CBSE Class 11 Chemistry Atomic Structure Flash Cards

Question. If the atom ₁₀₀Fm²⁵⁷ follows the Bohr model and the radius of ₁₀₀Fm²⁵⁷ is n times the Bohr radius, then find n:
a. 100
b. 200
c. 4
d. 1/4
Answer : D

Question. An energy of 24.6 eV is required to remove one of the electrons from a neutral helium atom. The energy (in eV) required to remove both the electrons from a neutral helium atom is:
a. 79.0
b. 51.8
c. 49.2
d. 38.2
Answer : A

Question. Which one of the following is/are true for the cathode rays?
a. they have kinetic energy
b. they cause certain substances to fluoresce
c. they travel in straight line
d. they are electromagnetic waves
Answer : A, B, C

Question. The specific charge of the cathode rays is:
a. a universal constant
b. independent of the place of earth
c. independent of the nature of gas in discharge tube
d. independent of the material of discharge tube
Answer : ALL

Question. In Thomson’s experiment, if the velocity of electron is greater than E/B, then:
a. the electron will not reach the underflected spot
b. the electron will move to a spot below the underflected spot
c. the electron will move to a spot above the underflected spot
d. the electron will move to the underflected spot
Answer : A, B

Question. Which of the following statements are true for the cathode rays?
a. They travel along straight line
b. They emit X-rays when strike a metal
c. They are electromagnetic waves
d. They are not deflected by magnetic field
Answer : A, B

Question. The potential difference applied to an X-ray tube is increased. As a result, in the emitted radiation:
a. the intensity increases
b. the minimum wave length increases
c. the intensity remains unchanged
d. the minimum wave length decreases
Answer : C, D

Question. The shortest wave length produced in an X-ray tube operated at 0.5 million volt is:
a. dependent on the target material
b. 0.025 Å approximately
c. half of the shortest wave length produced which the tube operating at 1 million volts
d. dependent only on the target material and not on the operating voltage
Answer : B, C

Question. When α– particle are sent through a thin metal foil, most of them go straight through the foil because:
a. α– particles are much heavier than electrons
b. α– particles are positively charged
c. most part of the atom is empty space
d. α– particles move with high velocity
Answer : A, C

Question. Which of the following statements about X-rays is/are an accepted fact(s)?
a. They are generated when fast moving electrons strike a metal target
b. They can penetrate through a thin sheet of Al.
c. When they traverse a space across which there is a magnetic field and electric field perpendicular to one another, they are undeviated 
d. When they traverse a space across which there is a magnetic field and electric field parallel to one another they describe a circular path
Answer : A, B, C

Question. Which of the following statement (s) is / are correct?
a. An atom with a vacancy has smaller energy than a neutral atom
b. K X-ray is emitted when a hole makes a jump from the K shell to some other shell
c. The wavelength of K X-ray is smaller than the wavelength of L X-ray of the same material
d. The wavelength of K_α X-ray is smaller than the wavelength of K_β X-ray of the same material
Answer : B, C

Question. An X-ray is operating at 50 kV and 20 mA. The target material of the tube has a mass of 1.0 kg and specific heat 495J kg–1ºC–1. One percent of the supplied electric power is converted into X-ray and entire remaining energy goes into heating the target. Then,
a. the average rate of rise of temperature of the target would be 2ºC/s
b. the minimum wavelength of the X-rays emitted is about 0.25×10^–18m
c. a suitable target material must have a high melting temperature
d. a suitable target material must have low thermal conductivity
Answer : A, B

Question. When an electron strikes the target in a Coolidge tube, its entire kinetic energy:
a. is converted into a photon
b. may be converted into a photon
c. is converted into heat
d. may be converted into heat
Answer : B, D

Question. For harder X-rays:
a. the wavelength is higher
b. the intensity is higher
c. the frequency is higher
d. the photon energy is higher
Answer : C, D

Question. In Bohr model of hydrogen atom:
a. the radius of nth orbit is proportional to n²
b. the total energy of electron in n^th orbit is proportional to n
c. the angular momentum of the electron in an orbit is an integral multiple of h/2π
d. the magnitude of the potential energy of an electron in any orbit is greater than its kinetic energy
Answer : A, B, C

Question. For which of the following sets of four quantum numbers, an electron will have the highest energy?
    n      l      m         s
a. 3      2      1      +1/2
b. 4      2      1      +1/2
c. 4      1      0      –1/2
d. 5      0      0      –1/2
Answer : B

Question. What is the maximum number of electrons which can be accommodated in an atom in which the highest principal quantum number value is 4?
a. 10
b. 18
c. 32
d. 54
Answer : C

Question. The four quantum numbers of the valence electron of potassium are:
a. 4, 1, 0 and 1/2
b. 4, 0, 1 and 1/2
c. 4, 0, 0 and + 1/2
d. 4, 1, 1 and 1/2
Answer : C

Question. Orbital angular momentum for a d-electron is:
a. 6h/2π
b. √6h/2π
c. 12h/2π
d. √12h/2π
Answer : B

Question. The maximum number of electrons present in an orbit l = 3 , is:
a. 6
b. 8
c. 10
d. 14
Answer : D

Question. When photons of energy 4.25 eV strike the surface of a metal A, the ejected photo electrons have maximum kinetic energy T_A (expressed in eV) and de Broglie wavelength λ_A .The maximum kinetic energy of the photo electrons liberated from another metal ‘B’ by photons of energy 4.20 eV is T_B =T_A – 1.5 (expressed in eV). If the de Broglie wavelength of these photo electrons is λ_B = 2λ_A , then
a. work function of A is 2.25 eV
b. work function of B is 4.20 eV
c. A T = 2 eV
d. B T = 2.50 eV
Answer : A, C

Question. Which of the following pairs have identical values of magnetic moment?
a. Zn²⁺ , Cu⁺
b. Co²⁺ , Ni²⁺
c. Mn²⁺ , Co²⁺
d. Mg⁴⁺ , Sc⁺
Answer : A, C

Question. If there were three possible values ( - 1/2, 0, + 1/2) for the spin magnetic quantum number s (m ), which of the following statement (s) is/are correct regarding a hypothetical Periodic
Table based on this conditions?
a. The first period would have only 2 vertical columns
b. The second period would have 12 elements
c. The Periodic Table would contain 27 group
d. The third period would have 12 elements
Answer : A, C, D

Question. Choose the correct statement among the following
a. Radial distribution function 2 2 (ψ 4π r ) gives the probability at a particular distance along one chosen direction:
b. ‘xz’ plane acts as a nodal plane for x 3p orbital
c. For ‘s’ orbital’s wave function is independent of θ and φ
d. ‘2p’ orbital with quantum number n = 2, l =1, m = 0, also shows the angular dependence.
Answer : C, D

Question. Choose the correct statement(s) regarding the photoelectric effect:
a. No electrons are ejected, regardless of the intensity of the radiation, unless the frequency equals or exceeds a threshold value characteristic of the metal
b. The kinetic energy of the ejected electrons varies linearly with the frequency of the incident radiation and its intensity
c. Even at low intensities, electrons are ejected immediately if the frequency is above the threshold value
d. An intense and a weak beam of monochromatic radiations differ in having number of photons and not in the energy of photons
Answer : A, C, D

Question. Mark out the correct statement (s) 
a. Electrons within a subshell for which l > 0 mean that the relatively greater electrostatics repulsion between two electrons in the same orbital within a sub shell as compared with occupancy of two orbitals having different m₁ values
b. Electrons in singly occupied orbitals tend to have their spins in the same direction so as to maximize the net magnetic moment
c. In the ground state, an atom adopts a configuration with the greatest number of unpaired electrons
d. Electrons in different orbitals with parallel spins show mutual attraction, so the electron-nucleus interaction is improved
Answer : A, B, C

Question. Which one of the following is/are true for the cathode rays?
a. they have kinetic energy
b. they cause certain substances to fluoresce
c. they travel in straight line
d. they are electromagnetic waves
Answer : A, B, C

Question. The specific charge of the cathode rays is:
a. a universal constant
b. independent of the place of earth
c. independent of the nature of gas in discharge tube
d. independent of the material of discharge tube
Answer : ALL 

Question. The potential difference applied to an X-ray tube is increased.
As a result, in the emitted radiation:
a. the intensity increases
b. the minimum wave length increases
c. the intensity remains unchanged
d. the minimum wave length decreases
Answer : C, D

Question. In Bohr model of hydrogen atom:
a. the radius of nth orbit is proportional to n²
b. the total energy of electron in nth orbit is proportional to n
c. the angular momentum of the electron in an orbit is an integral multiple of h / 2π
d. the magnitude of the potential energy of an electron in any orbit is greater than its kinetic energy
Answer : A, C, D

Question. Which of the following are in the ascending order of wavelength?
a. H_α ,H_β ,H_γ ... lines in Balmer series of hydrogen atom
b. Lyman limit, Balmer limit, Paschen limit in the hydrogen spectrum
c. Violet, blue, yellow, red colours in solar spectrum
d. None of these
Answer : B, C

Question. Continuous spectrum is produced by:
a. Incandescent electric bulb
b. sun
c. Hydrogen molecules
d. Na-vapour lamp
Answer : A, B

Question. A gas of monoatomic hydrogen is bombarded with a stream of electrons that have been accelerated from rest through a potential difference of 12.75 volt. In emission spectrum one can observe lines of:
a. Lyman series
b. Balmer series
c. Paschen series
d. Pfund series
Answer : A, B, C

Question. If the potential energy of the electron in the first allowed orbit in hydrogen atom is E, its:
a. Ionisation potential is –E/2
b. Kinetic energy is –E/2
c. Total energy is E/2
d. None of these true
Answer : A, B, C

Question. According to Bohr’s theory of the hydrogen atom, for the electron in the nth allowed orbit, the:
a. Linear momentum is proportional to (1/n)
b. the radius is proportional to n
c. The kinetic energy is proportional to (1/n²)
d. The angular momentum is proportional to n
Answer : A, C, D

Question. In an atom, the two electrons move round the nucleus in circular orbits of radii R and 4R. The ratio of the time taken by them to complete one revolution is:
a. 1/4
b. 4/1
c. 8/1
d. 1/8
Answer : D

Question. An energy of 24.6 eV is required to remove one of the electrons from a neutral helium atom. The energy (in eV) required to remove both the electrons from a neutral helium atom is:
a. 79.0
b. 51.8
c. 49.2
d. 38.2
Answer : A

Assertion and Reason

Note: Read the Assertion (A) and Reason (R) carefully to mark the correct option out of the options given below:
a. If both assertion and reason are true and the reason is the correct explanation of the assertion.
b. If both assertion and reason are true but reason is not the correct explanation of the assertion.
c. If assertion is true but reason is false.
d. If the assertion and reason both are false.
e. If assertion is false but reason is true.

Question. Assertion: The cation energy of an electron is largely determined by its principal quantum number.
Reason: The principal quantum number n is a measure of the most probable distance of finding the electron around the nucleus.
Answer : A

Question. Assertion: Nuclide ³⁰Al₁₃ is less stable than ⁴⁰Ca₂₀  Reason: Nuclides having odd number of protons and neutrons are generally unstable
Answer : A

Question. Assertion: The atoms of different elements having same mass number but different atomic number are known as isobars
Reason: The sum of protons and neutrons, in the isobars is always different
Answer : C

Class 11 Chemistry: Atomic Structure Flash Cards

Atomic Structure – Card 1

Two drawbacks of the Rutherford model are ______ and ______.

Answer: (i) It could not explain the stability of the atom: according to classical mechanics, an electron revolving around the nucleus is accelerated, so it should radiate energy and spiral into the nucleus. (ii) It could not explain the line spectrum of the hydrogen atom.

Two drawbacks of the Bohr model are ______ and ______.

Answer: (i) It could not explain the finer splitting of lines in the hydrogen spectrum (and the splitting in electric and magnetic fields, the Stark and Zeeman effects), and it failed for multi-electron atoms. (ii) It ignores the Heisenberg uncertainty principle: if we cannot locate an electron and tell its momentum at the same time, speaking of a definite trajectory (orbit) is meaningless. It also did not explain the dual nature of matter.

Give an example of (i) isotones, (ii) isotopes, (iii) isobars, (iv) isoelectronic species.

(i) Isotones: \(^{40}\text{Ca}\) and \(^{39}\text{K}\) (both have 20 neutrons).
(ii) Isotopes: \(^{35}\text{Cl}\) and \(^{37}\text{Cl}\).
(iii) Isobars: \(^{40}\text{Ca}\) and \(^{40}\text{K}\) (or \(^{40}\text{Ar}\)).
(iv) Isoelectronic species: Cl\(^-\) and Ar (18 electrons each).

How many electrons are present in (i) Ca\(^{2+}\), (ii) Fe\(^{3+}\), (iii) N\(^{3-}\)?

(i) 18 (20 − 2)
(ii) 23 (26 − 3)
(iii) 10 (7 + 3)

Arrange the electromagnetic radiations in terms of increasing energy.

Answer: Radio waves < microwaves < infrared < visible < ultraviolet < X-rays < gamma rays (energy increases with frequency).

Who discovered radioactivity?

Answer: Henri Becquerel (1896).

The isotopes of an element have the ______ (same, different) place in the periodic table.

Answer: same (they have the same atomic number).

What is the value of the angular momentum of an electron in the 5th orbit according to Bohr's theory?

Answer: \[ mvr=\frac{nh}{2\pi}=\frac{5h}{2\pi}\approx 5.27\times10^{-34}\ \text{J s} \]

Name three isotopes of hydrogen.

Answer: Protium (\(^1\)H), deuterium (\(^2\)H or D) and tritium (\(^3\)H or T).

Name the atom which does not contain even a single neutron.

Answer: Protium, \(^1_1\text{H}\) (ordinary hydrogen).

Card 2

What is the lowest energy state of an atom called?

Answer: The ground state.

In which series does the spectral line fall when an electron in a hydrogen atom jumps from the fourth energy level to the first energy level?

Answer: The Lyman series (transitions ending in n = 1; ultraviolet region).

Which is/are deflected towards the negative plate? (electron, proton, X-ray, alpha particles)

Answer: Protons and alpha particles (they carry positive charge). Electrons go to the positive plate and X-rays are not deflected.

Whose e/m value remains the same and independent of the nature of the gas and electrode taken in the discharge tube? (electron, proton)

Answer: The electron.

Two nuclides X and Y are isotonic with each other, with mass numbers 70 and 72 respectively. If the atomic number of X is 34, what is the atomic number of Y?

Answer: Neutrons in X = 70 − 34 = 36. Y has the same 36 neutrons, so its atomic number = 72 − 36 = 36.

Who proposed the plum-pudding model?

Answer: J. J. Thomson. (The source key says Rutherford, which is wrong; Rutherford proposed the nuclear model.)

The relationship between wavelength and frequency of an electromagnetic radiation is:

Answer: \( c=\nu\lambda \), i.e. \( \lambda=\dfrac{c}{\nu} \).

Write the expression of the de Broglie wavelength.

Answer: \( \lambda=\dfrac{h}{mv}=\dfrac{h}{p} \)

Write the mathematical expression of Heisenberg's uncertainty principle.

Answer: \( \Delta x\cdot\Delta p\ge\dfrac{h}{4\pi} \), i.e. \( m\,\Delta v\,\Delta x\ge\dfrac{h}{4\pi} \)

Name the three fundamental particles of an atom.

Answer: Electron, proton and neutron.

Card 3

Which has the higher de Broglie wavelength: an electron or a hydrogen atom?

Answer: The electron, because \( \lambda\propto 1/m \) and the electron is much lighter.

Which has the higher wavelength: red light or blue light?

Answer: Red light (about 700 nm, compared with about 450 nm for blue).

Which has the higher work function: Cs, Na or Li?

Answer: Li. The work function decreases down the group (Li > Na > Cs).

Isobars have the same number of (protons, electrons, nucleons, neutrons).

Answer: nucleons (the same mass number).

Write four properties of cathode rays.

Answer:

1. They travel in straight lines from the cathode to the anode, and cast shadows of objects in their path.
2. They are deflected by electric and magnetic fields towards the positive plate, showing that they are negatively charged.
3. They can rotate a small paddle wheel placed in their path, showing that they have mass (they are particles).
4. They produce fluorescence on a zinc sulphide screen and produce X-rays when they strike a metal target. Their e/m ratio is the same whatever the gas or the cathode used.

How many electrons and neutrons are present in tritium?

Answer: Tritium is \(^3_1\text{H}\): 1 electron and 2 neutrons.

Sunlight is ______ (monochromatic or polychromatic).

Answer: polychromatic (it contains many wavelengths).

Whose work function is the least in the following elements: K, Na, Cs, Li, Ag?

Answer: Cs (caesium).

______ series of lines of the hydrogen spectrum appears in the visible region.

Answer: The Balmer series (transitions ending in n = 2).

An electron can move only in those orbits for which its angular momentum is ______.

Answer: an integral multiple of \( h/2\pi \), i.e. \( mvr=nh/2\pi \).

Which of the following are isoelectronic species: Na\(^+\), K\(^+\), Mg\(^{2+}\), Ca\(^{2+}\), S\(^{2-}\), Ar?

Answer: Na\(^+\) and Mg\(^{2+}\) (10 electrons each); K\(^+\), Ca\(^{2+}\), S\(^{2-}\) and Ar (18 electrons each).

Card 4

The ionization energy of the hydrogen atom is ______ eV/atom.

Answer: 13.6 eV/atom (\(2.18\times10^{-18}\) J).

The Einstein equation for the photoelectric effect is ______.

Answer: \( h\nu=h\nu_0+\tfrac12 mv^2 \), i.e. \( \text{K.E.}=h\nu-h\nu_0 \).

The value of the Rydberg constant (R\(_H\)) is ______ J.

Answer: \( 2.18\times10^{-18} \) J (equivalently \(1.097\times10^{7}\ \text{m}^{-1}\)).

A phosphorescent material is ______.

Answer: ZnS (zinc sulphide).

The value of the Planck constant is h = ______ J s.

Answer: \( 6.626\times10^{-34} \) J s.

In \(^{235}_{92}\)U, the number of neutrons and nucleons present respectively are ______ and ______.

Answer: 143 neutrons (235 − 92) and 235 nucleons.

The charge on 1 mole of electrons is ______ coulombs.

Answer: \( 6.022\times10^{23}\times1.602\times10^{-19}\approx 96500 \) C (96485 C). The source key says 96350, which is slightly off.

The mass of one electron is ______ kg.

Answer: \( 9.109\times10^{-31} \) kg.

1 eV = ______ kJ/mol.

Answer: 96.485 kJ/mol (about 96.5).

The mass of (i) 1 mole of electrons is ______; (ii) 1 mole of neutrons is ______.

(i) \( 9.109\times10^{-31}\times6.022\times10^{23}=5.48\times10^{-7} \) kg.
(ii) \( 1.675\times10^{-27}\times6.022\times10^{23}=1.008\times10^{-3} \) kg (about 1.008 g). The source key gave \(3.97\times10^{-2}\) kg, which is wrong.

Name the two scientists who developed quantum mechanics independently in 1926.

Answer: Werner Heisenberg and Erwin Schrödinger (Heisenberg's matrix mechanics and Schrödinger's wave mechanics).

Differentiate between (i) monochromatic and polychromatic light, (ii) emission and absorption spectra.

(i) Monochromatic light has a single wavelength (one colour), e.g. a laser or sodium vapour lamp; polychromatic light contains many wavelengths (colours), e.g. sunlight.

(ii) An emission spectrum is obtained when an excited atom gives out radiation as electrons fall to lower levels: bright lines on a dark background. An absorption spectrum is obtained when white light is passed through a substance which absorbs certain wavelengths: dark lines on a bright continuous background (at the same positions).

Card 5

What is the shape of a p-orbital?

Answer: Dumb-bell shaped.

An atom of an element has its K and L shells completely filled with electrons. The atomic number of the element is ______.

Answer: 10 (2 + 8 electrons; the element is neon).

The maximum number of electrons present in the M shell is ______.

Answer: 18 (\(2n^2\) with n = 3).

The maximum number of electrons present in an f sub-shell is ______.

Answer: 14 (7 orbitals × 2).

______ number of radial nodes are present in a 4s orbital.

Answer: 3 (radial nodes = n − l − 1 = 4 − 0 − 1).

Orbitals having the same energy are called ______ orbitals.

Answer: degenerate

The number of sub-shells associated with n = 4 is ______.

Answer: 4 (s, p, d and f).

How many electrons will be present in the sub-shells having m\(_s\) value of −1/2 for n = 4?

Answer: 16 (the shell holds 32 electrons, half of which have spin −1/2).

How many electrons in an atom may have the following quantum numbers? (a) n = 4, m\(_s\) = +1/2; (b) n = 3, l = 0.

(a) 16
(b) 2 (the 3s orbital holds two electrons)

Which quantum number specifies the shape of an orbital in an atom?

Answer: The azimuthal (angular momentum) quantum number, l.

Card 6

The electronic configuration of a certain atom is 1s\(^2\)2s\(^2\)2p\(^6\)3s\(^2\)3p\(^6\)4s\(^1\). Find the atomic number of the atom.

Answer: 2 + 2 + 6 + 2 + 6 + 1 = 19 (potassium).

The ground state configuration of Cu is ______ and of Cl is ______.

Answer: Cu: [Ar] 3d\(^{10}\) 4s\(^1\) (extra stability of the completely filled d sub-shell). Cl: [Ne] 3s\(^2\) 3p\(^5\).

An element has 2 K, 8 L and 9 M electrons. Find out (i) the atomic number, (ii) the number of p-electrons, (iii) the number of protons, (iv) the total number of d-electrons, (v) the number of electrons occupying spherically symmetric orbitals, (vi) the number of electrons whose azimuthal quantum number is one.

Total electrons = 2 + 8 + 9 = 19, so the element is potassium (taking the ground-state configuration 1s\(^2\)2s\(^2\)2p\(^6\)3s\(^2\)3p\(^6\)4s\(^1\)).

(i) 19
(ii) 12 (2p\(^6\) and 3p\(^6\))
(iii) 19
(iv) 0 (the 19th electron goes to 4s, not 3d)
(v) 7 (the s electrons: 2 + 2 + 2 + 1)
(vi) 12 (the p electrons, l = 1)

______ number of angular nodes are present in a 4f orbital.

Answer: 3 (angular nodes = l = 3).

Differentiate between an orbit and an orbital.

An orbit is a definite circular path of an electron around the nucleus (Bohr model), in a plane. An orbital is the three-dimensional region around the nucleus where the probability of finding the electron is maximum (about 90%), obtained from the Schrödinger wave equation.

An orbit can hold \(2n^2\) electrons and does not follow the uncertainty principle; an orbital holds a maximum of 2 electrons and is consistent with the uncertainty principle.

Card 7

Whose theory or principle rules out the existence of definite paths or trajectories of electrons and other similar particles?

Answer: Heisenberg's uncertainty principle.

The two phenomena ______ and ______ can be explained by the wave nature of electromagnetic radiation.

Answer: interference and diffraction.

Write the four quantum numbers of the unpaired electron in the Cu atom in its ground state.

Answer: The unpaired electron is the 4s\(^1\) electron (Cu: [Ar] 3d\(^{10}\)4s\(^1\)): n = 4, l = 0, m = 0, s = +1/2 (or −1/2).

What values of the magnetic quantum number (m) are permitted for an electron having the angular quantum number l = 3?

Answer: m = −3, −2, −1, 0, +1, +2, +3 (that is, 2l + 1 = 7 values).

What values of the azimuthal quantum number (l) are permitted for an electron having the principal quantum number n = 4?

Answer: l = 0, 1, 2, 3.

Which sub-shells are not possible: 1p, 2s, 2p, 3d, 2d, 3f, 5g, 4f, 6h, 2f, 1d?

Answer: 1p, 2d, 3f, 2f and 1d are not possible, because l must be less than n (for example, n = 1 allows only l = 0). The others (2s, 2p, 3d, 5g, 4f, 6h) are possible.

The number of orbitals present in a given shell is: (4l + 2), (2l + 1), n\(^2\), 2n\(^2\).

Answer: \( n^2 \)

______ number of valence electrons are present in phosphorus.

Answer: 5 (3s\(^2\)3p\(^3\)).

The maximum number of emission lines observed when the excited electron of an H atom in n = 6 drops to the ground state is

Answer: \( \dfrac{n(n-1)}{2}=\dfrac{6\times5}{2}=15 \) lines.

Which has higher energy in a multi-electron atom: 3d or 4s?

Answer: 3d (it has n + l = 5, compared with 4 for 4s), so 4s is filled first.

Differentiate between the particle and wave character.

Answer: A particle has a definite position, mass and momentum and occupies a small, definite space; it can be located at a point. A wave is spread out in space and is described by its wavelength, frequency and amplitude; it shows interference and diffraction. Matter (e.g. the electron) and radiation show both characters (dual nature).

Card 8

The total number of orbitals associated with the principal quantum number n = 3 is ______.

Answer: 9 (\(n^2\): one 3s, three 3p and five 3d orbitals).

The energy of the 2s orbital of lithium is ______ (smaller, greater) than that of the 2s orbital of sodium.

Answer: greater. The 2s electrons of sodium feel a much larger nuclear charge (Z = 11), so they are more tightly bound (lower energy) than the 2s electrons of lithium (Z = 3).

Which is more paramagnetic and why: Zn\(^{2+}\), Fe\(^{2+}\), Fe\(^{3+}\), Cr\(^{3+}\)?

Answer: Fe\(^{3+}\), because it is 3d\(^5\) with 5 unpaired electrons (Fe\(^{2+}\) has 4, Cr\(^{3+}\) has 3 and Zn\(^{2+}\) has 0).

Which orbital electrons have the most imperfect screening (s, p, d, f)?

Answer: f electrons (the diffused shape of f orbitals shields the outer electrons from the nuclear charge least effectively).

Which shell would be the first to have a 'g' sub-shell?

Answer: The 5th shell (O shell, n = 5, since g corresponds to l = 4).

How many quantum numbers specify (i) an electron, (ii) an orbital? Name them.

(i) An electron is specified by four: n, l, m and s.
(ii) An orbital is specified by three: n, l and m.

The radius of the first stationary state, called the Bohr radius, is ______ pm.

Answer: 52.9 pm.

The visible spectrum ranges from ______ nm to ______ nm.

Answer: about 380 nm to 750 nm (roughly 400–700 nm).

The physical meaning of \( \psi^2 \) is ______.

Answer: The probability density: the probability of finding the electron per unit volume at a point.

When n = infinity, the energy of the electron is ______ J/atom.

Answer: Zero (the electron is free from the nucleus).

The lowest value of n that allows 'g' orbitals to exist is ______.

Answer: 5

Among the following pairs of orbitals, which orbital will experience the larger effective nuclear charge? (i) 2s and 3s, (ii) 4d and 4f, (iii) 3d and 3p, (iv) 2s and 2p.

(i) 2s
(ii) 4d
(iii) 3p
(iv) 2s

In each pair, the orbital which is closer to the nucleus or penetrates more (lower n, or lower l for the same n) experiences the larger effective nuclear charge.

Card 9

r\(_n\) = 52.9 × ______ pm.

Answer: \( r_n=52.9\times\dfrac{n^2}{Z}\ \text{pm} \)

The number of d-electrons remaining in the Fe\(^{2+}\) ion is (atomic number of Fe = 26).

Answer: Fe\(^{2+}\): [Ar] 3d\(^6\), so 6 d-electrons.

______ quantum number gives information about the spatial orientation of the orbital with respect to a standard set of co-ordinate axes.

Answer: The magnetic quantum number (m).

For the hydrogen atom, which has more energy: 4s or 3d?

Answer: 4s. In hydrogen (one electron) the energy depends only on n, so the 4s (n = 4) is higher than the 3d (n = 3).

Half-filled and fully filled degenerate sets of orbitals acquire extra stability due to ______ and ______.

Answer: symmetrical distribution of electrons and the exchange energy (more exchanges are possible between parallel-spin electrons).

An orbital contains a maximum of ______ electrons. This is the consequence of the ______ rule/principle.

Answer: 2 electrons; Pauli's exclusion principle.

______ orbitals are spherically symmetric and ______ orbitals are dumb-bell shaped.

Answer: s; p

______ quantum number tells about the size of the orbital and the energy of the electron.

Answer: The principal quantum number (n).

______ quantum number tells about the shape of orbitals.

Answer: The azimuthal quantum number (l).

______ series of lines of the hydrogen spectrum appears in the ultraviolet region of the electromagnetic spectrum.

Answer: The Lyman series.

The word 'aufbau' in German means ______.

Answer: 'building up'.

Card 10

The +2 oxidation state of which one is quite stable and why: Mn, Fe, Cr?

Answer: Mn. Mn\(^{2+}\) has the configuration 3d\(^5\), a half-filled d sub-shell, which has extra stability.

Which rule explains the three unpaired electrons present in the nitrogen atom?

Answer: Hund's rule of maximum multiplicity (2p\(^3\): one electron in each of the three 2p orbitals with parallel spins).

What is the difference between the 'L' and 'l' values for an electron present in one of the 4d orbitals?

Answer: For a 4d electron, l = 2 (the azimuthal quantum number). The orbital angular momentum is \( L=\sqrt{l(l+1)}\,\dfrac{h}{2\pi}=\sqrt6\,\dfrac{h}{2\pi} \), i.e. about 2.45 \( \hbar \). So l is a simple number (2) which fixes the shape, while L is the actual angular momentum of the electron.

For a given shell (n), the shielding effect is (arrange in decreasing order of sub-shells): ______.

Answer: s > p > d > f

Which electron is more tightly bound and why: 2s or 2p?

Answer: The 2s electron, because it penetrates closer to the nucleus (it has a non-zero probability near the nucleus), so it feels a larger effective nuclear charge and has lower energy than 2p.

______ is defined as the number of wavelengths per unit length.

Answer: Wave number (\( \bar\nu=1/\lambda \)).

The angular momentum (L) of a d-electron is ______.

Answer: \( \sqrt{l(l+1)}\dfrac{h}{2\pi}=\sqrt6\,\dfrac{h}{2\pi} \) (l = 2).

Atoms of different elements which possess the same number of neutrons are called ______.

Answer: isotones

The de Broglie wavelength of a tennis ball of mass 60 g moving with a velocity of 10 m/s is approximately ______ m.

Answer: \( \lambda=\dfrac{h}{mv}=\dfrac{6.626\times10^{-34}}{0.060\times10}\approx 1.1\times10^{-33}\ \text{m} \), far too small to be detected.

The value of the angular momentum of an electron in the 5th orbit according to Bohr's theory is ______.

Answer: \( \dfrac{5h}{2\pi}\approx 5.27\times10^{-34}\ \text{J s} \)

Differentiate between a proton and a photon.

Answer: A proton is a subatomic particle in the nucleus with rest mass \(1.67\times10^{-27}\) kg and charge +1.6\(\times10^{-19}\) C. A photon is a quantum (packet) of electromagnetic radiation, with zero rest mass, no charge, and always travels at the speed of light, with energy \(h\nu\).

Define the following / discuss briefly / state the following

Atomic number

Answer: The number of protons in the nucleus of an atom (equal to the number of electrons in a neutral atom). It is denoted by Z.

Spectrum

Answer: The pattern obtained when radiation is dispersed into its component wavelengths, e.g. a prism splits white light into a continuous spectrum of colours.

Isotopes

Answer: Atoms of the same element with the same atomic number but different mass numbers (different numbers of neutrons), e.g. \(^{35}\)Cl and \(^{37}\)Cl.

Isobars

Answer: Atoms of different elements having the same mass number but different atomic numbers, e.g. \(^{40}\)Ar and \(^{40}\)Ca.

Isotones

Answer: Atoms of different elements having the same number of neutrons, e.g. \(^{39}\)K and \(^{40}\)Ca.

Wavelength

Answer: The distance between two successive crests (or troughs) of a wave. It is denoted by \( \lambda \) and its SI unit is the metre.

Wavenumber

Answer: The number of waves per unit length, \( \bar\nu=1/\lambda \) (unit: m\(^{-1}\) or cm\(^{-1}\)).

Frequency

Answer: The number of waves passing a given point per second, \( \nu=c/\lambda \) (unit: hertz, s\(^{-1}\)).

Photoelectric effect

Answer: The emission of electrons from a metal surface when light of a suitable frequency (at least the threshold frequency) falls on it, e.g. from Cs, K. The kinetic energy of the electrons depends on the frequency, not the intensity, of the light: \( h\nu=h\nu_0+\tfrac12mv^2 \).

Quantum numbers

Answer: A set of numbers (n, l, m, s) which describe the size, shape, orientation and spin of an orbital and the electron in it.

Black body radiation

Answer: Radiation emitted by an ideal body that absorbs all the radiation falling on it. Planck explained its energy distribution by assuming that energy is emitted in packets (quanta), \( E=h\nu \).

de Broglie's duality

Answer: Matter (like electrons) also has wave character, with wavelength \( \lambda=h/mv \); so every moving particle shows both particle and wave properties.

Pauli's exclusion principle

Answer: No two electrons in an atom can have the same set of all four quantum numbers; an orbital holds a maximum of two electrons, with opposite spins.

Significance of the four quantum numbers

Answer: n gives the size and energy of the shell; l gives the shape of the orbital (sub-shell); m gives the orientation of the orbital in space; s gives the spin of the electron (+1/2 or −1/2).

Atomic spectra or line spectra

Answer: The spectrum of an atom, consisting of sharp lines of definite wavelengths, produced when an excited electron falls from a higher to a lower energy level; each element has its own line spectrum (a 'fingerprint').

Emission and absorption spectrum

Answer: The emission spectrum shows bright lines on a dark background and is formed by radiation emitted by excited atoms. The absorption spectrum shows dark lines at the same positions on a bright background, formed when atoms absorb those wavelengths from white light.

Heisenberg's uncertainty principle

Answer: It is impossible to determine simultaneously and exactly both the position and the momentum of a microscopic particle: \( \Delta x\cdot\Delta p\ge h/4\pi \).

Aufbau principle

Answer: Electrons fill the orbitals in the order of increasing energy (lowest energy first), using the \((n+l)\) rule: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, …

Hund's rule of maximum multiplicity

Answer: In degenerate orbitals, electrons occupy separate orbitals singly, with parallel spins, before any orbital gets a second electron.

Achievements of Bohr's theory

Answer: It explained the stability of the atom, the line spectrum of hydrogen and hydrogen-like ions (He\(^+\), Li\(^{2+}\)), and gave the radius and energy of the orbits, \( E_n=-13.6/n^2 \) eV, and the Rydberg constant.

Planck's quantum theory

Answer: Energy is emitted or absorbed by a body in discrete packets called quanta, each of energy \( E=h\nu \), where h is Planck's constant.

Radial and angular nodes

Answer: A radial node is a spherical surface at which the probability of finding the electron is zero; their number is \( n-l-1 \). An angular node is a plane or cone through the nucleus where the probability is zero; their number is \( l \). Total nodes = \( n-1 \).

Similarities and differences of the 1s and 2s orbitals

Answer: Both are spherical and have the same shape. 2s is larger and has higher energy than 1s; 2s has one radial node whereas 1s has none.

Effective nuclear charge

Answer: The net positive charge felt by an electron after the shielding by the other electrons: \( Z_{eff}=Z-\sigma \).

Work function

Answer: The minimum energy needed to remove an electron from the surface of a metal (\( W_0=h\nu_0 \)).

Degenerate orbitals

Answer: Orbitals having the same energy, e.g. the three 2p orbitals or the five 3d orbitals of an isolated atom.

Isoelectronic species

Answer: Atoms or ions having the same number of electrons, e.g. N\(^{3-}\), O\(^{2-}\), F\(^-\), Ne, Na\(^+\), Mg\(^{2+}\) (10 electrons each).

Shielding effect

Answer: The decrease in the attraction of the nucleus on the outer electrons due to the repulsion by the inner electrons. The order of shielding in a shell is s > p > d > f.

Isomer of hydrogen

Answer: Hydrogen exists as two nuclear spin isomers: ortho-hydrogen (the nuclear spins of the two protons are parallel) and para-hydrogen (the spins are antiparallel).

Cause of spectrum

Answer: Electrons jumping between energy levels: absorption of energy sends an electron to a higher level, and its return to a lower level emits radiation of frequency \( \nu=\Delta E/h \).

Isodiapheres and isosters

Answer: Isodiapheres are atoms with the same difference between the number of neutrons and protons (same \( n-p \)), e.g. \(^{39}\)K and \(^{19}\)F. Isosters are molecules or ions having the same number of atoms and the same number of electrons, e.g. CO\(_2\) and N\(_2\)O.

Shape of orbitals

Answer: s orbitals are spherical; p orbitals are dumb-bell shaped (three, along the x, y and z axes); d orbitals are mostly double dumb-bell (clover-leaf) shaped (five of them).

Energy of electrons in multi-electron and single-electron systems

Answer: In a single-electron system (H, He\(^+\)) the energy depends only on n (all orbitals of the same shell are degenerate). In multi-electron atoms the energy depends on both n and l (increases with \(n+l\)), because of the electron–electron repulsion and shielding.

Shortcomings of the Bohr and Rutherford models

Answer: Rutherford: the atom would be unstable, and it cannot explain the line spectrum. Bohr: it applies only to single-electron systems, cannot explain the fine structure or the Zeeman and Stark effects, and violates the uncertainty principle and the wave nature of the electron.

Characteristics of electromagnetic radiations

Answer: They consist of electric and magnetic fields oscillating perpendicular to each other and to the direction of travel; they need no medium; they travel at the speed of light (\(3\times10^8\) m/s in vacuum); they are characterised by wavelength, frequency, wavenumber and amplitude, and \( c=\nu\lambda \).

Bohr–Bury scheme

Answer: The rules for the distribution of electrons in the shells: the maximum number of electrons in a shell is \(2n^2\); the outermost shell holds at most 8 electrons and the next-to-outermost at most 18; electrons fill an outer shell only after the inner shells are filled in order.

Question. Assertion: The value of n for a line in Balmer series of hydrogen spectrum having the highest wave length is 4 and 6.
Reason: For Balmer series of hydrogen spectrum, the value n₁ = 2 and n₂ = 3, 4,5.
Answer : C

Question. Assertion: Absorption spectrum conists of some bright lines separated by dark spaces.
Reason: Emission spectrum consists of dark lines.
Answer : D

Question. Assertion: A resonance hybrid is always more stable than any of its canonical structures.
Reason: This stability is due to delocalization of electrons.
Answer : A

Question. Assertion: Cathode rays do not travel in straight lines.
Reason: Cathode rays penetrate through thick sheets
Answer : C

Question. Assertion: Electrons revolving around the nucleus do not fall into the nucleus because of centrifugal force.
Reason: Revolving electrons are planetary electrons.
Answer : B

Question. Assertion: The transition of electrons n₃ → n₂ in H atom will emit greater energy than n₄ → n₃ .
Reason: n₃ and n₂ are closer to nucleus tan n₄ .
Answer : B

Comprehension Based

Paragraph –I

The letters n, l, m proposed by Bohr, Sommerfeld and Zeeman respectively for quantization of angular momentum in classical physics were later on obtained as the results of solution of Schrodinger wave equation based on quantum mechanics. The term n, l, m were named as principal quantum number, azimuthal quantum number and magnetic quantum number respectively. The fourth quantum number s was given the name spin quantum number on the basis of two spins of electrons. 
The first two quantum numbers also decides the nodes of an orbital.

Question. The numerical value 4,3, 0 ψ denotes:
a. 3d-orbitals
b. 4f-orbitals
c. 2s-orbitals
d. 4d-orbitals
Answer : B

Question. The angular momentum of 3p-orbitals in terms of h(h = h/2π) is:
a. √2ℏ
b. 2ℏ
c. ℏ/√2
d. ℏ/2π
Answer : A

Question. Number of radial and angular nodes in 3p-orbitals respectively are:
a. 1, 1
b. 2, 1
c. 1, 2
d. 2, 2
Answer : A

Question. Which statement about energy level in H-atom is correct?
a. Only n and l decide energy level
b. Only ‘l’ decides energy level
c. Only n decides energy level
d. n, l and m decide energy level
Answer : C

Question. The quantum numbers of +½ and –½ for the electron spin represents:
a. rotation of electron in clockwise and anticlockwise direction respectively
b. rotation of electron in anticlockwise and clockwise direction respectively
c. two quantum mechanical states having classical analogue
d. two quantum mechanical states having no classical analogue
Answer : D

Paragraph –II

The hydrogen-like species Li²⁺ is in a spherically symmetric state S₁ with one radial node. Upon absorbing light the ion undergoes transition to a state S₂ . The state S₂ has one radial node and its energy is equal to the ground state energy of the hydrogen atom. 

Question. The state S₁ is:
a. 1s
b. 2s
c. 2p
d. 3s
Answer : B

Question. Energy of the state S₁ in units of the hydrogen atom ground state energy is:
a. 0.75
b. 1.50
c. 2.25
d. 4.50
Answer : C

Question. The orbital angular momentum quantum number of the state S₂ is:
a. 0
b. 1
c. 2
d. 3
Answer : B

Integer

Question. The angular momentum of electron in 2nd orbit of hydrogen atom is L. The angular momentum of electron in 4th orbit of hydrogen atom is n L where n =?
Answer : 2

Question. For an atom of an ion having single electron, the wavelength observed λ¹ = 2 are units and λ₃ = 2 units figure. The value of missing wavelength λ₂ is

Question. How many different wave-length may be observed in the spectrum from a hydrogen sample if the atoms are excited to 3rd excited state?
Answer : 6

Question. The work function (φ ) of some metals is listed below. The number of metals which will show photoelectric effect when light of 300 nm wavelength falls on the metal is
Metal   Li    Na     K    Mg   Cu    Ag   Fe    Pt     W
φ (eV) 2.4   2.3   2.2   3.7   4.8   4.3   4.7   6.3   4.75
Answer : 4

Please click the link below to download pdf file of CBSE Class 11 Chemistry Atomic Structure Flash Cards.