atomic Flashcards
Bohr’s first pstulate
Electrons move in circular orbits about the nucleus under the influence of coulomb attraction, obeying classical mechanics –> exsistence of the nucleus
bohrs 2nd postulate
an electron can only move in an orbit for which its orbital angular momentum L is an intergral multiple of hbar (hbar=h/2pi)
L=nhbar n is a integer
–> introduces quantisation
bohrs third postulate
the electron is stable in its orbit: constant energyy E and does not radiate
–> removes problem of stability ( by stating that this law of classical mechanics does not apply)
bohrs fourth postulate
absoption and emission are possible through the movement of an electron between two stable orbits and a and b. Radiation frequency , v, of absoption/emission given by
v_ab = (Ea-Eb)/h
–>, basically einsteins postualte v=E/h
what did sommerfeld do
observed high resolution spectra lines and took inspiration from Bohr’s model to derive an extension on this model
what does the sommerfeld extension allow
elliptical orbits as well as circular orbits . All orbits have the same energy. This is keplers law of Ellipses. sommerfeld stated that it is also true for atoms
what does k do
distinguish between elliptical and circular orbits.
orbital angular momentum quantum numbers
l=0 s sharp
l=1 p principle
l=2 d diffuse
l=3 f fundamental
atoms in a uniform magnetic field
will experience Zeeman effect
atoms in a non-uniform magnetic field
will undergo displacement–> stern Gerlachh effect
the zeeman effect (what did he observe)
that when placed in a magnetic field, an atom’s emission spectrum contains lines that arre split into several components.
what is the zeeman effect
it is the splitting of atomic energy levels and the associated spectral lines that result when the atoms are placed in a magnetic field
what did the stern-gerlach experiment show
it provided direct proof that the z component of the magnetic dipole moments of atoms is quantised. space qunatisation
what did the stern-gerlach experiment involve
the experiment involves directing a beam of silver atoms (produced by a hot oven) through a non-uniform magnetic field. the beam is collimated by an aperture before entering a magnet that produces a magnetic field that increasses in intensity in the z direction
what was the result of the stern gerlach experiment
he found that the beam is split into two components, one in the +z direction and the other in the -z direction
spin-orbit interaction
an internal magnetic field is associated with the electrons orbital angular momentum.
spin orbit coupling
The electron is acted on by a strong internal magnetic field, the orientation of which is determined by L. This produces a torque on its spin magnetic dipole moment, the orientation of which is determined by S. This torque casuses L and S to couple together known as spin orbit coupling
define total angular momentum J
J=L+S
Pauli Exclusion Principle
A state specified by the quantum number n,l,m can be occupied by at most two electrons, one with spin up and the other with spin down.
why do doublets occur
due to the smaller spliiting caused by the psin-orbit interaction . The 3p level is split into j =3/2 and j =1/2 states
Normal zeeman effect
Occurs for atomic systems with zero total spin angular momentum
an applied magnetic field couples tothe total orbital angular momentum
the levels split by an amount determined by a constant and hte magnetic quantum number m
Anomalous Zeeman effect
occurs for atomic systems that have atotal spin angular momentum
this caues a different splitting ratio in different levels leading to the observation of more that three components to a transition.
Emission spectra
: An emission spectrum is composed of a series of discrete spectral lines.
Each line arises from a specific transition between two bound states as an excited
electron de-excites to a lower energy level resulting in the emission of a photon.
absoption spectra
An absorption spectrum consists of a continuum with narrow dark lines
appearing at specific wavelengths. These absorption lines arise after a photon is
absorbed, exciting an electron from a lower energy level to a bound upper state
production of optical spectra lines
Optical spectral lines occur when an outer (valence) electron makes a
transition between two bound states causing the emission of a photon.
production of xray spectral lines
X-ray spectra correspond to states of inner or ‘core’ electrons which are bound in
filled shells
Absorption
absorption of a photon takes the atom from a lower energy level E1 to a energetically higher energy level E2. A photon with Delta E= E2-E1=hv is removed from the radiation field
spontaneous emission
An electron in a higher energy state, E2 dexcites to a lower energy state E1. spontaneously emitting a photon of specific energy E to the radiation field
stimulated emission
emission of photon by atom under the influence of applied radiation field. Two photons result from interaction of a single incoming photon. The ‘new’ photon has the same phase and frequency and travels in the same direction as the incoming photon.
what is an absoption edge in an xray spectroscopy
absorption edges are quantum at which the absorption coefficeient jumps to a higher energy value. These edges correspond to the series limits for the K, L , M …, series. The sub shells also appear as edges.
