3.3 Collisions Of Electrons With Atoms *Diagrams Flashcards
What is an ion
A charged atom
How is an ion formed
By adding or removing electrons from an uncharged atom
What does adding electrons to an atom make
A negative ion
What does removing electrons from an atom make
A positive ion
What is the process of creating ions called
Ionisation
What do alpha beta and gamma radiation create when they passed through substances and collide with the atoms of the substance
Ions
What do electrons passing through a fluorescent tube create when they collide with the atoms of gas or vapour in the tube
Ions
What is the electron volt
Are units of energy equal to the work done when an electron is move through a potential difference of one volt
What is the potential difference of 1 V
1.6x10^-19
How can we show that gas atoms can absorb energy from colliding electrons without being ionised
Using gasfield tubes with a metal grid between the filament on the anode
What is excitation
When gas atoms can absorb energy from colliding electrons without being ionise
When does excitation happen
At certain energy which are characteristics of the atoms of the gas
What happens if a colliding electron loses all its kinetic energy when it causes excitation
The current due to the flow of electrons through the gas is reduced.
What happens if the colliding electron does not have enough kinetic energy to cause excitation
It is deflected by the atom with no overall loss of kinetic energy
What are excitation energies
The energy values of which an atom absorbs energy
How can we determine excitation energies of atoms
In gas filled tube
by increasing the potential difference between the filament in the anode and measuring the potential difference when the anode current falls
What happens to the electrons in excitation
The colliding electron makes an electron inside the atom move up from an inner to an outer shell
Why is energy needed for excitation
Because the atomic electron moves away from the nucleus of the atom
Why is excitation energy always less than ionisation energy
Because the atomic electron is not removed completely from the atom when excitation occurs
Why does the gas need to be at a sufficiently low pressure when measuring ionisation energy
Otherwise there will be too many atoms in the tube and the electrons can’t reach the anode
What happens to the pd when measuring ionisation energy
The pd between the anode and the filament is increased so as to increase the speed of electrons
Why does the ammeter record a very small current
Due to electrons from the filament reaching the anode
What does no ionisation occur until
Electrons from the filament reach a certain speed
At this speed each electron arrives near the anode with just enough kinetic energy to ionise a gas atom by knocking an electron out of the atom
What does ionisation near the anode cause
A much greater current to pass through the ammeter
How can we calculate the ionisation energy of a gas atom
By measuring the pd (V) between the filament and the anode when the current starts to increase
Ionisation energy of gas is equal to work done (W) on each election form the filament (and work done is transformed into kinetic energy)
Work done on each electron = charge of electron x tube of potential difference
