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Terbium is a chemical element represented with the symbol Tb. It was discovered by Carl Mosander in the year 1843. It has an atomic number of Terbium 65. It is an f-block element and placed in the sixth table. It is the ninth member of the lanthanides series. The electronic configuration of Terbium is given as [Xe] 4f9 6s2. Terbium is a soft, silver-white, ductile element found rarely in nature and can be cut easily with a knife. It is an electro-positive metal that reacts with water, evolving hydrogen gas.It is used as a doping agent in many chemicals, one of which is calcium fluoride.
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Key Terms: Periodic Table, Terbium, electronic configuration, atomic mass, period, lanthanide
Properties of Terbium
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Physical Appearance:
Silver-white in color, solid, soft, ductile, and malleable. Soft enough to be cut with a knife.
Occurrence:
Rarely found and never occurs in free form in nature. Occurs in a solid state at room temperature and pressure. Found in ores of monazite, bastnasite, and cerite.
Melting point: 1629 K.
Boiling point: 3396 K.
Density: 8.23 g/cm3
Oxidation States: It shows five oxidation states: 0, +1, +2, +3, +4.
Electronic Configuration: [Xe] 4fâ1 6s2
Heat of fusion: 10.15 kJ/mol.
Heat of vaporization: 391 KJ/mol.
Molar heat capacity: 28.91 J/mol.K.
Relative Atomic Mass: 158.925
Key Isotopes: 159Tb
Toxicity: Mildly toxic in nature
Read More: Number of Moles Formula
Chemical Reactions
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- Terbium is electropositive in nature. It gets oxidized when exposed to an acid.
2 Tb (s) + 3 H2SO4 → 2 Tb3+ + 3 SO2−4 + 3 H2↑
- Terbium gets oxidized in the presence of air and forms terbium oxide.
8Tb + 7O2 → 2Tb4O7
Applications of Terbium
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- Terbium is used in making alloys. The alloys of Terbium are used in the manufacturing of several electronic devices and products like sensors and actuators.
- Terbium is used as a doping agent in many chemical compounds like calcium fluoride, calcium tungstate, and strontium molybdate. These compounds are used in the production of solid-state devices.
- Terbium works as a crystal stabilizer of fuel cells.
- Terbium is also used in the production of color tv tubes and fluorescent lights.
- Terbium is also used in detecting endospores.
Read More: Rate Determining Step
Things to Remember
- The atomic symbol of terbium is Tb. It is an f-block element.
- Its atomic number is 65 and its atomic mass is 158.925.
- Terbium belongs to the lanthanides group and is placed in the 6th period.
- Terbium is electropositive in nature and reacts with water evolving hydrogen gas.
- Terbium gets oxidized when reacted with an acid. It is stable in air but gets oxidized slowly.
- India is one of the main mining areas of terbium.
- Terbium possesses ferromagnetic properties below 219K and antiferromagnetic properties above 219 K.
- Terbium is an element which never occurs in free form in nature.
Sample Questions
Ques. Which of the following is not an actinoid? (2 marks)
(i) Curium (Z = 96)
(ii) Californium (Z = 98)
(iii) Uranium (Z = 92)
(iv) Terbium (Z = 65)
Explanation: Terbium(Z = 65) is an f-block element and placed in the sixth table. It is the ninth member of the lanthanides series. The electronic configuration of Terbium is given as [Xe] 4fâ¹ 6s². Thus, it cannot be classified as an actinoid.
Ques. The elements in which electrons are progressively filled in 4f-orbital are called _______ (2 marks)
(i) actinoids
(ii) transition elements
(iii) lanthanoids
(iv) halogens
Answer: (iii) lanthanoids
Explanation: lanthanoids are a series of 15 consecutive chemical elements in the periodic table from lanthanum to lutetium with atomic numbers 58-71. When configured according to the rules, the electronic configuration of the elements in the lanthanoid series go upto filling the 4f-orbital.
Ques. In the Modern Periodic Table, the period indicates the value of ______ (2 marks)
(i) Atomic Number
(ii) Azimuthal Quantum Number
(iii) Atomic Mass
(iv) Principal Quantum Number
Answer: (iv) Principal Quantum Number
Explanation: The value of the principal quantum number(n) for the outermost shell or the valence shell indicates the period in the Modern periodic Table.
Ques. Write a short note on Terbium. (3 marks)
Answer: Terbium is a chemical element represented with the symbol Tb. It has an atomic number of 65. It is an f-block element and placed in the sixed table. It is the ninth member of the lanthanides series. The electronic configuration of Terbium is given as [Xe] 4fâ¹ 6s²
Terbium is a soft, silver-white element ductile element found rarely in nature and can be cut easily with a knife. It is an electro-positive metal that reacts with water, evolving hydrogen gas. It has a melting point of 1629 K and a boiling point of 3396 K. Its density is 8.23 g/cm3.
Terbium is used as a doping agent with many chemicals. It is also used in making alloys and electrical devices. It doesn’t have any biological use. But, it can be harmful and cause irritation when it comes in contact with eyes and skin.
Ques. Give the applications of Terbium. (3 marks)
Answer: Applications of Terbium are as follows:
- Terbium is used in making alloys. The alloys of Terbium are used in the manufacturing of several electronic devices and products like sensors and actuators.
- Terbium is used as a doping agent in many chemical compounds like calcium fluoride, calcium tungstate, and strontium molybdate. These compounds are used in the production of solid-state devices.
- Terbium works as a crystal stabilizer of fuel cells.
- Terbium is also used in the production of color tv tubes and fluorescent lights.
- Terbium is also used in detecting endospores.
Ques. Give the properties of Terbium. (3 marks)
Answer: Terbium is a chemical element represented with the symbol Tb. It has an atomic number of Terbium 65. Some of the Properties of Terbium are as follows:
- Terbium is silver-white in colour, soft, ductile, and malleable.
- It has a melting point of 1629 K and a boiling point of 3396 K.
- The density of terbium is 8.23 g/cm3
- Terbium occurs at a solid state at room temperature and pressure.
Ques. Explain that Nitrogen has positive electron gain enthalpy whereas oxygen has negative. However, oxygen has lower ionisation enthalpy than nitrogen. (3 marks)
Answer:
The outermost electronic configuration of nitrogen (2s2 2px 1 2py 1 2pz 1) is very stable because the p-orbital is half filled.
Addition of extra electrons to any of the 2p orbital requires energy.
Oxygen has 4 electrons in 2p orbitals and acquires stable configuration i.e., 2p3 configuration after removing one electron.
Thus, Nitrogen has positive electron gain enthalpy whereas oxygen has negative. However, oxygen has lower ionisation enthalpy than nitrogen.
Ques. What is the basic difference in approach between Mendeleev's Periodic Law and the Modern Periodic Law? (2 marks)
Answer:
Mendeleev's Periodic Law states that the physical and chemical properties of elements are periodic functions of their atomic weights.
On the other hand, the Modern Periodic Law states that the physical and chemical properties of elements are periodic functions of their atomic numbers.
Ques. On the basis of quantum numbers, justify that the sixth period of the periodic table should have 32 elements. (5 marks)
Answer:
In the periodic table, a period indicates the value of the principal quantum number (n) for the outermost shells. Each period begins with a principal quantum number
The value of n for the sixth period is 6. For n = 6, azimuthal quantum number (l) can have values of 0, 1, 2, 3, 4.
According to Aufbau's principle, electrons are added to different orbitals in order of their increasing energies. The energy of the 6d subshell is even higher than that of the 7s subshell.
In the 6th period, electrons can be filled in only 6s, 4f, 5d, and 6p subshells. Now, 6s has one orbital, 4f has seven orbitals, 5d has five orbitals, and 6p has three orbitals, therefore, there are a total of sixteen (1 + 7 + 5 + 3 = 15) orbitals available.
According to Pauli's exclusion principle, each orbital can accommodate a maximum of 2 electrons. Thus, 16 orbitals can accommodate a maximum of 32 electrons. Hence, the sixth period of the periodic table should have 32 elements.
Ques. i)Where would you locate the element with Z =114 in terms of period and group? (3 marks)
ii) give any 4 characteristic properties of p-block elements. (2 marks)
ii) Characteristics properties of p-block
Answer: Elements With atomic numbers from Z = 87 to Z = 114 are present in the 7th period of the periodic table. Thus, the element with Z = 114 is present in the 7th period of the periodic table.
In the 7th period, first two elements with Z = 87 and Z = 88 are s-block elements, the next 14 elements excluding Z = 89 i.e., those with Z = 90 - 103 are f - block elements, ten elements Kith Z = 89 and Z = 104 - 112 are d block elements, and the elements Z = 113 -118 are p — block elements.
Therefore, the element with Z = 114 is the second p — block element in the 7th period. Thus, the element with Z = 114 is present in the 7th period and 4th group of the periodic table.
(ii) Characteristic properties of p-block are as follows:
- p-block elements consist of both metals and non-metals.
- p-block elements form covalent bonds with other elements.
- The ionisation enthalpies of p-block elements are relatively higher than s-block elements.
- Some of the p-block elements show variables or more than one oxidation state.
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