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Explain the following: (i) Why argon (...

Explain the following:
(i) Why argon (atomic mass `= 39.94)` has been placed before potassium (atomic mass `= 39.10)` in the Modern periodic table?
(ii) There are only `14` anthanides and only `14` actinides in Modern peridoic table.

Text Solution

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The correct Answer is:
(i) In modern periodic table, elements have been placed in order of their increasing atomic numbers. The atomic number of argon is 18 and that of potassium is 19. Thus, argon has been placed before potassium
(ii) In lanthanides and actinides, the differentiating electron enters to `(n -2)` f-subshell. The maximum capacity of f-subshell is of 14 electrons. Thus, there are only 14 anthanides `(4f^(1-14))` and only 14 actinides `(5f^(1-14))`.
(i) In modern periodic table, elements have been placed in order of their increasing atomic numbers. The atomic number of argon is 18 and that of potassium is 19. Thus, argon has been placed before potassium
(ii) In lanthanides and actinides, the differentiating electron enters to `(n -2)` f-subshell. The maximum capacity of f-subshell is of 14 electrons. Thus, there are only 14 anthanides `(4f^(1-14))` and only 14 actinides `(5f^(1-14))`.
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State giving reason why argon(atomic mass =39.94) has been rightly placed before potassium (atomic mass=39.01) in the Modern Periodic Table.

State giving clear explanation why argon (atomic weight = 39.9) has been rightly placed before potassium (atomic weight 39.10 ) in the periodic table.

Knowledge Check

  • Assertion: Argon (at mass 39.94) has been placed before potassium (at mass 39.10) in the modern periodic table. Reason: In modern periodic table, elements have been placed in order of their increasing atomic numbers.

    A
    If both assertion and reason are true and reason is the correct explanation of assertion
    B
    If both assertion and reason are true but reason is not the correct explanation of assertion
    C
    If assertion is true but reason is false
    D
    If both assertion and reason are false

  • Which of the following statement(s) about Modem Periodic Table are incorrect ? (i) The elements in the Modern Periodic Table are arranged on the basis of their decreasing atomic number. (ii) The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic masses. (iii) Isotopes are placed in adjoining group(s) in the Periodic Table. (iv) The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic number.

    A
    (i) only.
    B
    (i), (ii) and (iii)
    C
    (i), (ii) and (iv)
    D
    (iv) only.

  • Which of the following statements (s) about the modern periodic table are incorrect ? (i) The elements in the modern periodic table are arranged on the basis of their decreasing atomic numbers (ii) The elements in the modern periodic table are arranged on the basiss of their increasing atomic mases. (iii) Isotopes are placed in adjoining group(s) in the periodic table (iv) The elements in the modern periodic table are arranged on the basis of their increasing atomic number.

    A
    Only (i)
    B
    (i),(ii) and (iii)
    C
    (i), (ii) and (iv)
    D
    Only (iv)

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