Explaining The Evidence: The Bohr Theory Flashcards
What did Bohr’s theory introduce the idea of?
The idea of quantisation of energy, i.e. that an electron in an atom can only have a fixed amount of energy
What is a quantum of energy?
The fixed amount of energy that in an electron in an atom can have
What does quantisation mean?
This means that the energy of an electron in an atom cannot have just any value but may only have certain specific values
What is Bohr’s theory often described as providing?
As providing spectroscopic evidence for the existence of energy levels.
What did Bohr suggest in relation to the movement of electrons?
Electrons revolve around the nucleus in fixed paths called orbits
What are orbits also called?
Energy levels
Describe the energy that electrons have in an orbit.
Electrons in any one orbit have a fixed amount of energy
What are energy levels represented by?
They are represented by the letter n
What is the lowest energy level represented by?
n=1
What is the next energy above from n=1 represented by?
n=2
Describe the energy of the electron in a particular energy level.
(2)
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
Define an energy level.
An energy level is defined as the fixed energy value that an electron in an atom may have
How did Bohr explain why electrons do not lose energy and fall into the nucleus?
He stated that as long as an electron is in any one particular energy level, it neither gains nor loses energy
Under what condition will an electron neither gain nor lose energy?
As long as an electron is in any one particular energy level
At what state do atoms normally exist?
They normally exist in the ground state
Define the ground state.
The ground state of an atom is one in which the electrons occupy the lowest available energy levels
Describe the energy an electron has when the atom in the ground state.
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
Describe the energy electrons occupy in the ground state.
In the ground state the electrons occupy the lowest available energy levels
What happens when an atom in the 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 - electrons are now in the excited state
Define the excited state.
The excited state of an atom is one in which the electrons occupy higher energy levels than those available in the ground state
How does an atom enter the excited state?
When an atom in the ground state is provided with energy
Describe the absorbed energy when an electron becomes excited.
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
Describe the electrons in the excited state?
They are unstable and they fall back down to lower energy levels after a short period of time
What happens as an electron falls back to a lower energy level from its excited state?
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
What does the frequency of the light emitted depend on?
The difference in energy between the two energy levels
Give the equation for the frequency of light.
E2 - E1 = hf
What does h = in the following equation?
E2 - E1 = hf
Planck’s constant
What does f = in the following equation?
E2 - E1 = hf
Frequency of light emitted
What does E2 = in the following equation?
E2 - E1 = hf
Energy of higher energy level
What does E1 = in the following equation?
E2 - E1 = hf
Energy of lower energy level
What does E2 - E1 = hf tell us?
It tells us that the energy difference is proportional to the frequency of the light emitted
What does the definite amount of energy emitted appear as?
It appears as a line of a particular colour
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?
This forms an emission line spectrum
What piece of evidence implies that electrons can occupy only definite energy levels?
Since only definite amounts of energy are emitted
Only definite amounts of energy are emitted when an electron falls from its excited state to its ground state, what does this indicate?
this implies that definite amounts of energy are emitted
Each definite amount of energy emitted gives rise to what?
A line in the emission spectrum
Summarise Bohr’s Theory (the general points only)
5
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
Summarise Bohr’s Theory (the points on the ground state)
4
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
Summarise Bohr’s Theory (the points on the excited state)
4
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
Summarise Bohr’s Theory (the points on the line spectra)
5
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
What are the names of the two invisible series of transitions?
Paschen series
Lyman series
What is the name of the visible series of transitions?
Balmer series
What transitions are involved in the Paschen series?
All transitions between that fall to n=3
E,g. 5 to 3, 4 to 3, or higher 6 to 3, 7 to 3
What transitions are involved in the Lyman series
All transitions that fall to n=1
e.g. n=5 to n=1, n=3 to n=1 etc
What transitions are involved in the Balmer series?
All transitions that fall to n=2
e.g. n=3 to n=2 or n=5 to n=2
Where is the Paschen series found?
It is found in infrared region
Where is the Lyman series found?
In the ultraviolet region
Which series is found in the infrared region?
Paschen series
Which series is found in the Lyman series?
Lyman series
What series are the transitions to n=3 called?
Paschen series/ infrared series
What series are the transitions to n=2 called?
Balmer series
What series are the transitions to n= 1 called?
Lyman series
