Important Short Questions of 9th Chemistry CHAPTER No 2

Write down two observations of Rutherford’s Atomic model.

  1. Most of the alpha particles passed through the foil un-deflected.
  2. Out of 20000 particles only a few were deflected at fairly large angles and very few bounced back on hitting the gold foil.

Where does the most of mass of an atom exist?

Most of an atom exists in its nucleus.  Protons and neutrons are present in nucleus.  The sum of masses of protons and neutrons is equal to atomic mass of an atom.

Write down two postulates of Rutherford’s atomic model.

  1. The hydrogen atom consists of a tiny nucleus and electrons are revolving in one of the circular orbits of radius ‘r’ around the nucleus.
  2. Each orbit has a fixed energy that is quantized.

Describe difference between Rutherford’s atomic theory and Bohr’s atomic theory.

Rutherford’s Atomic theory:

It was based on classical theory.

Electrons revolve around the nucleus

No idea about the orbit was introduced

Atoms should produce continuous spectrum

Atoms should collapse

Bohr’s atomic theory

It was based upon quantum theory

Electrons revolve around the nucleus in orbits of fixed energy

Orbits had quantized angular momentum

Atoms should produce line spectrum

Atoms should collapse

When does an electron emit or absorb energy?

  1. According to Bohr when electron jumps from higher to lower energy orbit it radiates energy
  2. Similarly when electron jumps from lower energy orbit to higher energy orbit it absorbs energy

What is meant by quantum? Or why Max Plank was awarded Noble prize? Or what is meant by quantum and quanta?

Quantum means fixed energy.  It is smallest amount of energy that can be emitted or absorbed as electromagnetic radiations. Quanta is plural of quantum.  In 1918, Noble prize in physics was awarded to German physicist Max Plank for work on quantum theory.

Calculate the value of angular momentum of 1st orbit where mvr=nh/2pi

Let angular momentum of first orbit is mvr=nh/2pi

               By putiing the values of h and , mvr= (1)(6.63*10^-34)/2*3.14


Define electronic configuration.

The distribution of electrons around the nucleus in various shells and sub shells according to their increasing energy is called electronic configuration.

An element has 5 electrons in M shell.  Find its atomic number.

The elements has five electrons in M shell has atomic number 15 and the name of element is phosphorus.

Write down the number and names of subshells in N shell.

Number of sub shell in N shell is 4 named as s, p, d and f.

How many electrons can be present in K, L, M and N shell?

What is maximum capacity of metal? Or how many electrons can be accommodated in different shells of an atom?

K shell can accommodate 2 electrons.

L shell can accommodate 8 electrons

M shell can accommodate 18 electrons

N shell can accommodate 32 electrons.

Write down the defects of Rutherford’s atomic model.

  1. According to the classical theory electron being charged particle should release or emit energy continuously and they should ultimately fall into the nucleus.
  2. If the electron emits energy continuously they should form a continuous spectrum but in fact line spectrum was observed.

Electronic Configuration of 30 elements

Atomic NumberName of the ElementElectronic Configuration
1Hydrogen (H)1s1
2Helium (He)1s2
3Lithium (Li)[He] 2s1
4Beryllium (Be)[He] 2s2
5Boron (B)[He] 2s2 2p1
6Carbon (C)[He] 2s2 2p2
7Nitrogen (N)[He] 2s2 2p3
8Oxygen (O)[He] 2s2 2p4
9Fluorine (F)[He] 2s2 2p5
10Neon (Ne)[He] 2s2 2p6
11Sodium (Na)[Ne] 3s1
12Magnesium (Mg)[Ne] 3s2
13Aluminium (Al)[Ne] 3s2 3p1
14Silicon (Si)[Ne] 3s2 3p2
15Phosphorus (P)[Ne] 3s2 3p3
16Sulphur (S)[Ne] 3s2 3p4
17Chlorine (Cl)[Ne] 3s2 3p5
18Argon (Ar)[Ne] 3s2 3p6
19Potassium (K)[Ar] 4s1
20Calcium (Ca)[Ar] 4s2
21Scandium (Sc)[Ar] 3d1 4s2
22Titanium (Ti)[Ar] 3d2 4s2
23Vanadium (V)[Ar] 3d3 4s2
24Chromium (Cr)[Ar] 3d5 4s1
25Manganese (Mn)[Ar] 3d5 4s2
26Iron (Fe)[Ar] 3d6 4s2
27Cobalt (Co)[Ar] 3d7 4s2
28Nickel (Ni)[Ar] 3d8 4s2
29Copper (Cu)[Ar] 3d10 4s1
30Zinc (Zn)[Ar] 3d10 4s2

Structure of Atom

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