Explaining The Evidence: The Bohr Theory

Question 1

What did Bohr’s theory introduce the idea of?

Answer 1

The idea of quantisation of energy, i.e. that an electron in an atom can only have a fixed amount of energy

Question 2

What is a quantum of energy?

Answer 2

The fixed amount of energy that in an electron in an atom can have

Question 3

What does quantisation mean?

Answer 3

This means that the energy of an electron in an atom cannot have just any value but may only have certain specific values

Question 4

What is Bohr’s theory often described as providing?

Answer 4

As providing spectroscopic evidence for the existence of energy levels.

Question 5

What did Bohr suggest in relation to the movement of electrons?

Answer 5

Electrons revolve around the nucleus in fixed paths called orbits

Question 6

What are orbits also called?

Answer 6

Energy levels

Question 7

Describe the energy that electrons have in an orbit.

Answer 7

Electrons in any one orbit have a fixed amount of energy

Question 8

What are energy levels represented by?

Answer 8

They are represented by the letter n

Question 9

What is the lowest energy level represented by?

Answer 9

n=1

Question 10

What is the next energy above from n=1 represented by?

Answer 10

n=2

Question 11

Describe the energy of the electron in a particular energy level.
(2)

Answer 11

The energy in a particular orbit or energy level is quantised, i.e. fixed at a definite value

An electron will have a certain amount of energy depending on the orbit or energy level in which it is located

Question 12

Define an energy level.

Answer 12

An energy level is defined as the fixed energy value that an electron in an atom may have

Question 13

How did Bohr explain why electrons do not lose energy and fall into the nucleus?

Answer 13

He stated that as long as an electron is in any one particular energy level, it neither gains nor loses energy

Question 14

Under what condition will an electron neither gain nor lose energy?

Answer 14

As long as an electron is in any one particular energy level

Question 15

At what state do atoms normally exist?

Answer 15

They normally exist in the ground state

Question 16

Define the ground state.

Answer 16

The ground state of an atom is one in which the electrons occupy the lowest available energy levels

Question 17

Describe the energy an electron has when the atom in the ground state.

Answer 17

Electrons in the ground state have energy of fixed values, i.e. the energy of the electrons in a particular orbit or energy level is fixed or quantised

Question 18

Describe the energy electrons occupy in the ground state.

Answer 18

In the ground state the electrons occupy the lowest available energy levels

Question 19

What happens when an atom in the ground state is provided with energy?

Answer 19

A specific amount of this energy is absorbed and the electrons jump from lower energy levels to higher energy levels - electrons are now in the excited state

Question 20

Define the excited state.

Answer 20

The excited state of an atom is one in which the electrons occupy higher energy levels than those available in the ground state

Question 21

How does an atom enter the excited state?

Answer 21

When an atom in the ground state is provided with energy

Question 22

Describe the absorbed energy when an electron becomes excited.

Answer 22

The energy absorbed is equal to the difference in energy between the ground state/lower energy level and an excited state/a higher energy level

Question 23

Describe the electrons in the excited state?

Answer 23

They are unstable and they fall back down to lower energy levels after a short period of time

Question 24

What happens as an electron falls back to a lower energy level from its excited state?

Answer 24

Energy is released in the form of a photon of light which has a definite amount of energy i.e. light of a definite frequency is given off

Question 25

What does the frequency of the light emitted depend on?

Answer 25

The difference in energy between the two energy levels

Question 26

Give the equation for the frequency of light.

Answer 26

E2 - E1 = hf

Question 27

What does h = in the following equation? | E2 - E1 = hf

Answer 27

Planck's constant

Question 28

What does f = in the following equation? | E2 - E1 = hf

Answer 28

Frequency of light emitted

Question 29

What does E2 = in the following equation? | E2 - E1 = hf

Answer 29

Energy of higher energy level

Question 30

What does E1 = in the following equation? | E2 - E1 = hf

Answer 30

Energy of lower energy level

Question 31

What does E2 - E1 = hf tell us?

Answer 31

It tells us that the energy difference is proportional to the frequency of the light emitted

Question 32

What does the definite amount of energy emitted appear as?

Answer 32

It appears as a line of a particular colour

Question 33

When a definite amount of energy is emitted when an electron falls from one energy level to another it appears as a line of a particular colour, what does this form?

Answer 33

This forms an emission line spectrum

Question 34

What piece of evidence implies that electrons can occupy only definite energy levels?

Answer 34

Since only definite amounts of energy are emitted

Question 35

Only definite amounts of energy are emitted when an electron falls from its excited state to its ground state, what does this indicate?

Answer 35

this implies that definite amounts of energy are emitted

Question 36

Each definite amount of energy emitted gives rise to what?

Answer 36

A line in the emission spectrum

Question 37

Summarise Bohr's Theory (the general points only) | 5

Answer 37

Electrons revolve around the nucleus in fixed paths called orbits Electrons in any one orbit have a fixed amount of energy Energy levels are represented by the letter n The energy of the electron in a particular orbit or energy is quantised As long as an electron is in any one particular energy level, it neither gains nor loses energy

Question 38

Summarise Bohr's Theory (the points on the ground state) | 4

Answer 38

Atoms normally exist in the ground state Electrons in the ground state have energy of fixed values In the ground state the electrons occupy the lowest available energy levels When an atom in its ground state is provided with energy a specific amount of this energy is absorbed and the electrons jump from lower energy levels to higher energy levels - excited state

Question 39

Summarise Bohr's Theory (the points on the excited state) | 4

Answer 39

The energy absorbed is equal to the difference in energy between the lower energy level and a higher energy level Electrons in the excited state are unstable and they fall back down to lower energy levels after a short period of time As an electron falls back to a lower energy level, the excess energy is released in the form of a photon of light which has a definite amount of energy The frequency of the light emitted depends on the difference in energy between the two energy levels

Question 40

Summarise Bohr's Theory (the points on the line spectra) | 5

Answer 40

The energy difference is proportional to the frequency of the light emitted The definite amount of energy emitted appears as a line of particular colour Since only definite amounts of energy are emitted, this implies that electrons can occupy only definite energy levels Each definite amount of energy emitted gives rise to a line in the emission spectrum Each element has a unique emission line spectrum

Question 41

What are the names of the two invisible series of transitions?

Answer 41

Paschen series Lyman series

Question 42

What is the name of the visible series of transitions?

Answer 42

Balmer series

Question 43

What transitions are involved in the Paschen series?

Answer 43

All transitions between that fall to n=3 E,g. 5 to 3, 4 to 3, or higher 6 to 3, 7 to 3

Question 44

What transitions are involved in the Lyman series

Answer 44

All transitions that fall to n=1 e.g. n=5 to n=1, n=3 to n=1 etc

Question 45

What transitions are involved in the Balmer series?

Answer 45

All transitions that fall to n=2 e.g. n=3 to n=2 or n=5 to n=2

Question 46

Where is the Paschen series found?

Answer 46

It is found in infrared region

Question 47

Where is the Lyman series found?

Answer 47

In the ultraviolet region

Question 48

Which series is found in the infrared region?

Answer 48

Paschen series

Question 49

Which series is found in the Lyman series?

Answer 49

Lyman series

Question 50

What series are the transitions to n=3 called?

Answer 50

Paschen series/ infrared series

Question 51

What series are the transitions to n=2 called?

Answer 51

Balmer series

Question 52

What series are the transitions to n= 1 called?

Answer 52

Lyman series