# NCERT solutions for Chemistry Part 1 and 2 Class 11 chapter 2 - Structure of Atom [Latest edition]

## Chapter 2: Structure of Atom

EXERCISES
EXERCISES [Pages 69 - 73]

### NCERT solutions for Chemistry Part 1 and 2 Class 11 Chapter 2 Structure of Atom EXERCISES [Pages 69 - 73]

EXERCISES | Q 2.1 - (i) | Page 69

Calculate the number of electrons which will together weigh one gram.

EXERCISES | Q 2.1 - (ii) | Page 69

Calculate the mass and charge of one mole of electrons.

EXERCISES | Q 2.2 - (i) | Page 69

Calculate the total number of electrons present in one mole of methane.

EXERCISES | Q 2.2 - (ii) | Page 69

Find (a) the total number and (b) the total mass of neutrons in 7 mg of 14C.
(Assume that mass of a neutron = 1.675 × 10–27 kg).

EXERCISES | Q 2.2 - (iii) | Page 69

Find (a) the total number and (b) the total mass of protons in 34 mg of NH3 at STP. Will the answer change if the temperature and pressure are changed?

EXERCISES | Q 2.3 | Page 69

How many neutrons and protons are there in the following nuclei?

""_6^13"C", ""_8^16"O", ""_12^24"Mg", ""_26^56"Fe", ""_38^88"Sr"

EXERCISES | Q 2.4 - (i) | Page 69

Write the complete symbol for the atom with the given atomic number (Z) and Atomic mass (A)

Z = 17, A = 35

EXERCISES | Q 2.4 - (ii) | Page 69

Write the complete symbol for the atom with the given atomic number (Z) andAtomic mass (A).

Z = 92, A = 233

EXERCISES | Q 2.4 - (iii) | Page 69

Write the complete symbol for the atom with the given atomic number (Z) and atomic mass (A).

Z = 4, A = 9

EXERCISES | Q 2.5 | Page 69

Yellow light emitted from a sodium lamp has a wavelength (λ) of 580 nm. Calculate the frequency (ν) and wave number (bar v) of the yellow light.

EXERCISES | Q 2.6 - (i) | Page 69

Find energy of each of the photons which correspond to light of frequency 3 × 1015 Hz.

EXERCISES | Q 2.6 - (ii) | Page 69

Find energy of each of the photons which have the wavelength of 0.50 Å.

EXERCISES | Q 2.7 | Page 69

Calculate the wavelength, frequency and wave number of a light wave whose period is 2.0 × 10-10s.

EXERCISES | Q 2.8 | Page 69

What is the number of photons of light with a wavelength of 4000 pm that provide 1 J of energy?

EXERCISES | Q 2.9 | Page 69

A photon of wavelength 4 × 10–7 m strikes on the metal surface, the work function of the metal being 2.13 eV. Calculate

1. the energy of the photon (eV),
2. the kinetic energy of the emission, and
3. the velocity of the photoelectron (1 eV = 1.6020 × 10–19 J).
EXERCISES | Q 2.10 | Page 69

Electromagnetic radiation of wavelength 242 nm is just sufficient to ionise the sodium atom. Calculate the ionisation energy of sodium in kJ mol–1.

EXERCISES | Q 2.11 | Page 69

A 25-watt bulb emits monochromatic yellow light of the wavelength of 0.57μm. Calculate the rate of emission of quanta per second.

EXERCISES | Q 2.12 | Page 69

Electrons are emitted with zero velocity from a metal surface when it is exposed to radiation of wavelength 6800 Å. Calculate threshold frequency (v0) and work function (W0) of the metal.

EXERCISES | Q 2.13 | Page 69

What is the wavelength of light emitted when the electron in a hydrogen atom undergoes a transition from an energy level with n = 4 to an energy level with n = 2?

EXERCISES | Q 2.14 | Page 70

How much energy is required to ionise an H atom if the electron occupies n = 5 orbit? Compare your answer with the ionization enthalpy of H atom (energy required to remove the electron from n =1 orbit).

EXERCISES | Q 2.15 | Page 70

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

EXERCISES | Q 2.16 - (i) | Page 70

The energy associated with the first orbit in the hydrogen atom is - 2.18 × 10-18 J atom-1. What is the energy associated with the fifth orbit?

EXERCISES | Q 2.16 - (ii) | Page 70

Calculate the radius of Bohr’s fifth orbit for hydrogen atom

EXERCISES | Q 2.17 | Page 70

Calculate the wave number for the longest wavelength transition in the Balmer series of atomic hydrogen.

EXERCISES | Q 2.18 | Page 70

What is the energy in joules, required to shift the electron of the hydrogen atom from the first Bohr orbit to the fifth Bohr orbit and what is the wavelength of the light emitted when the electron returns to the ground state? The ground state electron energy is –2.18 × 10–11 ergs.

EXERCISES | Q 2.19 | Page 70

The electron energy in the hydrogen atom is given by En = (–2.18 × 10–18)/n2 J. Calculate the energy required to remove an electron completely from the n = 2 orbit. What is the longest wavelength of light in cm that can be used to cause this transition?

EXERCISES | Q 2.20 | Page 70

Calculate the wavelength of an electron moving with a velocity of 2.05 × 107 ms-1.

EXERCISES | Q 2.21 | Page 70

The mass of an electron is 9.1 × 10–31 kg. If its K.E. is 3.0 × 10–25 J, calculate its wavelength.

EXERCISES | Q 2.22 | Page 70

Which of the following are isoelectronic species i.e., those having the same number of electrons?

Na+, K+, Mg2+, Ca2+, S2–, Ar

EXERCISES | Q 2.23 - (i) (a) | Page 70

Write the electronic configurations of the given ions H.

EXERCISES | Q 2.23 - (i) (b) | Page 70

Write the electronic configurations of the given ions Na+.

EXERCISES | Q 2.23 - (i) (c) | Page 70

Write the electronic configurations of the given ions O2–.

EXERCISES | Q 2.23 - (i) (d) | Page 70

Write the electronic configurations of the given ions F.

EXERCISES | Q 2.23 - (ii) (a) | Page 70

What are the atomic numbers of elements whose outermost electrons is represented by 3s1.

EXERCISES | Q 2.23 - (ii) (b) | Page 70

What are the atomic numbers of elements whose outermost electrons is represented by 2p3.

EXERCISES | Q 2.23 - (ii) (c) | Page 70

What are the atomic numbers of elements whose outermost electrons is represented by 3p5?

EXERCISES | Q 2.23 - (iii) (a) | Page 70

Which atom is indicated by the following configuration?

[He] 2s1

EXERCISES | Q 2.23 - (iii) (b) | Page 70

Which atom is indicated by the following configuration?

[Ne] 3s2 3p3

EXERCISES | Q 2.23 - (iii) (c) | Page 70

Which atom is indicated by the following configuration?

[Ar] 4s2 3d1.

EXERCISES | Q 2.24 | Page 70

What is the lowest value of n that allows g orbitals to exist?

EXERCISES | Q 2.25 | Page 70

An electron is in one of the 3d orbitals. Give the possible values of n, l and ml for this electron.

EXERCISES | Q 2.26 | Page 70

An atom of an element contains 29 electrons and 35 neutrons. Deduce (i) the number of protons and (ii) the electronic configuration of the element.

EXERCISES | Q 2.27 | Page 70

Give the number of electrons in the species "H"_2^+, Hand "O"_2^+

EXERCISES | Q 2.28 - (i) | Page 70

An atomic orbital has n = 3. What are the possible values of l and ml?

EXERCISES | Q 2.28 - (ii) | Page 70

List the quantum numbers (ml and l) of electrons for 3d orbital.

EXERCISES | Q 2.28 - (iii) | Page 70

Which of the following orbitals are possible?

1p, 2s, 2p and 3f

EXERCISES | Q 2.29 - (a) | Page 70

Using s, p, d notations, describe the orbital with the following quantum numbers n = 1, l = 0.

EXERCISES | Q 2.29 - (b) | Page 70

Using s, p, d notations, describe the orbital with the following quantum numbers n = 3; l =1.

EXERCISES | Q 2.29 - (c) | Page 70

Using s, p, d notations, describe the orbital with the following quantum numbers n = 4; l = 2.

EXERCISES | Q 2.29 - (d) | Page 70

Using s, p, d notations, describe the orbital with the following quantum numbers n = 4; l =3.

EXERCISES | Q 2.30 | Page 70

Explain, giving reasons, which of the following sets of quantum numbers are not possible.

(a) n = 0, l = 0, ml = 0, ms = + ½

(b) n = 1, l = 0, ml = 0, ms = – ½

(c) n = 1, l = 1, ml = 0, ms = + ½

(d) n = 2, l = 1, ml = 0, ms = – ½

(e) n = 3, l = 3, ml = –3, ms = + ½

(f) n = 3, l = 1, ml = 0, ms = + ½

EXERCISES | Q 2.31 - (a) | Page 71

How many electrons in an atom may have the following quantum numbers?

n = 4, m_s =  -1/2

EXERCISES | Q 2.31 - (b) | Page 71

How many electrons in an atom may have the following quantum numbers?

n = 3, l = 0

EXERCISES | Q 2.32 | Page 71

Show that the circumference of the Bohr orbit for the hydrogen atom is an integral multiple of the de Broglie wavelength associated with the electron revolving around the orbit.

EXERCISES | Q 2.33 | Page 71

What transition in the hydrogen spectrum would have the same wavelength as the Balmer transition n = 4 to n = 2 of He+ spectrum?

EXERCISES | Q 2.34 | Page 71

Calculate the energy required for the process

$\ce{He^+_{(g)} -> He^{2+}_{(g)} + e^-}$

The ionization energy for the H atom in the ground state is 2.18 ×10–18 J atom–1

EXERCISES | Q 2.35 | Page 71

If the diameter of a carbon atom is 0.15 nm, calculate the number of carbon atoms which can be placed side by side in a straight line across the length of scale of length 20 cm long.

EXERCISES | Q 2.36 | Page 71

2 × 108 atoms of carbon are arranged side by side. Calculate the radius of carbon atom if the length of this arrangement is 2.4 cm.

EXERCISES | Q 2.37 | Page 71

The diameter of zinc atom is 2.6 Å. Calculate

1. radius of zinc atom in pm and
2. number of atoms present in a length of 1.6 cm if the zinc atoms are arranged side by side length-wise.
EXERCISES | Q 2.38 | Page 71

A certain particle carries 2.5 × 10-16 C of static electric charge. Calculate the number of electrons present in it.

EXERCISES | Q 2.39 | Page 71

In Milikan’s experiment, static electric charge on the oil drops has been obtained by shining X-rays. If the static electric charge on the oil drop is - 1.282 × 10-18C, calculate the number of electrons present on it.

EXERCISES | Q 2.40 | Page 71

In Rutherford’s experiment, generally the thin foil of heavy atoms, like gold, platinum etc. have been used to be bombarded by the α-particles. If the thin foil of light atoms like aluminium etc. is used, what difference would be observed from the above results?

EXERCISES | Q 2.41 | Page 71

Symbols ""_35^79"Br" and ""^79"Br" can be written, whereas symbols ""_79^35"Br" and ""^35"Br" are not acceptable. Answer briefly.

EXERCISES | Q 2.42 | Page 71

An element with mass number 81 contains 31.7% more neutrons as compared to protons. Assign the atomic symbol.

EXERCISES | Q 2.43 | Page 71

An ion with mass number 37 possesses one unit of negative charge. If the ion contains 11.1% more neutrons than the electrons, find the symbol of the ion.

EXERCISES | Q 2.44 | Page 71

An ion with mass number 56 contains 3 units of positive charge and 30.4% more neutrons than electrons. Assign the symbol to this ion.

EXERCISES | Q 2.45 | Page 71

Arrange the following type of radiations in increasing order of frequency:

2. amber light from traffic signal
4. cosmic rays from outer space and
5. X-rays.
EXERCISES | Q 2.46 | Page 71

Nitrogen laser produces radiation at a wavelength of 337.1 nm. If the number of photons emitted is 5.6 × 1024, calculate the power of this laser.

EXERCISES | Q 2.47 | Page 71

Neon gas is generally used in the signboards. If it emits strongly at 616 nm, calculate

1. the frequency of emission,
2. distance traveled by this radiation in 30 s
3. energy of quantum and
4. number of quanta present if it produces 2 J of energy.
EXERCISES | Q 2.48 | Page 72

In astronomical observations, signals observed from the distant stars are generally weak. If the photon detector receives a total of 3.15 × 10–18 J from the radiations of 600 nm, calculate the number of photons received by the detector.

EXERCISES | Q 2.49 | Page 72

Lifetimes of the molecules in the excited states are often measured by using pulsed radiation source of duration nearly in the nanosecond range. If the radiation source has a duration of 2 ns and the number of photons emitted during the pulse source is 2.5 × 1015, calculate the energy of the source.

EXERCISES | Q 2.50 | Page 72

The longest wavelength doublet absorption transition is observed at 589 and 589.6 nm. Calculate the frequency of each transition and energy difference between two excited states.

EXERCISES | Q 2.51 | Page 72

The work function for caesium atom is 1.9 eV. Calculate

1. the threshold wavelength and
2. the threshold frequency of the radiation. If the caesium element is irradiated with a wavelength 500 nm, calculate the kinetic energy and the velocity of the ejected photoelectron.
EXERCISES | Q 2.52 | Page 72

Following results are observed when sodium metal is irradiated with different wavelengths. Calculate (a) threshold wavelength and, (b) Planck’s constant.

 λ (nm) 500 450 400 v × 10-5 (cm s-1) 2.55 4.35 5.35
EXERCISES | Q 2.53 | Page 72

The ejection of the photoelectron from the silver metal in the photoelectric effect experiment can be stopped by applying the voltage of 0.35 V when the radiation 256.7 nm is used. Calculate the work function for silver metal.

EXERCISES | Q 2.54 | Page 72

If the photon of the wavelength 150 pm strikes an atom and one of its inner bound electrons is ejected out with a velocity of 1.5 × 107 ms–1, calculate the energy with which it is bound to the nucleus.

EXERCISES | Q 2.55 | Page 72

Emission transitions in the Paschen series end at orbit n = 3 and start from orbit n and can be represented as v = 3.29 × 1015 (Hz) [1/32 – 1/n2]

Calculate the value of n if the transition is observed at 1285 nm. Find the region of the spectrum.

EXERCISES | Q 2.56 | Page 72

Calculate the wavelength for the emission transition if it starts from the orbit having radius 1.3225 nm and ends at 211.6 pm. Name the series to which this transition belongs and the region of the spectrum.

EXERCISES | Q 2.57 | Page 72

Dual behaviour of matter proposed by de Broglie led to the discovery of electron microscope often used for the highly magnified images of biological molecules and other type of material. If the velocity of the electron in this microscope is 1.6 × 106 ms–1, calculate de Broglie wavelength associated with this electron.

EXERCISES | Q 2.58 | Page 72

Similar to electron diffraction, neutron diffraction microscope is also used for the determination of the structure of molecules. If the wavelength used here is 800 pm, calculate the characteristic velocity associated with the neutron.

EXERCISES | Q 2.59 | Page 72

If the velocity of the electron in Bohr’s first orbit is 2.19 × 106 ms-1, calculate the de Broglie wavelength associated with it.

EXERCISES | Q 2.60 | Page 72

The velocity associated with a proton moving in a potential difference of 1000 V is 4.37 × 105 ms–1. If the hockey ball of mass 0.1 kg is moving with this velocity, calculate the wavelength associated with this velocity.

EXERCISES | Q 2.61 | Page 72

If the position of the electron is measured within an accuracy of ± 0.002 nm, calculate the uncertainty in the momentum of the electron. Suppose the momentum of the electron is h/4πm × 0.05 nm, is there any problem in defining this value.

EXERCISES | Q 2.62 | Page 72

The quantum numbers of six electrons are given below. Arrange them in order of increasing energies. If any of these combination(s) has/have the same energy lists:

1. n = 4, l = 2, ml = –2 , ms = - 1/2
2. n = 3, l = 2, ml= 1 , ms = +1/2
3. n = 4, l = 1, ml = 0 , ms = +1/2
4. n = 3, l = 2, ml = –2 , ms = –1/2
5. n = 3, l = 1, ml = –1 , ms= +1/2
6. n = 4, l = 1, ml = 0 , ms = +1/2
EXERCISES | Q 2.63 | Page 73

The bromine atom possesses 35 electrons. It contains 6 electrons in 2p orbital, 6 electrons in 3p orbital and 5 electrons in 4p orbital. Which of these electron experiences the lowest effective nuclear charge?

EXERCISES | Q 2.64 | Page 73

Among the following pairs of orbitals which orbital will experience the larger effective nuclear charge?

1. 2s and 3s,
2. 4d and 4f,
3. 3d and 3p
EXERCISES | Q 2.65 | Page 73

The unpaired electrons in Al and Si are present in 3p orbital. Which electrons will experience more effective nuclear charge from the nucleus?

EXERCISES | Q 2.66 - (a) | Page 73

Indicate the number of unpaired electrons in a P.

EXERCISES | Q 2.66 - (b) | Page 73

Indicate the number of unpaired electrons in Si.

EXERCISES | Q 2.66 - (c) | Page 73

Indicate the number of unpaired electrons in Cr.

EXERCISES | Q 2.66 - (d) | Page 73

Indicate the number of unpaired electrons in Fe.

EXERCISES | Q 2.66 - (e) | Page 73

Indicate the number of unpaired electrons in Kr.

EXERCISES | Q 2.67 - (a) | Page 73

How many sub-shells are associated with n = 4?

EXERCISES | Q 2.67 - (b) | Page 73

How many electrons will be present in the sub-shells having ms value of - 1/2 for n = 4?

EXERCISES

## NCERT solutions for Chemistry Part 1 and 2 Class 11 chapter 2 - Structure of Atom

NCERT solutions for Chemistry Part 1 and 2 Class 11 chapter 2 (Structure of Atom) include all questions with solution and detail explanation. This will clear students doubts about any question and improve application skills while preparing for board exams. The detailed, step-by-step solutions will help you understand the concepts better and clear your confusions, if any. Shaalaa.com has the CBSE Chemistry Part 1 and 2 Class 11 solutions in a manner that help students grasp basic concepts better and faster.

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Concepts covered in Chemistry Part 1 and 2 Class 11 chapter 2 Structure of Atom are Discovery of Electron, Charge to Mass Ratio of Electron, Charge on the Electron, Discovery of Protons and Neutrons, Concept of Atomic Models, J. J. Thomson’s Atomic Model, Lord Rutherford’s Atomic model, Atomic Number (Z), Mass Number (A), and Number of Neutrons (n), Isobars, Isotopes, Drawbacks of Rutherford Atomic Model, Wave Nature of Electromagnetic Radiation, Particle Nature of Electromagnetic Radiation: Planck's Quantum Theory of Radiation, Evidence for the Quantized Electronic Energy Levels - Atomic Spectra, Dual Behaviour of Matter: De Broglie's relationship, Heisenberg’s Uncertainty Principle, Quantum Mechanical Model of the Atom - Orbitals and Quantum Numbers, Quantum Mechanical Model of the Atom - Concept of Shells and Subshells, Quantum Mechanical Model of the Atom - Shapes of Atomic Orbitals, Quantum Mechanical Model of the Atom - Energies of Orbitals, Quantum Mechanical Model of the Atom - Filling of Orbitals in Atom, Quantum Mechanical Model of the Atom - Electronic Configuration of Atoms, Quantum Mechanical Model of the Atom - Stability of Completely Filled and Half Filled Subshells, Atomic Mass, Bohr’s Model for Hydrogen Atom, Quantum Mechanical Model of Atom, Electromagnetic Waves : Numericals, Structure of Atom Numericals.

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