Structure of Atom - Online Test

# Structure of Atom # CBSE 11TH CHEMISTRY Prepare / Learn

Q1. Emission spectrum of a material results from the material's (atom or molecules)

A. transition from excited to normal state

B. transition from normal to excited state

C. radiating an inverted spectrum

D. radiating a continuous spectrum

Answer : Option A
Explaination / Solution:

The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to an atom or molecule making a transition from a high energy state to a lower energy state. The photon energy of the emitted photon is equal to the energy difference between the two states. There are many possible electron transitions for each atom, and each transition has a specific energy difference. This collection of different transitions, leading to different radiated wavelengths, make up an emission spectrum.

# Structure of Atom # CBSE 11TH CHEMISTRY Prepare / Learn

Q2. Absorption spectrum, seen as dark lines in an otherwise continuous spectrum, for a given material results from the material's (atom or molecules)

A. absorbing selected wavelengths from an input of continuous spectrum

B. absorbing selected wavelengths and returning to normal ground state

C. absorbing all wavelengths and returning to normal ground state

D. absorbing all wavelengths from an input of continuous spectrum

Answer : Option A
Explaination / Solution:

In an absorption spectrum, portions of a continuous spectrum (light containing all wavelengths) are missing because they have been absorbed by the medium through which the light has passed; the missing wavelengths appear as dark lines or gaps.

# Structure of Atom # CBSE 11TH CHEMISTRY Prepare / Learn

Q3. When an electric discharge is passed through gaseous hydrogen, the H2 molecules dissociate and the energetically excited hydrogen atoms produced emit electromagnetic radiation of discrete frequencies. The hydrogen spectrum consists of

A. several lines named after their discoverers

B. several series of lines named after their discoverers

C. a continuous spectrum that reduces to zero at large wavelengths

D. a continuous spectrum that reduces to zero at small wavelengths

Answer : Option B
Explaination / Solution:

The emission spectrum of hydrogen consists of several series of sharp emission lines in the ultraviolet (Lyman series). in the visible (Balmer series). and in the infrared (Paschen series, Brackett series, etc,) regions of the spectrum. These series are named after their discoverer.

# Structure of Atom # CBSE 11TH CHEMISTRY Prepare / Learn

Q4. Consider the ground state of Cr atom (Z = 24). The numbers of electrons with the azimuthal quantum numbers, l = 1 and 2 are, respectively:

A. 16 and 5

B. 16 and 4

C. 12 and 4

D. 12 and 5

Answer : Option D
Explaination / Solution:

Azimuthal quantum number l = 1 is for p and l = 2 is for d.

Now Cr has configuration $1 s^{2}, 2 s^{2}, 2 p^{6}, 3 s^{2}, 3 p^{6}, 3 d^{5}, 4 s^{1}$

Hence there are 12, p-electrons and 5, d-electrons

# Structure of Atom # CBSE 11TH CHEMISTRY Prepare / Learn

Q5.

Mg2+ is isoelectronic with

K+

Cu2+

Zn2+

D. NA+

Answer : Option D
Explaination / Solution:

Isoelectronic species refers to the elements that have the same number of electrons.

Mg2+ is a 10 electron species $(1 s^{2}, 2 s^{2}, 2 p^{6})$ .Its configuration is like that of Ne.

Thus it is isoelectronic with any element having 10e- or we can say 8e- in its valence shell.

Atomic number of Sodium (Na) is 11 after loosing one electron it became Na+ and have 10 electron.

Thus Mg2+ is isoelectronic with Na+.

# Structure of Atom # CBSE 11TH CHEMISTRY Prepare / Learn

Q6. According to the Heisenberg uncertainty principle, in dealing with milligram-sized or heavier objects,

A. the associated uncertainties are very important

B. the associated uncertainties are unacceptable

C. the associated uncertainties are hardly of any real consequence

D. there are no uncertainties at all

Answer : Option C
Explaination / Solution:

The effect of Heisenberg uncertainty principle is significant only for motion of microscopic objects, it is negligible in case of macroscopic objects. For example, we apply the concept of uncertainty to an object of mass 1 milligram.

$Δ x \times ∆ v_{x} = \frac{h}{4 π m}$

$= \frac{6.626 \times 10^{- 34}}{4 \times 3.1416 \times 10^{- 6}} \approx 10^{- 28} m^{2} s^{- 1}$

The value of $∆ x ∆ v_{x}$ is very small and insignificant in this case. Therefore, when we deal with heavier objects the associated uncertainties have no real consequences and can be neglected.

# Structure of Atom # CBSE 11TH CHEMISTRY Prepare / Learn

Q7. Quantum mechanics is a theoretical science that deals with the study of the

A. motions of the microscopic objects that have both observable wave like and particle like properties

B. motions of the macroscopic objects that have only particle like properties

C. motions of the macroscopic objects that have both observable wave like and particle like properties

D. motions of the microscopic objects that have only particle like properties

Answer : Option A
Explaination / Solution:

quantum mechanics, science dealing with the behaviour of matter and light on the atomic and subatomic scale. It attempts to describe and account for the properties of molecules and atoms and their constituents—electrons, protons, neutrons, and other more esoteric particles such as quarks and gluons. These properties include the interactions of the particles with one another and with electromagnetic radiation (i.e., light, X-rays, and gamma rays).

# Structure of Atom # CBSE 11TH CHEMISTRY Prepare / Learn

Q8. According to quantum theoretical model of an atom each orbital is designated by three quantum numbers labelled as n, l and ml. These are referred to respectively as

A. Azimuthal quantum number or orbital angular momentum, Principal quantum number, and Magnetic orbital quantum number.

B. Principal quantum number, Azimuthal quantum number or orbital angular momentum and Magnetic orbital quantum number.

C. Azimuthal quantum number or orbital angular momentum, Principal quantum number, and spin quantum number.

D. Principal quantum number, Azimuthal quantum number or orbital angular momentum and spin quantum number

Answer : Option B
Explaination / Solution:

Quantum numbers designate specific shells, subshells, orbitals, and spins of electrons. This means that they describe completely the characteristics of an electron in an atom, i.e., they describe each unique solution to the Schrödinger equation, or the wave function, of electrons in an atom. There are a total of four quantum numbers: the principal quantum number (n), the orbital angular momentum quantum number (l), the magnetic quantum number (ml), and the electron spin quantum number (ms). The principal quantum number, nn , describes the energy of an electron and the most probable distance of the electron from the nucleus. In other words, it refers to the size of the orbital and the energy level an electron is placed in. The number of subshells, or ll , describes the shape of the orbital. It can also be used to determine the number of angular nodes. The magnetic quantum number, ml, describes the energy levels in a subshell, and ms refers to the spin on the electron, which can either be up or down.

# Structure of Atom # CBSE 11TH CHEMISTRY Prepare / Learn

Q9. According to quantum theoretical model of an atom each orbital is designated by three quantum numbers labelled as n, l and ml. The values these can take are

n = 1,2,3..
l= 0,1,..n;
m = -l,-l+1, ..0,1..l-1, l

n = 1,2,3..
l= 0,1,..n
m= -l,-l+1, ..0,1

n = 1,2,3..
l= 0,1,..n-1;
m = 0,1..l-1, l

n = 1,2,3..
l= 0,1,..n-1;
mI = -I,-I+1,..0,1..I-1,I

Answer : Option D
Explaination / Solution:

n (Principal quantum number) value tell about the shell to which the electro belong, Ex,If n=1 electron belongs to first shell (K) around the nucleus

l (Azimuthal quantum number) tell about angular momentum, and shape of the orbitals, and it designates the subshells to which the electron belongs to. For a given value of 'n', ' l' can have value ranging from 0 to n-1. Ex, If n=2 then , the value of 'l' will be 0 and 1 (0 to n-1)

ml ( Magnetic orbital quantum number) determines the number of preferred orientations of the orbitals in the subshell, which are defined by given 'l' value. ex if 'l'= 2 then ml = 2l+1 =2*2 +1= 5 m value ie., m = +2,+1,0,-2,-1

# Structure of Atom # CBSE 11TH CHEMISTRY Prepare / Learn

Q10. spin quantum number with two spin states of the electron represented by two arrows, ↑ (spin up) and ↓ (spin down) was introduced to account for

A. to account for uncertainty in electron states

B. the splitting of emission lines in an electric field

C. the splitting of emission lines in a Magnetic field

D. the splitting of emission lines in vacuum

Answer : Option C
Explaination / Solution:

In 1920, Otto Stern and Walter Gerlach designed an experiment, which unintentionally led to the discovery that electrons have their own individual, continuous spin even as they move along their orbital of an atom. The experiment mentioned above by Otto Stern and Walter Gerlach was done with silver which was put in an oven and vaporized. The result was that silver atoms formed a beam that passed through a magnetic field in which it split in two.

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