Chapter 40 Flashcards
Electron Transitions (photon radiation)
Pauli Exclusion Principle
- A very important physics principle forbids any two electrons to occupy the same quantum state. This is called the Pauli principle.
- Each electron must occupy a unique state defined by a unique set of quantum numbers:
Why does orbitals do not fill up in the expected order according to energy levels
This is because (for example) the 3π^6 4π ^2 configuration results in a lower energy state for the atom than 3π^8
Total energy of an electron on shell n:
When doesnt this equation apply
For π>1, because of electron shielding.
For π>1 what equation do we use to calulate energy in electron shell
The effective charge is equal to the
atomic number (all the protons) minus the shielding effect, π.
π=πβπ
K_πΌ electron transitions energy of the emitted photon is given by:
πΏ_πΌ transitions the energy of the emitted photon is given by:
Electron tranistion summary
Electron tranistion summary
Moseley Equation
Moseley Equation
Three possible ways to obtain EM radiation from atoms
- Excitation β De-excitation of electrons
- Knock an electron out of orbit
- Bremsstrahlung
Excitation β De-excitation of electrons
shine light on the material, or heat the material, thereby causing the electrons to jump to higher energy levels. Once the energy source is removed, the electrons will de-excite (they always seek to be in the lowest energy state) and emit radiation/photons
Knock an electron out of orbit
direct a beam of electrons at an atom. Some electrons will be knocked out of orbit, leaving βholesβ. Electrons in higher energy levels will move to these lower energy levels (they always seek to be in the lowest energy state) and emit radiation/photons.
Brehmsstrahlung
An accelerating electron emits radiation (Larmor Radiation)
When an electron approaches the negatively charged βelectron cloudβ of an atom it slows down (it brakes!). During this deceleration it emits radiation
Therefore:
1. Small acceleration β low energy radiation
2. Large acceleration β high energy radiation
literally thousands of applications:
Laser cutters (e.g. cuts car frames)
Fibre optics
CD/DVD player
Sensitive measuring devices
Why are lasers so useful
- Monochromatic
- Coherent
- Directional
Three important processes of lasers
- Absorbtion
- Spontaneous emission
- Stimulated Emission:
Three important processes of lasers
- Absorbtion
- Spontaneous emission
- Stimulated Emission:
absorbtion
electron absorbs a photon and βjumps upβ to an excited state.
Spontaneous emission
Electron spontaneously de-excites, and releases a photon
Spontaneous emission
Electron spontaneously de-excites, and releases a photon
Stimulated Emission:
Electron de-excites as a result of a stimulus. The stimulus is an external photon. This is weird! It is a similar process to βabsorbtionβ, but the electron de-excites
Stimulated Emission:
Electron de-excites as a result of a stimulus. The stimulus is an external photon. This is weird! It is a similar process to βabsorbtionβ, but the electron de-excites
types of atomic transitions
Lifetime of electrons
When one (or more) electron(s) are not in their lowest possible energy state, we say that an atom is in an excited state. We donβt know when a particular electron will de-excite. In other words, the lifetime of the excited state of a particular atom cannot be predicted
equation to find out how many atoms are in excited state
If π_0 is the number of atoms in an excited state at π‘=0, then at some time, π‘, later we have π(π‘)=π_0 π^((βππ‘) ) atoms in an excited state. Different atoms (e.g. π», π»π, πΏπ) have different lifetimes; i.e. different decay constants π
Half life
The time it takes for half of a large collection of atoms to de-excite to their ground state
Derviving half life equation
