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Protactinium is one of the rarest elements on the Earth. It is formerly known as protoactinium with the symbol ‘Pa’ and atomic number 91. Protactinium has a very bright metallic lustre that lasts for a long time when exposed to air.
- Below 1.4 K, Protactinium acts as a superconductive.
- It quickly reacts with oxygen, water vapour, and inorganic acids.
- When the uranium and other radioactive elements decay, it produces this substance.
- The radioactive chemical element belongs to the actinoid series of the periodic table
- The element is an alpha-emitter and, like polonium, is a radiological threat.
- Protactinium is a member of the actinide family of elements in the periodic table.
- The oxidation state of the substance is +5.
Key Terms: Protactinium, Uranium, Isotopes, Thorium, Oxide, Alpha Decay, Radioactive, Parts Per Million, Actinide, Plutonium, Periodic Table, Atomic Number, Oxidation State, Temperature
What is Protactinium?
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Protactinium, also known as protoactinium, is an organic compound that is positioned left of uranium and right of thorium in the periodic table. It is a silvery-grey, radioactive substance that is found in a few parts per trillion of Earth’s crust.
- Protactinium was first predicted by Dmitri Mendeleev in 1871.
- He predicted that an element exists between thorium and uranium.
- The metal was created by American chemist Aristid V. Grosse.
- It is made of 29 isotopes, all of which are radioactive in nature.
- Since protactinium is radioactive and toxic, there is no practical application of the element.
Protactinium
Preparation of Protactinium
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Protactinium was extracted using the uranium ores for scientific studies before nuclear reactors were invented. It is now produced mainly as an intermediate product of nuclear fission.
- It is produced in the thorium high-temperature reactors (the period given are half-lives).
23290Th +10n ------→ 23390Th ----→ 23391Pa --------→ 23392U
Thorium-230 can be converted to the beta-decaying thorium-231 by irradiating it with the slow neutrons, or thorium-232 can be irradiated with the fast neutrons to produce thorium-231 and 2 neutrons.
- Protactinium metal can be manufactured by reducing its fluoride with calcium, lithium, or barium.
- The process is carried at a temperatures range of 1300°C to 1400°C.
Occurrence of Protactinium
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Protactinium is a naturally occurring element that is extremely rare and expensive. It can be found in two isotopes, 231Pa and 234Pa, with the latter appearing in two different energy levels.
- Protactinium-231 makes up nearly all-natural protactinium.
- It is an alpha emitter created by the decay of the uranium-235.
- On the other hand, protactinium-234 emits beta radiation.
- It is created by the decay of the uranium-238.
- Almost all the uranium-238 (99.8%) initially decays to the 234mPa isomer.
Protactinium is found in uraninite with concentrations ranging from 0.3 to 3 parts 231Pa ppm. Whereas the average content is around 0.3 ppm, some ores from the Democratic Republic of the Congo have around three ppm.
- Protactinium is homogeneously distributed in most natural materials and water.
- It is found at very low concentrations in the order of one part per trillion, corresponding to 0.1 picocuries (pCi)/g radioactivity.
- The concentrations in the sandy soil particles are approximately 500 times higher than in water.
- Loam soils and clays, such as bentonite, have much higher ratios of 2,000 and above.
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Properties of Protactinium
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The properties of protactinium are as follows:
- Protactinium is one of the rarest and expensive element on the Earth.
- It tends to occur about three parts per trillion.
- The compound is obtained as by-product in the uranium processing.
- It become superconductive when the temperature drop below 1.4K.
- Protactinium is paramagnetic at room temperature.
General Properties of Protactinium are as follows:
| Category | Data |
|---|---|
| Symbol | Pa |
| Atomic Number | 91 |
| 231.0359 g.mol -1 | |
| Element Category | Actinide |
| Period, Block | 7, f |
| Colour | silvery metallic |
| Other Names | Protoattinio, Protaktinium |
Chemical Properties of Protactinium
The chemical properties of protactinium are as follows:
- Protactinium belongs to the group of actinides.
- The atomic number of the compound is 91 and it belongs to f-block elements.
- Protactinium has melting and boiling point of around 1572°C, 2861.6°F, 1845.15 K and 4000°C, 7232°F, 4273 K respectively.
- Its electronic configuration is [Rn] 5f2 6d1 7s2.
- The compound is solid at 20 degree Celsius.
| Category | Data |
|---|---|
| 91 | |
| 91 | |
| Neutrons | 122 |
| [Rn] 5f2 6d1 7s2 | |
| Atomic Radius | 163 pm |
| Covalent Radius | 243 pm |
| Van der Waals Radius | 200 pm |
| Oxidation States | 5,4,3,2,0 |
| Crystal Structure | tetragonal |
| 1st Ionization Energy | 568 kJ·mol-1 |
Physical Properties of Protactinium
The physical properties of protactinium are as follows:
- Protactinium is a kind of radioactive and shiny metal that degrades in presence of oxides.
- It is made of 5 isotopes with mass number between 212 to 238.
- The isotopes are formed by decaying of uranium through gamma radiation.
- It is denser than thorium but lighter than uranium.
- The metal crystallizes at room temperature and form tetragonal structure.
| Category | Data |
|---|---|
| Melting Point | 1572°C, 2861.6°F, 1845.15 K |
| Boiling Point | 4000°C, 7232°F, 4273 K |
| 15370 kg·m3 | |
| Density at 20°C | 15.4 g/cm3 |
| Superconductivity Temperature | 1.4 [or -271.7 °C (-457.1 °F)] K |
| Heat of Fusion (kJ·mol-1) | 16.7 |
| 47 W·m-1·K-1 | |
| (0 °C) 177 nΩ·m | |
| Key isotopes | 231Pa |
Compounds of Protactinium
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This section includes the list of binary protactinium compounds that contain halogens known as the halides, oxygen known as the oxides, hydrogen known as the hydrides, and other protactinium compounds.
- A formal oxidation number for the protactinium is supplied for each compound.
- However its utility is limited for the p-block elements in particular.
- An electrical configuration is also supplied based on that oxidation number.
The following are the most common oxidation numbers of protactinium in compounds.
Fluorides
The oxidation number of various compounds of fluorides are as follows:
- Protactinium tetrafluoride: PaF4
- Protactinium pentafluoride: PaF5
Chlorides
The oxidation number of various compounds of chlorides are as follows:
- Protactinium tetrachloride: PaCl4
- Protactinium pentachloride: PaCl5
Bromides
The oxidation number of various compounds of bromides are as follows:
- Protactinium tetrabromide: PaBr4
- Protactinium pentabromide: PaBr5
Iodides
The oxidation number of various compounds of iodides are as follows:
- Protactinium triiodide: Pal3
- Protactinium tetraiodide: Pal4
- Protactinium pentaiodide: Pal5
Isotopes of Protactinium
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Protactinium has thirty radioisotopes. The most stable of these is 231Pa, which has a half-lifespan of 32,760 years; 233Pa, which has a half-lifespan of 27 days; and 230Pa, which has a half-lifespan of 17.4 days.
- The half-live span of the remaining isotopes is less than 1.6 days.
- Majority of them have a half-life span of less than 1.8 seconds.
- Protactinium has two nuclear isomers, 217mPa, with a half-life span of 1.2 milliseconds.
- 234mPa with a half-life span of 1.17 minutes.
Alpha decay, which produces actinium isotopes, is the primary decay mode for the most stable isotope, 231Pa and lighter isotopes (211Pa to 231Pa).
- Beta decay produces uranium isotopes.
- It is the primary mode of decay for the heavier isotopes (232Pa to 240Pa).
Side Effects of Protactinium
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Various side effects of Protactinium on our health and environment are as follows:
Side Effect on Health
Protactinium is a highly radioactive and toxic metal. Researchers who work with it must exercise extraordinary caution in order to avoid being exposed to its radiation.
- Protactinium does not play any biological role.
- Although the gamma rays emitted by the protactinium-231 pose a tiny external risk.
- Protactinium is a health hazard if it is ingested into the body.
- Cancer caused by ionising radiation released by protactinium accumulate in the skeleton, liver, and kidneys.
- The lungs and gastrointestinal tract are also affected
Effect on Environment
Protactinium sticks to soil very strongly, and the concentration associated with the sandy soil particles is approximately 550 times greater than in interstitial water concentration ratios.
- For loam and clay soils it is significantly higher than around 2,000 and above.
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Things to Remember
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- Protactinium originated from the Greek word 'protos', which means first.
- It is used as prefix to the element actinium, which is generated by the radioactive decay of protactinium.
- There are no stable isotopes of protactinium.
- The greatest amount of protactinium ever discovered was 125 grams.
- It was recovered from 60 tonnes of nuclear waste by the United Kingdom Atomic Energy Authority.
- The metal can be used to date marine sediments when paired with the isotope thorium-230.
- One gram of protactinium is predicted to cost around $280.
- Protactinium is considered harmful when absorbed into the body.
Sample Questions
Ques. Explain the following: (A) Is there any application of the Protactinium?
(B) Where does the protactinium element occur in the periodic table? (2 marks)
Ans.(A) Due to its scarcity, high radioactivity and toxicity, there are currently no uses for protactinium outside of basic scientific research.
(B) In the Periodic table, the protactinium element occurs in between the Uranium element and the thorium element.
Ques. Explain the following: (A) What kind of radiation does protactinium emit
(B) What is the melting point of protactinium? (2 marks)
Ans.(A) Uranium (U) decays into thorium (Th) and alpha (α) radiation is emitted in the first stage of the protactinium generator.
(B) The melting point of Protactinium is 1572°C, 2861.6°F, 1845.15 K.
Ques. Protactinium or Pa (Z = 91) = [Rn]5f26d17s2. Why are we writing it as [Rn]? Why 5f2 and Not 5f14? (2 marks)
Ans. We are writing Protactinium as [Rn] because Rn is a noble metal and it is completely filled with the electrons so instead of writing the long electronic configuration, we can just write it as [Rn]. Rn has an atomic number 86 so after writing [Rn] we write atomic configuration after 86 here, after this there is only 5 electrons which is incompletely filled in the upcoming orbitals so we can't give 5f14.
Ques. Briefly explain the Protactinium element? (4 marks)
Ans. Protactinium metal is a closely packed, silvery-grey material with a bright metallic lustre that it retains in air for a short time, but it readily reacts with oxygen, water vapour, and inorganic acids to form various compounds.
- In solid compounds, protactinium will be more stable in the oxidation state +5, but it also appears to exist in the oxidation states +4, +3, and +2.
- In solution, the +5 state gets rapidly hydrolyses by grouping with hydroxide ions to form soluble or insoluble hydroxy-oxide solids that adhere to the surfaces of the vessels in which it is contained.
- A variety of protactinium compounds, some of which are coloured, are known.
- Below 1.4K, the element is superconductive.
Ques. Whether the protactinium acts more like an actinide or like a transition metal? (3 marks)
Ans. The outer electron shells of a protactinium atom hold the key to determining whether it behaves more like an actinide or a transition metal. Each shell is assigned a number (1-7) as well as a letter by scientists (s, p, d or f).
- The shell that an element's outer electrons occupy, in terms of the number and letter, describes its family.
- It influences a wide range of its chemical and physical behaviour.
Ques. Give the Precautions of Protactinium? (3 marks)
Ans. Because protactinium is found in lower concentrations in most of the natural materials and products, it is consumed with water or food and inhaled with air. Only about 0.05 % of ingested protactinium is absorbed into the blood, with the rest excreted. Approximately 40% of the protactinium in bone blood deposits is transported to the kidneys, 15% to the liver, and the remainder is excreted.
Ques. A sample of a protactinium-234 of mass 100g has a half-life of 6.7 hours.
(a) What fraction of the sample has not decayed after 20.1 hours?
(b) What is the mass of undecayed protactinium-234 after period of time? (3 marks)
Ans.The process is as follows:
(a) 20.1 hours = 20.16.7 half-life = 3 half-life
After 20.1 hours, the fraction that has not decayed = 18
(b) Mass of undecayed protactinium-234
= 18 x 100 = 12.5g
Ques. Write the electronic configuration of? (5 marks)
(i) Ce4+ (ii) Th4+ (iii) Cu+ (iv) Cr3+ (v) Mn2+ (vi) Lu2+ (vii) Co2+ (viii) Pm3+
Ans:
(i) Ce4+: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6
Or, [Xe]54
(ii) Th4+: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6
Or, [Rn]86
(iii) Cu+: 1s2 2s2 2p6 3s2 3p6 3d10
Or, [Ar]18 3d10
(iv) Cr3+: 1s2 2s2 2p6 3s2 3p6 3d3
Or, [Ar]18 3d3
(v) Mn2+: 1s2 2s2 2p6 3s2 3p6 3d5
Or, [Ar]18 3d5
(vi) Lu2+: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 4f14 5d1
Or, [Xe]54 4f14 5d1
(vii) Co2+: 1s2 2s2 2p6 3s2 3p6 3d7
Or, [Ar]18 3d7
(viii) Pm3+: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 4f4
Or, [Xe]54 4f4
Ques. Explain the isotopes of protonium? (2 marks)
Ans. Thirty radioisotopes of protonium have been identified; the three most stable are 231Pa, with a half-life of 32,760 years, 233Pa, with a half-life of 27 days, and 230Pa, with a half-life of 17.4 days. The remainder of the isotopes have half-lives of less than 1.6 days, with most of them lasting less than 1.8 seconds. There are two nuclear isomers of protonium: 217mPa, which has a half-life of 1.2 milliseconds, and 234mPa, which has a half-life of 1.17 minutes.
Ques. A sample of a protactinium-234 of mass 100g has a half-life of 6.7 hours.
(a) What fraction of the sample has not decayed after 21.1 hours?
(b) What is the mass of undecayed protactinium-234 after period of time? (3 marks)
Ans.The process is as follows:
(a) 21.1 hours = 21.16.7 half-life = 3 half-life
After 21.1 hours, the fraction that has not decayed = 18
(b) Mass of undecayed protactinium-234
= 18 x 100 = 12.5g
Ques. Explain the effects of protactinium on human health? (3 marks)
Ans. Protactinium is a hazardous and extremely radioactive metal. When working with it, researchers need to be extremely careful to prevent radiation exposure. Protactinium has no biological function.
- Protactinium is typically only harmful to health if it is swallowed into the body.
- However, there is a very small external risk from the gamma rays released by protactinium-231 and several short-lived decay products of actinium-227.
- The primary health danger is cancer brought on by ionizing radiation emitted by protactinium that has accumulated in the kidneys, liver, and skeleton.
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