Editing Atomic physics (section)

==Electronic configuration==
Electrons form notional [[Electron shells|shells]] around the nucleus. These are normally in a [[ground state]] but can be excited by the absorption of energy from light ([[photon]]s), [[magnetic field]]s, or interaction with a colliding particle (typically ions or other electrons).

[[File:Bohr atom model.svg|thumb|In the Bohr model, the transition of an electron with n=3 to the shell n=2 is shown, where a photon is emitted. An electron from shell (n=2) must have been removed beforehand by ionization]] Electrons that populate a shell are said to be in a [[bound state]].  The energy necessary to remove an electron from its shell (taking it to infinity) is called the [[binding energy]].  Any quantity of energy absorbed by the electron in excess of this amount is converted to [[kinetic energy]] according to the [[conservation of energy]].  The atom is said to have undergone the process of ionization.

If the electron absorbs a quantity of energy less than the binding energy, it will be transferred to an excited state. After a certain time, the electron in an excited state will "jump" (undergo a transition) to a lower state. In a neutral atom, the system will emit a photon of the difference in energy, since energy is conserved.

If an inner electron has absorbed more than the binding energy (so that the atom ionizes), then a more outer electron may undergo a transition to fill the inner orbital. In this case, a visible photon or a [[characteristic x-ray|characteristic X-ray]] is emitted, or a phenomenon known as the [[Auger effect]] may take place, where the released energy is transferred to another bound electron, causing it to go into the continuum.  The Auger effect allows one to multiply ionize an atom with a single photon.

There are rather strict [[selection rule]]s as to the electronic configurations that can be reached by excitation by light — however, there are no such rules for excitation by collision processes.

===Bohr Model of the Atom===

The Bohr model, proposed by '''Niels Bohr in 1913''', is a revolutionary theory describing the structure of the hydrogen atom. It introduced the idea of quantized orbits for electrons, combining classical and quantum physics.

'''Key Postulates of the Bohr Model'''

'''1. Electrons Move in Circular Orbits:'''

• Electrons revolve around the nucleus in fixed, circular paths called '''orbits''' or '''energy levels'''.

• These orbits are '''stable''' and do not radiate energy.

'''2. Quantization of Angular Momentum:'''

• The angular momentum of an electron is quantized and given by:

:<math>\ L = m_{e}vr = n_{\hbar}, \quad n = 1, 2, 3, \ldots </math>

where:

• <math> m_e : </math> Mass of the electron.

• <math> v : </math> Velocity of the electron.

• <math> r : </math> Radius of the orbit.

• <math> \hbar : </math> Reduced Planck's constant (<math>\hbar = \frac{h}{2\pi}</math>).

• <math> n : </math> Principal quantum number, representing the orbit.

'''3. Energy Levels:'''

• Each orbit has a specific energy. The total energy of an electron in the <math>n</math>th orbit is:

:<math>\ E_n = -\frac{13.6}{n^2} \ \text{eV}, </math>

where <math> 13.6 \ \text{eV} </math> is the ground-state energy of the hydrogen atom.

'''4. Emission or Absorption of Energy:'''

• Electrons can transition between orbits by '''absorbing''' or '''emitting''' energy equal to the difference between the energy levels:

:<math>\ \Delta E = E_f - E_i = h\nu, </math>

where:

• <math> h : </math> Planck's constant.

• <math> \nu : </math> Frequency of emitted/absorbed radiation.

• <math> E_f, E_i : </math> Final and initial energy levels.