3.3 Collisions of Electrons with Atoms Flashcards
What is an ion
A charged atom
What is special about ions
The number of electrons is not equal to the number of protons
How is an ion formed
When adding or removing electrons from an uncharged atom
What happens if electrons are added to an atom
It becomes a negative ion
Any process of creating ions is called ______.
Ionisation
Alpha, beta and gamma radiation create ions when they pass through ______ and ______ with the atoms of the substance.
Substances
Collide
Electrons passing through a ______ tube create ions when they ______ with the atoms of the gas or vapour in the tube.
Fluorescent
Collide
How can we measure the energy needed to ionise a gas atom
By making electrons collide at increasing speed with the gas atoms in a sealed tube
The electrons are emitted from heated filament in tube and are attracted to a positive metal plate (anode) at other end of tube
What conditions are necessary to measure the energy needed to ionise a gas atom
Gas must be at a sufficiently low pressure otherwise there are too many atoms in tube and electrons cannot reach the anode
Potential difference between anode and filament is increased to increase speed of electrons
Ionisation near anode causes much greater current to pass through ammeter
By measuring pd when current starts to increase, we can calculate ionisation energy of gas atom as this is equal to work done on each electron from filament
The work done on each electron from the filament is given by its…
charge e * the tube potential difference V
The ionisation energy of a gas atom =
eV
What is the electron volt
A unit of energy equal to the work done when an electron is moved through a pd of 1V
For a charge q moved through a pd V, the work done =
qV
The work done when an electron moved through a potential difference of 1V is equal to…
1.6*10^-19 J
This amount of energy is defined as 1 eV (electron volt)
The work done on an electron when it moves through a potential difference of 1000V is…
1000eV
The work done on an ion of charge +2e when it moves through a potential difference of 10V is…
20eV
What is the process of excitation
The process of gas atoms being able to absorb energy from colliding electrons without being ionised
Happens at certain energies which are characteristic of the atoms of the gas
If a ______ electron does not have enough kinetic energy to cause ______, it is deflected by the ______, with no overall loss of kinetic energy.
Colliding
Excitation
Atom
What are an atom’s excitation energies
The energy values at which an atom absorbs energy
How can we determine the excitation energies of atoms in a gas-filled tube
By increasing the potential difference between the filament and the anode and measuring the pd when the anode current falls
When excitation occurs, the ______ ______ makes an electron inside the atom ______ ______ from the nucleus of the atom. The excitation energy is always ______ than the ______ energy of the atom as the atomic electron is not removed completely from the atom when excitation occurs.
Colliding electron
Move away
Less
Ionisation
