Structure Of Atoms

Question 1

How was the discovery of electrons different from that of the proton?

Answer 1

The discovery of electrons involved in a discharged tube with very low temperature and high voltage. Making the rays invisible to the naked eye

the discovery of protons involved in the same discharge with a decrease in pressure. The rays made were visible to the naked eye in the form of light rays.

Question 2

What were the conclusions drawn from the cathode and anode ray discharged tube experiments?

Answer 2

For the cathode ray discharge tube experiment,
1. the particles were negatively charged
2. they possess mechanical energy
3. moving from cathode to anode
4. they deviate in the presence of electrical and magnetical field
5. they don’t depend on the nature of gas

For the Anode ray discharged tube,
1. they depend on the nature of the gas
2. positively charged particles
3. they act oppositely in the presence of electrical and mechanical fields.
4. The moved from the anode to cathode

Question 3

Why do you think the idea of neutron came into play?

Answer 3

The existence of mass that is more than predicted gave rise to a new subatomic particle called the neutron. Having zero charge and mass almost equivalent to that of the proton

Question 4

Give the values of the following constants
1. charge to mass ratio
2. mass of electron
3. charge of electron
4. Mass of proton
5. Mass of neutron
6. charge of proton

Answer 4

the values are as follows
1. 1.7 * 10^11C/kg
2. 9.1 * 10^-31 kg
3. -1.6 * 10^-19 C
4. 1.62 * 10^-27 kg
5. 1.64 * 10^-27 kg
6. +1.6 * 10^-19 C

Question 5

Describe the plum pudding model given by J.J Thomson.

Answer 5

Description: the model given by J.J. Thomson was structured as follows, he assumed the atom to be a sphere where the mass is distributed evenly and negative charges were embedded in it

names: plum pudding, raisin pudding, watermelon

Drawbacks:
1.didn’t explain the later on experiments carried out

Question 6

What was the basic idea of Rutherford’s atomic model?

Answer 6

The basic idea behind his model was that after the conduction of the alpha particle scattering experiment, he concluded that
1. mass is concentrated at a point called the nucleus
2. electrons revolve around the nucleus in fixed paths
3. more than half of the space in the atom is empty

name: solar system

Question 7

What were the points that Bhor’s model explained that Rutherford missed?

Answer 7

The points Bhor’s model could explain were
1. the stability of the atom
2. the energy of the orbits
3. The distribution of electrons

Question 8

With the help of which theories was Bhor able to explain the drawbacks of Rutherford’s model?

Answer 8

The concepts of
1. particle behavior of waves
a. photoelectric effect
b. black body radiation
2. atomic spectrum

Question 9

Define these terms
1. Wavelength
2. Frequency
3. Wave number
4. Amplitude

Answer 9

The terms are defined as follows
1. Wavelength is defined as the length of one cycle i.e. one trough and one crest
2. Frequency is defined as the number of waves passing per second from a fixed point
3. Wave number as defined as the inverse of wavelength
4. Amplitude is defined as the maximum height the wave can rise up to.

Question 10

What is an electromagnetic wave?

Answer 10

An electromagnetic wave can be defined as a wave that propagates when a particle with alternating magnetic and electrical fields moves and accelerates.

Properties:
1. they don’t need a defined medium
2. the direction of propagation, electrical and magnetical fields are all perpendicular to each other
3. this can break into a spectrum
gamma rays, X-rays, UV rays, Visible spectrum(400 nm to 750nm) , IR , Microwaves, Radio waves
4. In a vacuum travels at the speed of light, all the rays
c = λv

Question 11

What is the phenomena of black body radiation?

Answer 11

Black body radiation is where when a perfect absorber or radiator (black body) radiates energy is called black body radiation.

Question 12

What is photoelectric effect

Answer 12

The photoelectric effect is where when a particle of light falls on a metal surface there is a transfer of energy. If the transfer is larger than the work function the particle will be ejected out with a certain energy which is used as its k.E.

hv = Wo + 1/2 mv^2
Wo =hvo

Vo = threshold frequency: the minimum frequency needed for ejection of electron

Question 13

What is the energy theory given by Plank?

Answer 13

The theory states that energy is absorbed or radiated in discreate amounts .
E = hv
h=6.626 * 10^-34 Js

Question 14

Atomic spectrum

Answer 14

Atomic spectrum : when the electron absorb or radiate a certain frequency gives out a spectrum

a)Absorption : where the electron absorbs a frequency and travel to higher orbitals. Make the atom unstable

b) Emission : where electrons return to its ground state by radiating energy. Making the atom stable

Question 15

Atomic spectrum for hydrogen

Answer 15

The spectrum for hydrogen depending on the shell number was discovered by different scientist.

1. Layman - shell 1 UV rays
2. Balmar - shell 2 Visible spectrum
3. Paschen - shell 3 IR
4. Bracket - shell 4
5. Pfund - shell 5

wave number = 109776[1/n1^2 -1/n2^2]

Question 16

Bhor’s Atomic model

Answer 16

1. Their are defined orbitals with defined energy levels
2. after reaching the ground state the electron can’t lose anymore energy
3. the radius of the orbital is defined as
   r = a* n^2/z
4. Angular momentum is integral multiple of h/2π
   mvr = n(h/2π)
5. E = - 2.18 *10^-18 [1/n^2]
   energy is equal to zero when the electron reaches infinity
6. v = Δ E/h =3.29 * 10^15 [1/ni -1/nf]

Question 17

What was the reason/s for the rise of a new atomic model after bhor’s model ?

Answer 17

The reason that there was a need for a new model was,
1. it didn’t apply on all atoms
2. it could not explain the effect of electrical and magnetical fields on the atomic spectra

Question 18

Define these concepts
1.De Broglie’s equation
2. Heisenberg’s uncertainty principle

Answer 18

1. De Broglie’s equation: all particles having charge have duel behavior.
   λ = h/mv p = mv
2. Heisenberg’s uncertainty principle: the position of an electron and its velocity can’t be defined at the same time
   Δx.Δv >= h/4πm

Question 19

Define the quantum model of atom

Answer 19

This model is defined on the bases of Schrodinger’s equation ,De Broglie’s equation and Heisenberg’s uncertainty principle.

The main features are:
1. that energy is quantized
2. the information of the location of electron is given by Schrodinger’s equation , and Heisenberg’s uncertainty principle
3. this quantized energy depends on the wave nature of the particle

Question 20

What was the main concept given by the quantum model?

Answer 20

The main concept give is that of the quantum numbers:
1. Principle quantum number: it tells us about the shell the electron is located in and the energy level of the shell
2. Azimuthal quantum number: lets us about the shape of the orbital
s - 0(1) p - 1(3) d - 2(5) f - 3(7)
l = 0, 1, …….. (n-1)
4. Magnetic quantum number: it tells us about the orientation of the orbital
m = -l,……..,l
5. Spin quantum number: It lets us about the direction of spin of the electron
+1/2 and -1/2

Question 21

What are nodes?

Answer 21

Nodes are the region where there is zero possibility of finding electrons.

for a normal node the formula is (n-l) where l is the specific orbital

for a radical node (n-1-l)

Question 22

What are rules for filling electrons in shells?

Answer 22

The rules that are followed for filling electron are:
1. Aufbau’s principle: electrons are to be filled in the increasing order of energy
2. Pallia’s exclusion principle: two electron in the same orbital should not have the same set of 4 quantum numbers
3. Hund’s rule: electron are initially singly filled in the orbitals and then paired up.

Question 23

Why are half filled orbitals more stable that fully filled orbitals?

Answer 23

The reason for more stability in half filled electrons are:
1. then their is symmetry
2. higher exchange of energy brings more stability

Question 24

Define these terms
1. degenerating orbitals
2. ground state
3. excited state
4. shelfing effect
5. Effective nuclear charge

Answer 24

These terms are defined as
1. degenerating orbitals: orbitals have the same energy levels
2. ground state: lowest energy level
3. excited state: highest energy level
4. shelfing effect : the repulsion experienced by the outer electron due to the inner electrons
5. Effective nuclear charge: the decrease in the positive charge effect on the outer most electron