Question:
Describe Bohr’s model of the atom.
Answer:
In 1913, Neil Bohr overcame the limitations of Rutherford model and proposed a model model of atomic structure. It has the following postulates:
- Electrons revolve around the nucleus in a limited number of orbits called permissible or discrete orbits.
- These discrete orbits have definite energy hence they are called energy levels or energy shells. These orbits or shells are represented by the letters K,L,M,N,… or the numbers, n=1,2,3,4,…
- The energy of an electron remains constant so long as it stays in the given energy level. It means electrons present in different orbits have different energies.
- When an electron jumps from lower energy level to higher energy level, some energy is absorbed. While some amount of energy is released when an electron jumps from higher energy level to lower one.
Structure of the Atom
Q 1.
What do you think would be the observation if the ?-particle scattering experiment is carried out using a foil of a metal other than gold?
Q 2.
Who discovered protons?
Q 3.
Fill in the blanks :
In the three fundamental sub-atomic particles, _________ are negatively charged, _________ are positively charged and ____________ have no charges.
Q 4.
Describe briefly Thomson's model of an atom.
Q 5.
Write a short note on Nucleus.
Q 6.
Who discovered electrons?
Q 7.
If an atom contains one electron and one proton, will it carry any charge or not?
Q 8.
Fill in the blanks :
Anode rays are also called ___________.
Q 9.
Fill in the blanks :
Rutherford's scattering experiment is related to to the size of ____________.
Q 10.
If A = 23 and Z = 11 for Na atom, how many protons, electrons and neutrons present in Na atom?
Q 11.
Compare an electron, a proton and a neutron in respect of their relative masses and charges.
Q 12.
How many times is a proton heavier than an electron ?
Q 13.
What were the important features of atomic model based on Rutherford's scattering experiment?
Q 14.
What is mass number?
Q 15.
What is the relationship between an atom containing 11 protons, 11 electrons and 11 neutrons, and another atom containing 11 protons, 11 electrons and 12 neutrons ?
Q 16.
What is the maximum number of electrons an M shell of the atom can accommodate ?
Q 17.
State the number of electrons present in the outermost shell of the atoms of the following elements :
(i) Neon(ii)Chlorine
Q 18.
What is ionization energy?
Q 19.
What is the absolute mass and charge of a proton ?
Q 20.
What is the maximum number of electrons which can be accommodated in the L shell of an atom
Q 21.
On the basis of Rutherford’s model of an atom, which subatomic particle is present in the nucleus of an atom?
Q 22.
Give one use each of the following radioactive isotopes :
(a)Uranium-235 (b) Cobalt-60
Q 23.
Fill in the following blanks in respect of an atom of an element :
No.of
protons | No.of
neutrons | Mass number | Atomic
number | No.of
electrons | Valency |
|---|
| 11 | 12 | ........ | ....... | ........ | ......... |
Q 24.
What is a proton ? How does it differ from a neutron ?
Q 25.
Fill in the following blanks
Atomic
number | Mass number | Protons | Neutrons | Electrons | Symbol |
|---|
| 10 | 22 | ....... | ........ | ....... | ........ |
Q 26.
Fill in the blanks :
The maximum number of electrons that can be accommodated in L-shell are _______.
Q 27.
Who discovered nucleus of an atom?
Q 28.
State one use of radioactive isotopes in medicine.
Q 29.
Fill in the following blanks in respect of an atom of an element:
No.of
protons | No.of
neutrons | Mass number | Atomic
number | No.of
electrons | Symbol |
|---|
| 11 | 12 | ........ | ....... | ........ | ......... |
Q 30.
What name is given to those atoms which contain the same number of protons and electrons but different number of neutrons ?
Q 31.
What name is given to the pair of atoms such as
N and
N ?
Q 32.
State the location of electrons, protons and neutrons in an atom.
Q 33.
(a) What are radioactive isotopes ? Give two examples of radioactive isotopes.
(b)Give any two uses of radioactive isotopes.
(c)An element Z contains two naturally occurring isotopes
Z and
Z. If the average atomic mass of this element be 35.5 u, calculate the percentage of two isotopes.
Q 34.
Who discovered neutrons?
Q 35.
Fill in the blanks :
The maximum number of electrons that can be accommodated in K-shell are _______.
Q 36.
What is the absolute mass and charge of an electron ?
Q 37.
How does a proton differ from an electron ?
Q 38.
Name the radioactive isotope which is used in the treatment of cancer.
Q 39.
(a)What are valence electrons ? Where are valence electrons situated in an atom ?
(b)What is the number of valence electrons in the atoms of an element having atomic number 13 ? Name the Valency shell of this atom.
Q 40.
Draw a sketch of Bohr’s model of an atom with three shells.
Q 41.
Fill in the blanks :
Atoms are made up of __________, ___________ and __________.
Q 42.
Fill in the blanks :
_______ are atoms having the same mass number but different atomic numbers.
Q 43.
What is the maximum number of electrons which can be accommodated in the K shell of an atom
Q 44.
What is the electronic configuration of a hydrogen atom
Q 45.
State whether the following statement is true or false :
Radioactive isotope of iodine is used for making the medicine called tincture iodine.
Q 46.
Complete the following statements :
(a) Magnesium has 2 valence electrons in the......... shell.
(b)The valency of nitrogen in N2 molecule is........
(c)Isotopes have different mass numbers because their nuclei contain different number of........
(d) Some boron atoms have mass number 10 and some have mass number 11. These boron atoms with different mass numbers are called............
Q 47.
What is the mass of proton as compared to electron?
Q 48.
What are ?-particles?
Q 49.
Who is known as 'Father of Nucleus Physics'?
Q 50.
What were the observations of Rutherford's ?-scattering experiment?
