Chemistry by Inam Jazbi: IX Chemistry Model Test Questions Chemistry Test # 6 for Chapter # 2 (Atomic Structure)

Model Test Questions Chemistry Test # 6 for Chapter # 2 (Atomic Structure)

Short Questions Answers

Q1. What are Limitations of Bohr's Atomic Model?

Q2. Differentiate between shell and sub shell with examples?

Q3.What is maximum number of electrons that can be accommodate in's' subshell?

Q4. How many electrons will be in L shell of an atom having atomic number 11?

Q5. In the distribution of electrons of an atom, which shell filled first and why?

Q6. If both K and L shells of an atom are completely filled, what is the total number of electrons are present in them?

Q7. An atom has 5 electrons in M shell than:

(a) Find out its atomic number?

(b) Write Electronic configuration of atom?

Q8. Describe wave particle duality of electron of De Broglie Hypothesis?

Long Questions Answers

Q9. Prove that modern theory of De Broglie is related with Einstein and Plank's equations.

Q10. Describe the schrodinger atomic model.

Q11.Explain how Bohr's atomic model is different from Rutherford atomic model.

State postulates of Bohr’s atomic model.

Q12. Write down electronic configuration of B, F, N, Na, P, Cl, Ca, K⁺, O^2-, S^2-, Mg²⁺, Cl^-.

جو ہم نہ ہوں تو زمانے کی سانس رک جائے

قتیلؔ وقت کے سینے میں ہم دھڑکتے ہیں

Solutions of Questions

Q1. What are Limitations of Bohr's Atomic Model?

Answer

1. It failed to explain the Zeeman Effect (effect of magnetic field on the spectra of atoms).

2. It also failed to explain the Stark effect (effect of electric field on the spectra of atoms).

3. It is against the Heisenberg Uncertainty Principle.

4. It could not explain the spectra obtained from larger atoms.

5. It explained the mono-electronic species like H⁺, Li²⁺, B³⁺.

Q2. Differentiate between shell and sub shell with examples?

Q8. Describe wave particle duality of electron of De Broglie Hypothesis?

Answer

In 1923 Lois De Broglie extend the wave particle duality to electron, and propose a hypothesis that all matter has particle as well as wave nature at the submicroscopic level.

De Broglie combined the Einstein and Planck equations to derive its de-Broglei’ equation. The wave nature of a particle is quantified by De Broglie wavelength defined as l = h/p where p is the momentum of the particle.

All matter (material) particles in motion have a dual character exhibiting both particle and wave nature i.e. electrons, protons, neutrons, atoms, and molecules possess the characteristics of both the material particle and a wave. This is called wave-particle Duality in matter.

de-Broglie derived a mathematical equation known as de-Broglie’s equation which relates the wavelength (l) of the material particle (electron) of mass m moving with velocity v to its momentum (mv = p):

Q9. Prove that modern theory of De Broglie is related with Einstein and Plank's equations.

Answer

Q10. Describe the schrodinger atomic model.

Answer

In 1926 Erwin Schrödinger, an Austrian physicist, took the Bohr’s atomic model one step forward. Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position. This atomic model is known as the quantum mechanical model of the atom.

The quantum mechanical model determines that electron can be find in various location around the nucleus. He found electrons are in orbit as an electron cloud.

Basic Postulates

1. The quantum mechanical model determines that electron can be found in various location around the nucleus as an electron cloud (Electrons in orbits are found as an electron cloud).

2. Each energy subshell in an orbit has different shapes which determine the presence of electron.

3. Different subshells or orbitals are named as s, p, d and f with different shapes. e.g. s-orbital is spherical and p-orbital is dumbbell shaped.

4. The numbers and kind of atomic orbitals depends on the energy subshell.

According to quantum mechanical model probability of finding an electron within certain volume of space surrounding the nucleus can be represented as a fuzzy cloud. The cloud is denser the probability of finding

electron is high which are called atomic orbitals.

Q11. Explain how Bohr's atomic model is different from Rutherford atomic model.

State postulates of Bohr’s atomic model.

Answer

Introduction

After Planck and Einstein’s discoveries, a Danish Physicist Neil Bohr in 1913 offered a theoretical explanation of line spectra of hydrogen atom and proposed a new model for structure of atom based on Planck’s Quantum theory of Max Planck.

Basic Postulates

Postulate # 1

The atom has a number of fixed energy orbits or energy levels called stationary orbit’s or permissible orbits in which electron revolves around the nucleus. Bohr adopted Planck’s idea that energies are quantized. These orbits or shells have certain fixed amount of energy and are named as K, L, M, N. Electrons in atoms move only in certain allowed energy levels in which they are completely stable and will not emit or absorb energy continuously and therefore will not spiral (fall) into the nucleus.

Postulate # 2

When an electron jumps from lower energy level (E₁) to higher energy level (E₂), it absorbs a definite discrete quantity of energy called quantum of energy. When electron jumps from higher energy level (E₂) to lower energy level (E₁), it emits energy (as a light in a definite discrete quantity called quantum of energy). A quantum of energy is directly proportional to the frequency of the radiation. Since the process of emission of energy is not continuous, so a line spectrum is produced by atoms.

Postulate # 3

an electron cannot revolve in an arbitrary orbits but only those orbits are permissible (which are called allowed orbits or stationary states) in which angular momentum of electrons is an integral (whole number) multiple of h/2p.

mvr = nh/2p.

[Where; n = Principal quantum number = number of orbits = 1, 2, 3 …., h = Planck’s constant]