physics chapter 3.4-3.6 quantum phenomena

what are electrons in an atom trapped by

the electrostatic force of attraction of the nucleus

what electron shell has the most energy

the shell furthest away from the nucleus

ground state

the lowest energy state of an atom

when is an atom in an excited state

when an atom in the ground state absorbs energy, and one of its electrons moves to a shell at higher energy

why is the electron configuration in an excited atom unstable

because an electron that moves to an outer shell leaves a vacancy in the shell it moves from

the process of de-excitation

when a vacancy, due to an electron having moved to an outer shell in an excited atom, is filled by an electron from an outer shell transferring to it, the electron emits a photon

what is the energy of a photon emitted when an atom de-excited equal to

the energy lost by the electron and so the atom

equation for the energy of an emitted photon

hf = energy level 1 (E1) - energy level 2 (E2)

why do certain substances fluoresce/glow with visible light when they absorb UV radiation

atoms in the substance absorb UV photons and become excited, + when the atoms de-excite they emit visible photons - when the source of UV radiation is removed, the substance stops glowing

why do fluorescent colours glow

ionisation + excitation occurs as atoms collide with each other + electrons; atoms emit UV photons, along with visible photons, when they de-excite; UV photons are absorbed by the atoms of the fluorescent coating, causing excitation of atoms; coating atoms de-excite in steps + emit visible photons

what are the wavelengths of the lines of a line spectrum of an element characterised by

the atoms of that element - so by measuring the wavelength of a line spectrum, we can identify the element that produced the ligth

equation for the energy of an emitted photon

hf = energy level 1 (E1) - energy level 2 (E2)

photons

particle-like packeys of electromagnetic waves

when is the wave-like nature of light observed

when diffraction of light takes place e.g. when light passes through a narrow slit

how is the wave like nature of light shown when light passes through a narrow slit

the light emerging from the slit spreads out in the same way as water waves spread out after passing through a gap - the narrower the gap or longer the wavelength, the greater the amount of diffraction

when is the particle-like nature of light observed

in the photoelectric effect for example - when light is directed at a metal surface + an electron at the surface absorbs a photon of frequency f, the kinetic energy of the electron is increased from a negligible value by hf

when can electron escape the surface of a metal

when the energy it gains from a photon exceeds the work function of the metal

evidence that electrons have a particle-like nature

electrons in a beam can be deflected by a magnetic field

de Broglie's hypothesis

matter particles have a dual wave-particle nature, + the wave-like behaviour of a matter particle is characterised by its de Broglie wavelength

how is de Broglies wavelength related to the momentum of the particle

by the equation wavelength = Planck's constant / momentum, or h / mv

how can the de Broglie wavelength of a particle be changed

by changing the velocity of the particle

why does the de Broglie wavelength of an electron become smaller when it moves to an orbit where it travels faster

because its momentum becomes greater

what happens to a narrow beam of electrons in a vacuum tube when it is directed at a thin metal foil

the rows of atoms in the metal cause the electrons in the beam to be diffracted, just as a beam if light is diffracted when it passes through a slit - only diffracted in certain directions

why does a beam of electrons form a pattern of rings on a fluorescent screen when they pass through a thin metal foil

each ring is due to electrons diffracted by the same amount from grains of different orientations, at the same angle to the incident beam

how is the beam of electrons produced for de Broglie's hypothesis experiment

by attracting electrons from a heated filament wire to a positively charged metal plate, which ahs a small hole at its centre that electrons pass through

how can you increase the speed of the electrons in de Broglie's hypothesis experiment

by increasing the pd between the filament and the metal plate

what is the effect of increasing the speed of the electrons in de Broglie's hypothesis experiment

it makes the diffraction rings smaller, because the increase of speed makes the de Broglie wavelength smaller, so less diffraction occurs