half-life measured in hours.
Answer: False
The most stable synthetic isotope, 75Se, has a half-life of approximately 119.78 days, not hours. Other synthetic isotopes like 72Se have half-lives measured in days.
What is the atomic number and symbol for selenium?
Answer: Atomic number 34, Symbol Se
Selenium is a chemical element with the atomic number 34 and is represented by the symbol Se.
Who discovered selenium and in what year?
Answer: Jöns Jacob Berzelius in 1817
Selenium was discovered by the Swedish chemist Jöns Jacob Berzelius in 1817.
Where is selenium most commonly found in its natural state?
Answer: As an impurity within metal sulfide ores, substituting for sulfur
Selenium is rarely found in its pure elemental form or as distinct ores. It is most commonly encountered as a trace impurity within metal sulfide ores, where it substitutes for sulfur atoms in the crystal lattice.
Which allotrope of selenium is the most stable and has a dense, hexagonal crystal structure?
Answer: Gray hexagonal form
The gray, hexagonal form of selenium is its most stable allotrope, characterized by a dense crystalline structure composed of helical polymeric chains.
In its chemical compounds, selenium typically exhibits oxidation states of -1, +3, and +5.
Answer: False
Selenium commonly exhibits oxidation states of -2, +4, and +6 in its compounds. The states -1 and +3 are less typical or observed under specific conditions, and +5 is not a common oxidation state for selenium.
Selenium dioxide (SeO2) is produced when elemental selenium burns in the presence of oxygen.
Answer: True
Selenium dioxide (SeO2) is formed through the direct combustion of elemental selenium in an oxygen atmosphere.
Selenous acid is prepared by dissolving selenium trioxide in water.
Answer: False
Selenous acid (H2SeO3) is formed when selenium dioxide (SeO2) dissolves in water. Selenium trioxide (SeO3) is less stable and reacts differently.
Selenium hexafluoride (SeF6) is less hazardous and less reactive than its sulfur analogue, sulfur hexafluoride (SF6).
Answer: False
Selenium hexafluoride (SeF6) is generally considered more reactive and a greater pulmonary irritant compared to sulfur hexafluoride (SF6).
Hydrogen selenide (H2Se) is a stable, non-toxic gas similar in properties to hydrogen sulfide.
Answer: False
Hydrogen selenide (H2Se) is a highly toxic and unstable gas, although it shares structural similarities with hydrogen sulfide (H2S).
Tetraselenium tetranitride (Se4N4) is a stable, non-explosive compound used in fertilizers.
Answer: False
Tetraselenium tetranitride (Se4N4) is an explosive compound, analogous to tetrasulfur tetranitride, and is not used in fertilizers.
Organoselenium compounds, like selenides and selenols, are structurally analogous to organosulfur compounds.
Answer: True
Organoselenium compounds, including selenides (R2Se), diselenides (R2Se2), and selenols (RSeH), exhibit structural similarities to their organosulfur counterparts, reflecting selenium's position in the same group as sulfur in the periodic table.
Which of the following is NOT a common oxidation state of selenium?
Answer: +5
The common oxidation states for selenium in its compounds are -2, +4, and +6. The oxidation state +5 is not typically observed for selenium.
Which of the following is an example of a metal selenide semiconductor mentioned in the source?
Answer: Zinc Selenide (ZnSe)
Zinc selenide (ZnSe) is cited as an example of a metal selenide compound that functions as a semiconductor.
Which of the following is an example of an organoselenium compound?
Answer: Selenomethionine
Selenomethionine is an amino acid that incorporates selenium, making it a key example of an organoselenium compound found in biological systems.
Selenium, atomic number 34, is primarily recognized for its role as a constituent in structural alloys, enhancing properties such as machinability.
Answer: False
While selenium can be incorporated into certain alloys, such as brass, to enhance machinability, it is not primarily known as a structural metal itself. Its applications are more diverse, including glass production and semiconductor technology.
A significant industrial application of selenium involves its use as a decolorizing agent and colorant in glass production.
Answer: True
Selenium is widely employed in the glass industry to neutralize the green tint caused by iron impurities, acting as a decolorizer, and also to impart a desirable red color to glass.
Willoughby Smith's 1873 discovery demonstrated that selenium's electrical conductivity is unaffected by light.
Answer: False
Willoughby Smith's seminal 1873 discovery revealed that the electrical conductivity of selenium is significantly affected by light, a phenomenon known as photoconductivity, which paved the way for its use in light-sensing devices.
Selenium rectifiers were an early application of its semiconductor properties, eventually superseded by silicon devices.
Answer: True
Selenium rectifiers, developed in the early 20th century, were an important early application leveraging selenium's semiconductor properties for converting alternating current to direct current. They were eventually replaced by more efficient silicon-based devices.
Selenium is primarily extracted from crude oil refining processes.
Answer: False
Selenium is not primarily extracted from crude oil refining. Its main industrial source is as a byproduct of copper electrolytic refining, where it is recovered from anode slimes.
The production of elemental selenium involves oxidizing copper refinery residues to form selenium dioxide, then reducing it.
Answer: True
Elemental selenium is typically produced by processing copper refinery residues. This involves oxidizing the selenium-containing materials to form selenium dioxide, which is then further processed and reduced to elemental selenium.
The largest commercial use of selenium today is in the manufacturing of semiconductors for microchips.
Answer: False
The largest commercial use of selenium is in the glass industry (approximately 50% of consumption) for decolorizing and coloring. While it is used in semiconductors, this is not its largest application.
Adding selenium to brass alloys can improve machinability and serve as a lead replacement.
Answer: True
Selenium is incorporated into brass alloys, often alongside bismuth, to enhance machinability and provide an alternative to lead, particularly in applications related to potable water systems.
Amorphous selenium films are utilized in modern flat-panel X-ray detectors for their photoconductive properties.
Answer: True
Amorphous selenium thin films are key components in flat-panel X-ray detectors, functioning as photoconductors that convert X-ray photons directly into electrical signals, enabling high-resolution medical imaging.
Selenium's role in X-ray crystallography is primarily as a source of radiation for imaging.
Answer: False
In X-ray crystallography, selenium is incorporated into molecules (often replacing sulfur) to aid in phasing techniques, such as MAD and SAD, which are essential for determining the three-dimensional structure of proteins and other macromolecules. It is not used as a radiation source.
In photography, selenium is used in print toning to enhance image permanence and tonal range.
Answer: True
Selenium toning is a photographic process used to enhance the archival permanence and modify the tonal characteristics of black-and-white prints, often imparting a warmer tone.
A major challenge for selenium solar cells is achieving a high open-circuit voltage.
Answer: False
A primary challenge in enhancing the efficiency of selenium solar cells is overcoming a deficit in open-circuit voltage, rather than achieving a high one. Research focuses on improving carrier lifetime and reducing recombination.
Which of the following is a primary industrial application of selenium?
Answer: Use as a semiconductor in photocells and electronic devices
Key industrial applications of selenium include its use as a semiconductor material in photocells, light meters, and other electronic devices, as well as its role in glass manufacturing and pigment production.
What property of gray selenium, discovered in 1873, led to its technological applications?
Answer: Its photoconductivity (electrical conductivity affected by light)
The discovery in 1873 that gray selenium exhibits photoconductivity—meaning its electrical conductivity changes with light intensity—was pivotal, leading to its application in light-sensing devices like photocells.
How is selenium primarily obtained industrially?
Answer: As a byproduct of copper electrolytic refining
The principal industrial source of selenium is as a byproduct recovered during the electrolytic refining of copper, where it accumulates in the anode slimes.
What is the main reason selenium is added to glass?
Answer: To act as a decolorizer and impart a red color
Selenium is added to glass primarily to neutralize unwanted greenish tints caused by iron impurities (decolorizing) and to impart a distinct red color, widely used for decorative glass and signal lenses.
How is selenium used in photography?
Answer: In print toning to enhance permanence and tonal range
In traditional black-and-white photography, selenium is employed in print toning processes to improve the longevity of prints and to subtly alter their tonal range, often yielding warmer hues.
Selenium rectifiers were historically important for what purpose?
Answer: Converting AC to DC current
Selenium rectifiers were crucial early semiconductor devices used primarily for converting alternating current (AC) to direct current (DC) in electronic power supplies.
What is a challenge in improving the efficiency of selenium solar cells?
Answer: Deficit in open-circuit voltage
A primary challenge in enhancing the efficiency of selenium solar cells is overcoming a deficit in open-circuit voltage. Research focuses on defect engineering to improve carrier lifetime and mitigate recombination losses.
How are amorphous selenium thin films used in X-ray detection?
Answer: As photoconductors converting X-rays directly to electric charge
Amorphous selenium thin films function as photoconductors in flat-panel X-ray detectors, directly converting incident X-ray photons into electrical charge carriers, which are then read out to form an image.
Selenium is toxic in all forms and concentrations, making it unsuitable for biological functions.
Answer: False
While selenium can be toxic in excessive amounts, trace quantities are essential for numerous biological functions, particularly as a component of antioxidant enzymes. Its toxicity is highly dependent on the form and dose.
Selenium is not biologically essential and plays no role in human cellular function.
Answer: False
Selenium is an essential trace element for humans and many animals. It is a critical component of various enzymes, including antioxidant enzymes and those involved in thyroid hormone metabolism.
Selenium deficiency is common globally and can lead to severe neurological disorders even without other stressors.
Answer: False
Pure selenium deficiency is relatively rare globally. While it can exacerbate other health issues or contribute to conditions like Kashin-Beck disease under specific circumstances, it does not typically lead to severe neurological disorders in isolation without other contributing factors.
A garlic odor on the breath is one of the milder symptoms of selenium toxicity (selenosis).
Answer: False
A garlic odor on the breath is indeed a symptom of selenium toxicity (selenosis), but it is often accompanied by other significant symptoms such as hair loss, nail changes, and gastrointestinal distress, indicating a potentially serious condition rather than a mild one.
High selenium intake can exacerbate mercury toxicity by interfering with essential enzymes.
Answer: False
Conversely, increased dietary selenium intake has been shown to help mitigate the effects of mercury toxicity, particularly at moderate exposure levels, by forming complexes with mercury and potentially supporting cellular defense mechanisms.
Brazil nuts are an exceptionally rich source of selenium, significantly more so than common meats or cereals.
Answer: True
Brazil nuts are renowned for their exceptionally high selenium content, often exceeding that found in common dietary sources like meats and cereals, though the exact amount can vary based on soil conditions.
The Recommended Dietary Allowance (RDA) for selenium for adults is 550 micrograms per day.
Answer: False
The Recommended Dietary Allowance (RDA) for selenium for adults in the United States is 55 micrograms (μg) per day, not 550 micrograms.
Selenium is crucial for thyroid hormone metabolism as it is a component of the hormones themselves.
Answer: False
Selenium is crucial for thyroid hormone metabolism, but not as a component of the hormones themselves. It acts as a cofactor for deiodinase enzymes, which are responsible for activating and deactivating thyroid hormones.
Selenocysteine and selenomethionine are common organoselenium compounds found in living systems, mimicking sulfur's role.
Answer: True
Selenocysteine and selenomethionine are key organoselenium compounds found in biological systems, where they function analogously to their sulfur-containing counterparts (cysteine and methionine) within proteins.
The discovery of selenocysteine revealed that the UGA codon can specify an amino acid instead of termination.
Answer: True
The identification of selenocysteine as a component of certain proteins was significant because it demonstrated that the UGA codon, typically recognized as a stop signal, can instead specify the incorporation of an amino acid during protein synthesis.
Selenium and iodine have independent roles in thyroid health, with no significant interaction.
Answer: False
Selenium and iodine have closely intertwined roles in thyroid health. Iodine is essential for the synthesis of thyroid hormones, while selenium is a crucial cofactor for the deiodinase enzymes that regulate the activation and inactivation of these hormones.
The Tolerable Upper Intake Level (UL) for selenium for adults is 400 micrograms per day, and exceeding it can cause selenosis.
Answer: True
The Tolerable Upper Intake Level (UL) for selenium for adults is established at 400 micrograms (μg) per day. Consistently exceeding this limit can lead to selenosis, a condition characterized by various toxic effects.
Elemental selenium and metallic selenides are highly toxic due to their rapid absorption and bioavailability.
Answer: False
Elemental selenium and metallic selenides generally exhibit lower toxicity compared to more bioavailable forms like selenates and selenites, due to their slower absorption rates. High bioavailability correlates with increased toxicity.
Measuring selenium levels in blood or urine is used for monitoring exposure and diagnosing poisoning.
Answer: True
Biomonitoring of selenium levels in biological samples, such as blood, plasma, serum, or urine, is a standard practice for assessing occupational or environmental exposure and for diagnosing potential selenium toxicity.
Selenium's role in the immune system is primarily related to its ability to form structural components of antibodies.
Answer: False
Selenium's contribution to the immune system is primarily linked to its antioxidant functions via selenoproteins, which help protect immune cells from oxidative stress and modulate immune responses, rather than forming structural components of antibodies.
What is the biological significance of selenium?
Answer: Trace amounts are essential for cellular function as a component of enzymes.
Trace amounts of selenium are biologically essential for humans and other animals, serving as a critical cofactor for various antioxidant enzymes, such as glutathione peroxidase and thioredoxin reductase, which protect cells from oxidative damage.
Which of the following is a common symptom of selenium toxicity (selenosis)?
Answer: Garlic odor on breath and nail changes
Common symptoms associated with selenium toxicity (selenosis) include a characteristic garlic odor on the breath, hair loss, nail deformities, gastrointestinal disturbances, and neurological effects.
What is the role of selenium in thyroid hormone metabolism?
Answer: It activates thyroid hormones via deiodinase enzymes.
Selenium is a vital cofactor for thyroid hormone deiodinase enzymes, which regulate the conversion of the prohormone thyroxine (T4) to the active hormone triiodothyronine (T3) and also facilitate the deactivation of thyroid hormones.
How does selenium's bioavailability influence its toxicity?
Answer: Highly bioavailable forms like selenates and selenites are much more toxic than elemental selenium.
Selenium's toxicity is strongly influenced by its bioavailability. Highly bioavailable forms, such as selenates and selenites, are significantly more toxic than elemental selenium or metallic selenides, which are absorbed more slowly.
What is the primary function of selenium in the human body?
Answer: Acting as a cofactor for antioxidant enzymes
The primary function of selenium in the human body is as a cofactor for antioxidant enzymes, such as glutathione peroxidase and thioredoxin reductase, which play a critical role in protecting cells from oxidative damage.
What is the significance of selenocysteine in protein synthesis?
Answer: It is incorporated using the UGA codon, normally a stop signal.
Selenocysteine is unique in that its incorporation into proteins during translation occurs via the UGA codon, which is typically recognized as a stop signal. This process requires specific mRNA structures and translation factors.
What is the Tolerable Upper Intake Level (UL) for selenium for adults?
Answer: 400 micrograms (μg) per day
The Tolerable Upper Intake Level (UL) for selenium for adults is established at 400 micrograms (μg) per day. Exceeding this level increases the risk of adverse health effects.
What is the relationship between selenium and mercury toxicity?
Answer: Selenium can help mitigate the effects of mercury toxicity.
Adequate selenium intake can help mitigate mercury toxicity. Selenium can bind to mercury, forming less toxic complexes, and may support cellular defense mechanisms against mercury's harmful effects.
Which of the following is a common dietary source of selenium?
Answer: Brazil nuts
Common dietary sources of selenium include meats, cereals, and nuts. Brazil nuts are particularly notable for their exceptionally high selenium content.
Selenium pollution in aquatic ecosystems can lead to bioaccumulation and cause deformities in fish and waterbirds.
Answer: True
Selenium pollution, often originating from agricultural runoff or industrial discharge, can bioaccumulate in aquatic environments, leading to severe health issues and developmental deformities in fish and waterbirds.
The Kesterson National Wildlife Refuge incident involved selenium poisoning of fish and waterbirds due to agricultural runoff.
Answer: True
The Kesterson National Wildlife Refuge in California experienced a significant environmental crisis due to selenium poisoning, primarily caused by agricultural irrigation drainage water concentrating selenium and harming aquatic life and waterbirds.
According to GHS classification, selenium is considered safe for consumption and poses no risk to aquatic life.
Answer: False
The Globally Harmonized System (GHS) classifies selenium as toxic if swallowed or inhaled, suspected of damaging fertility or the unborn child, and causing organ damage through prolonged exposure. It also carries warnings regarding long-lasting harmful effects on aquatic life.
The NFPA 704 rating for selenium indicates a high flammability hazard and significant instability.
Answer: False
The NFPA 704 rating for selenium indicates a health hazard of 2, flammability of 0 (will not burn), and instability of 0 (normally stable). It does not signify high flammability or significant instability.
Some plant species, known as selenium indicators, accumulate selenium and thrive in selenium-rich soils.
Answer: True
Certain plant species, termed selenium indicators, possess the ability to thrive in soils with high selenium concentrations and actively accumulate the element, sometimes as a defense mechanism.
OSHA has set the permissible exposure limit (PEL) for selenium in the workplace at 2.0 mg/m³.
Answer: False
The Occupational Safety and Health Administration (OSHA) has set the permissible exposure limit (PEL) for selenium in the workplace at 0.2 mg/m³ over an 8-hour time-weighted average.
What hazard does the GHS classification associate with selenium regarding fertility?
Answer: Suspected of damaging fertility or the unborn child
According to the Globally Harmonized System (GHS) classification, selenium is categorized as 'Suspected of damaging fertility or the unborn child' (H361).
What is a major environmental concern related to selenium pollution?
Answer: Bioaccumulation in aquatic organisms leading to deformities
A significant environmental concern with selenium pollution is its tendency to bioaccumulate in aquatic food webs, leading to elevated concentrations in organisms and causing developmental abnormalities and reproductive issues in fish and waterbirds.
What does the NFPA 704 rating indicate for selenium's flammability?
Answer: 0 (Will not burn)
The NFPA 704 rating for selenium indicates a flammability hazard of 0, signifying that it will not burn under normal fire conditions.