Collisions of electrons with atoms Flashcards
What is an ion?
an ion is a charged atom
the number of electrons in an ion is not equal to the number of protons
What is ionisation?
How does it occur?
the adding or removing of ions
alpha, beta and gamma radiation create ions when they pass through substances and collide with atoms
electrons passing through a fluorescent tube create ions when they collide with atoms of the gas or vapour in the tube
What is an electron volt?
unit equal to the work done when an electron is moved through a pd of 1v
work done = q V
therefore the work done when an electron moves through a pd of 1V is equal to 1.6x10^-19J
What is the process of excitation?
using gas-filled tubes with a metal grid between the filament and the anode
we can show gas atoms can absorb energy from colliding electrons without being ionised
When does excitation occur?
happens at certain energies, which are characteristic of the atoms of the gas
How does KE effect current and excitation?
if the electron loses all its KE after it causes excitation, the current due to the flow of electrons is reduced
if the electron does not have enough KE to cause excitation, it will deflect off the atom with no overall loss of KE
What are excitation energies? How is it measured?
the energy values at which an atom absorbs energy
in a gas-filled tube, increasing the pd between the filament and the anode and measuring the pd when the anode current falls
What happens in terms of energy levels happens to the electron? Why is excitation energy lower than ionisation energy?
the collding electron makes an electron inside the atom move from an inner shell to an outer shell
energy is needed for this process to make the atomic electron move away from the nucleus
excitation energy is always less than the ionisation energy of the atom, because the electron is not completely removed
