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Structure of Atom — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistryStructure of Atom5 Marks
Question
  1. Write outer electronic configuration of Cr atom. Why are half filled orbitals more stable?
  2. An electron has a velocity of $50 \mathrm{~ms}^{-1}$, accurate upto $99.99 \%$. Calculate the uncertainty in locating its position. (Mass of electron $=9.1 \times 10^{-31} \mathrm{~kg}, \mathrm{~h}=6.6 \times 10^{-34} \mathrm{~J}$ s)
  3. Write the atomic number of the element in which filling of 3d sub-shell in the atom just starts.
✓

Answer

  1. Cr(24): $1 s^2 2 s^2 2 p^6 3 s^2 3 p^6 4 s^1 3 d^5$
Half filled orbitals are more stable because of symmetrical distribution of electrons and exchange energy is maximum.
  1. $\Delta\text{V}=50\times\big[(100-99.99)\%\big]$
$=50\times\frac{0.01}{100}=50\times10^{-4}$
$=5\times10^{-3}\text{ms}^{-1}$
$\Delta\text{x}.\Delta\text{V}=\frac{\text{h}}{4\pi\text{m}}$
$\Delta\text{x}\times5\times10^{-3}\text{ms}^{-1}=\frac{6.6\times10^{-34}\text{Js}}{4\times3.142\times9\times10^{-31}\text{kg}}$
$\Rightarrow\Delta\text{x}=\frac{6.6\times10^{-34}\text{Js}}{4\times3.142\times9.1\times10^{-31}\text{kg}\times5\times10^{-3}\text{ms}^{-1}}$
$=1.154\times10^{-2}\text{m}$
  1. Scandium (Atomic number 21) is the element in which filling of 3d orbitals starts.

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