Q2: Among the following, the correct statement(s) for electrons in an atom is(are) [JEE Advanced 2024 Paper 1]
(a) Uncertainty principle rules out the existence of definite paths for electrons.
(b) The energy of an electron in 2s orbital of an atom is lower than the energy of an electron that is infinitely far away from the nucleus.
(c) According to Bohr's model, the most negative energy value for an electron is given by n = 1, which corresponds to the most stable orbit.
(d) According to Bohr's model, the magnitude of velocity of electrons increases with increase in values of n.
Ans: (a), (b), (c)
Let's analyze each statement one by one:
Option A: Uncertainty principle rules out the existence of definite paths for electrons.
This statement is correct. The Heisenberg Uncertainty Principle states that it is impossible to simultaneously know both the exact momentum and the exact position of a particle. Therefore, the concept of a definite path for electrons is not applicable according to quantum mechanics.
Option B: The energy of an electron in 2s orbital of an atom is lower than the energy of an electron that is infinitely far away from the nucleus.
This statement is also correct. The energy of an electron in any bound state (such as the 2s orbital) is always lower (more negative) than that of an electron at an infinite distance from the nucleus (which would have zero energy). This is because an electron infinitely far away from the nucleus is considered to be free from nuclear attraction and thus its potential energy is zero.
Option C: According to Bohr's model, the most negative energy value for an electron is given by n = 1, which corresponds to the most stable orbit.
This statement is correct as well. In Bohr’s model of the atom, the energy levels of electrons are given by:
En = -13.6 eVn²
The energy is most negative when n = 1, indicating the most stable orbit and thus the lowest energy state (the ground state).
Option D: According to Bohr's model, the magnitude of velocity of electrons increases with increase in values of n.
This statement is incorrect. According to Bohr’s model, the speed of an electron in a circular orbit around the nucleus decreases with an increase in the principal quantum number n. The velocity vn is given by the formula:
vn = 2.18 × 10⁶ m/sn
where n is the principal quantum number. Hence, as n increases, vn decreases.
Therefore, the correct statements are:
Option A, Option B, and Option C.
where r is in pm, n is the principal quantum number, and Z is the atomic number.
2. For a He+ ion, Z = 2.
3. We are given the initial radius r2=105.8 pm and the final radius r1=26.45 pm.
4. We can substitute these radii into the equation for r to find the corresponding quantum numbers.
For r2 = 105.8 pm, we get :
which gives n2 = 2.
Similarly, for r1 = 26.45 pm, we get :
which gives n1 = 1.
5. Therefore, the transition is from n2 = 2 to n1 = 1.
6. The energy difference during this transition is equal to the energy of the emitted photon, which is given by :
where ℎ is the Planck's constant, c is the speed of light, RH is the Rydberg constant, and λ is the wavelength of the photon.
7. Substituting all known values into this equation gives :
Solving this equation yields λ = 30 × 10−9 m, or 30 nm.
8. So, the wavelength of the emitted photon during the transition is 30 nm.
Option (A) is correct.
Option (B) is incorrect.
π∗ orbital has zero node is the plane which is perpendicular to the molecular axis and goes through the center of molecule.
So, option (C) is incorrect.
π∗ Orbital has one node in the xy− plane containing the molecular axis.
Option (D) is correct.
=
Velocity, = V cm/s.
Using de-Broglie equation,
= 30 cm/s
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JEE Advanced Previous Year Questions (2018 - 2024): Structure of Atom
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Ans: − 5242.41
Given that, electrons and nucleus are at infinite distance, so potential energy of H-atom is taken as zero.
Therefore, according to Bohr's model, potential energy of a H-atom with electron in its ground state
= −27.2 eV
At d = d0, nucleus-nucleus and electron-electron repulsion is absent.
Hence, potential energy will be calculated for 2 H atoms = −2 × 27.2 eV = −54.4 eV
Potential energy of 1 mol H atoms in kJ
=
= − 5242.4192 KJ
Which of the following options has the correct combination considering List-I and List-II?
(a) (III), (P)
(b) (III), (S)
(c) (IV), (U)
(d) (IV), (Q) [JEE Advanced 2019 Paper 2]
Ans: (a)
(III) Kinetic energy of the electron in nth orbit,
From List-II, correct match is (III, P)
(IV) Potential energy of the electron in the nth orbit,
From List-II, correct match is (IV, P).
Hence, correct matching from List-I and List-II on the basis of given options is (III, P).
Q2: Consider the Bohr's model of a one-electron atom where the electron moves around the nucleus. In the following List-I contains some quantities for the nth orbit of the atom and List-II contains options showing how they depend on n.
Which of the following options has the correct combination considering List-I and List-II?
(a) (II), (R)
(b) (I), (P)
(c) (I), (T)
(d) (II), (Q) [JEE Advanced 2019 Paper 2]
Ans: (c)
(I) Radius of the nth orbit, r = 0.529 x n2 / Z
Here, r ∝ n2
From List-II, correct match is (I, T)
(II) Angular momentum of the electron,
From List - II, correct match (II, S)
Hence, correct matching from List-I and List-II on the basis of given options is (I, T).
Q3: The ground state energy of hydrogen atom is −13.6 eV. Consider an electronic state ψ of He+ whose energy, azimuthal quantum number and magnetic quantum number are −3.4 eV, 2 and 0, respectively.
Which of the following statement(s) is(are) true for the state ψ?
(a) It is a 4d state
(b) The nuclear charge experienced by the electron in this state is less than 2e, where e is the magnitude of the electronic charge
(c) It has 2 angular nodes
(d) It has 3 radial nodes [JEE Advanced 2019 Paper 2]
Ans: (a) & (c)
Given, ground state energy of hydrogen atom = −13.6 eV
Energy of He+ = −3.4 eV, Z = 2
Energy of He+,
Given, azimuthal quantum number (l) = 2 (d − subshell)
Magnetic quantum number (m) = 0
∴ Angular nodes (l) = 2
Radial node = n − l − 1 = 4 − 2 − 1 = 1
nl = 4d state
Hence, options (a), (c) are correct.
Q4: Which of the following statement(s) is(are) correct regarding the root mean square speed (Urms) and average translational kinetic energy (Eav) of a molecule in a gas at equilibrium?
(a) Urms is inversely proportional to the square root of its molecular mass.
(b) Urms is doubled when its temperature is increased four times.
(c) Eavg is doubled when its temperature is increased four times.
(d) Eavg at a given temperature does not depend on its molecular mass. [JEE Advanced 2019 Paper 1]
Ans: (a), (b) & (d)
The explanation of given statements are as follows :
(a) Urms is inversely proportional to the square root of its molecular mass.
Hence, option (a) is correct.
(b) When temperature is increased four times then Urms become doubled.
Hence, option (b) is correct.
(c) and (d) Eav is directly proportional to temperature but does not depends on its molecular mass at a given temperature as . If temperature raised four times than Eav becomes four time multiple.
Thus, option (c) is incorrect and option (d) is correct.
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