Questions From: Atomic Structure Chemical Bonding and Solutions Chapter
1. According to Bohr's theory, the orbits in which electrons move are- circular
Explanation: According to Bohr's atomic model, electrons move around the nucleus at certain and definite energy levels represented as n=1,2,3,.. and electrons revolves around the nucleus in circular orbit.
2.Rutherford's experiment on scattering of alpha particles showed for the first time that the atom has- nucleus
Explanation: Rutherford observed tha the positively charged a-particles were repelled and deflected by the positive charges in the atom.Rutherford's named this positively charged portion of atom as nucleus.
3. In Rutherford's experiments of atomic model the screen behind the gold foil contains- ZnS
Explanation: Zinc sulphide (ZnS) is employed in a - ray scattering experiments because of its ability to produce light flashes after colliding with an a particle.
4. How many atomic orbitals are present in the forth energy level of an atom? - 16
Explanation: Total number of orbitals present in any given energy level = n?. Hence total number of orbitals present in 4th energy level is = 42 = 16.
5. For M-shell the total number of electron is- 18
Explanation: The maximum no. of electrons = 2n² Where n denotes the shell number. For M, the value of n = 3, So no of electrons = 2x32=18 Therefore, the M shell can hold a maximum of 18 electrons, but if it is the outermost shell, then it cannot hold more than 8 electrons.
6. An orbital can accommodate maximum _2_ number of electrons.
Explanation: According to Pauli's Exclusion principle and spin quantum number, every orbital can have a maximum of 2 electrons only.
7.Which quantum number represents shape of an orbital ? - Azimuthal
Explanation: Principal quantum number determines size of the orbital. Magnetic quantum number determines orientation of the orbital. Azimuthal quantum number determines shape of the orbital.
8.Which quantum number indicates shell number? -Principle
Explanation: The principal quantum number, n, designates the principal electron shell. Because n describes the most probable distance of the electrons from the nucleus.
9.Which of the following quantum numbers governs the spatial orientation of an atomic orbital? -Magnetic quantum number
Explanation: The magnetic quantum number describes the spatial orientation or distribution of electron cloud. The spin quantum number represents the direction of electron spin around its own axis.
10.The ion which contains 8 electrons in the outermost shell is- O2-
Explanation: The atomic number of O = 8 So, number of electrons = 8 Number of electrons in 02- are 8+2=10 Electronic configuration: 1s2 2s2 2p6 :. Electron in outermost shell= 2+6 = 8
11.Maximum number of lectrons that can be accommodate in d sub-shell is-10
Explanation: Maximum number of electrons held in the d orbitals is 10. There are 5 sub-levels in a d orbital, each one can have a maximum 2 electrons. Hence, 5 sub-levels can have a maximum of 10 electrons. Thus, , p, d and f orbitals can accommodate a maximum of 2, 6, 10 an 14 electrons respectively.
12.The ion which contains d electron is-Cr3+
Explanation: The electronic configuration of Cr is 1s2 2s² 2p6 3s2 3p6 3d³
13.The number of electrons in the d orbital of an atom of chromium of atomic number 24 is-5
Explanation: 'The electronic configuration of Cr is 1s2 2s2 2p6 3s2 3p6 3d5 4s1 :. total s-orbitals=4 total p-orbitals=6 total d-orbitals=5
14.The number of proton in Ca2+ ? - 18
Explanation: Calcium (Ca) has the atomic number of 20, so every atom of calcium contains 20 2+ protons.Ca has a deficiency of electrons relative to protons. Since the charge on this ion is +2, we have 18 electrons.
15.Which one is isotope? -6c12, 6c13
Explanation: 6C12 and C13 possess the same number of protons and electrons, but a different number of neutrons so they are isotope.
16.Which one has radioactive isotopes?-uranium
Explanation: The best known example of a naturally-occurring radioisotope is uranium. All but 0.7 per cent of naturally-occurring uranium is uranium-238; the rest is the less stable, or more radioactive, uranium-235, which has three fewer neutrons in its nucleus.
17.The effective number of Na' and Cl- each ion in the unit cell is-4
Explanation: Number of chloride ions in the unit cell -8×1/8+6×1/2=1+3=4 Number of sodium ions in the unit cell =12×1/4+1×1/1 =3+1=4
18.Hybridisation of C in CH4 is- sp³
Explanation: The carbon atom in methane (CH,) has sp3 hybridization. The four hydrogen atoms use the carbon's sp3 hybrid orbitals to form C-H sigma bonds, which creates the methane molecule,
19.The hybridization of 'B' in BCl3, is-sp²
Explanation: The type of hybridization that occurs in BCl3 is sp² hybridization. In BCI3 molecule, boron will be the central atom which contains three bonded atoms but no lone pair of electrons. Its steric number is also said to be 3.
20.The bond angle of sp² hybridized orbital is- 120°
Explanation: An sp² hybridized atomic orbital is the mixing of 1s orbital and 2p orbitals. It has 3ơ bond so its molecular geometry is trigonal with 120° bond angles.
21.Which elements exhibit maximum number of valence electrons? - Phosphorus (P)
Explanation: Sodium belongs to group 1 and has 1 valence electron. Aluminium belongs to group 13 and has 3 valence electrons. Silicon belongs to group 14 and has 4 valence electrons. Lastly, phosphorus belongs to group 15 and has 5 valence electrons. Hence we can see that phosphorus has the maximum number of valence electrons.
22.High boiling point of water is due to-H-bond
Explanation: Higher boiling point of water is due to hydrogen bonding. Several water molecules associate through H-bonding. Large amount of energy is required to break this association
23.Crystalline variety of carbon allotropy is- diamond
Explanation: The crystalline forms have definite geometrical shapes and regular arrangements of atoms in their structure. Among the allotropes of carbon, diamond is crystalline.
24.Number of coordinate bond in 03 molecule is- 1
Explanation: The ozone molecule contains three oxygen atoms: The center oxygen atom makes a double bond ith one oxygen atom in this structure but gives two electrons to the other oxygen atom to create a coordinate bond. As a result,03 has one coordinate bond.
25.In graphite, the layers are held by force called- Van der walls
Explanation: Graphite contains layers of carbon atoms. The layers slide over each other easily because there are only weak forces such as Van der Walls force between them, which makes graphite slippery.
26.The C-C bond length is maximum in-Diamond
Explanation: Diamond has the longest C-C bond length because it has a purely single bond, while graphite and Co and C7o have C-C bonds with a doubled bond character.
27.Very low density of ice compare to water is due to- Hydrogen bonding
Explanation: When ice is formed, there remain empty spaces in the structure of ice. These empty spaces are due to the directional hydrogen bonds. H20 forms a cage-like structure in solid ice and density is reduced.
28.In ice, arrangement of H20 molecule is-Tetrahedral
Explanation: In ice, four hydrogen bonds optimally arrange themselves tetrahedrally around each water molecule as found in ordinary ice.
29.The primary standard solution is -K2Cr207
Explanation: 'The primary standard is a compound of sufficient purity from which standard solutions of known normalities can be prepared by direct weighing of it and diluting to a defined volume of solution. Potassium Dichromate (K2Cr207) is suitable to be used as a primary standard.
30.The secondary standard solution is-HCI
Explanation: A secondary standard solution is a chemical term that refers to a solution that has its concentration measured by titration with a primary standard solution. For example, making a primary standard solution of Na2CO3 and then titrating that to find the accurate concentration of HCI will ake the HCI solution econdary standard.
1.Describe Rutherford's experiments and atomic model.
Answer:
Rutherford's Experiment:
Rutherford carried outhis experiment by bombarding a very thin gold foil (0.0004 mm) with high speed a particles (He2+) emitted from Radium.
Observations:
1) Majority of a-particles continued their straight path without any deflection.
2) Some particles deflected from their path through large angles.
3) Very few of them returned (1 in 20,000) in opposite direction.
Conclusions:
1) The atom is largely an empty space, since most of a particles pass through the atom.
2) The fact that very few a particles returned in opposite direction, suggests that, whole of positive charge and mass is concentrated at the central point of negligible space called nucleus.
3) The negatively charged electrons remain outside of the nucleus at relatively large distance and are moving in orbits around the nucleus like planet around the sun.
Rutherford's Atomic Model:
1) Nucleus: It is a small positively charged part of the atom. It is situated at the centre andalmost entire mass of the atom. Nucleus contains neutrons and protons.
2) Extra Nuclear Part: This part is empty part of the atom. In this part electrons revolve at very high speed in fixed path, called orbits or shells.
2.What are the drawbacks of Rutherford atomic model?
Answer:
Drawbacks of Rutherford Model:
According to Rutherford's nuclear model of atom, the electrons rotate around the positively charged nucleus in circular orbits- the attractive force of the nucleus
being balanced by the centrifugal force due to rotation of the electrons.
But according to electromagnetic theory, a rotating electron continuously emits radiations and thereby, losses a part of its energy- the equilibrium between the nucleus and electrons is
thus disturbed.
Besides, in the event of rotating electrons continuously, a continuous spectrum is expected to be given by an atom, but a discontinuous line spectrum is actually produced.
3.What are the limitations of Bohr's theory?
Answer:
1) This theory cannot explain the spectrum of atoms or ions containing two or more electrons.
2) This theory failed to explain the splitting of some of the spectral lines into a group of finer lines under the influence of magnetic and electric field.
3) Bohr considered a two dimensional model of the atom, but actually an atom is three dimensional.
4) This is agains Heisenberg's Uncertainty Principle which states that it is impossible to determine simultaneously the exact position and momentum of electron.
4.State Heisenberg's uncertainty principle.
Answer:
Heisenberg's Uncertainty Principle: According to uncertainty principle, "It is impossible to measure simultaneously both the position and momentum (or velocity) of a microscopic particle with absolute accuracy and certainty.
5.What is quantum number?
The numbers used for
completely characterizing each electron of an atom are known as Quantum Numbers. Four such
Quantum numbers are found to be necessary for describing completely an electron. They are-
1) Principal Quantum Number
2 Azimuthal Quantum Number
3) Magnetic Quantum Number
4) Spin Quantum Number
6.Why NaCl is an electrovalent compound?
The compounds which are formed by the transfer of one or more electrons from one atom to
the other atom present in the compound are known as electrovalent compounds. Since NaCl compounds are also formed by the transfer of one electron thus, NaCl is an electrovalent compound.
