Quantum mechanics is a fundamental theory in physics that describes nature at the smallest scales of atoms and subatomic particles. It explains phenomena such as black-body radiation, the photoelectric effect, and atomic spectra. Quantum mechanics has been hugely successful in explaining many features of the universe. It is often the only theory that can reveal behaviors of subatomic particles like electrons, protons, neutrons, and photons that make up all forms of matter. Quantum mechanics also influences string theory and provides insights into chemical bonding processes through quantum chemistry.

1. Definition of QuantumMechanics
Quantum mechanics (QM; also known as quantum physics ,quantum theory,
the wave mechanical model, or matrix mechanics), including quantum field
theory, is a fundamental theory in physics which describes nature at the
smallest scales of energy levels of atoms and subatomic particles Quantum
mechanics has had enormous[83] success in explaining many of the features of
our universe. Quantum mechanics is often the only theory that can reveal the
individual behaviors of the subatomic particles that make up all forms of matter
electrons, protons, neutrons, photons, and others). Quantum mechanics has
strongly influenced string theories, candidates for a Theory of
Everything (see reductionism. The other great theory of modern physics. Deals
with very small objects. Electrons, atoms, molecules. Grew out of problems that
seemed simple .Black-body radiation
Photoelectric Effect .Atomic Spectra. Quantum mechanics has had enormous
[83] success in explaining many of the features of our universe. Quantum
mechanics is often the only theory that can reveal the individual behaviors of
the subatomic particles that make up all forms of matter
(electrons, protons, neutrons, photons, and others). Quantum mechanics has
strongly influenced string theories, candidates for a Theory of
Everything (see reductionism.
Quantum Mechanics Application Continued
Quantum mechanics is also critically important for understanding how individual
atoms are joined by covalent bond to form molecules. The application of
quantum mechanics to chemistry is known as quantum chemistry. Quantum
mechanics can also provide quantitative insight into ionic and covalent
bonding processes by explicitly showing which molecules are energetically
favorable to which others and the magnitudes of the energies
involved.[84] Furthermore, most of the calculations performed in
modern computational chemistry rely on quantum mechanics
Black Body Radiation: Blackbody Radiation Light emitted by hot
object. Depends only on temperature. Characteristic spectrumof
light. Model of Black Model Radiation: Imagineobjectas box with
“oscillators” in walls Small amountof light leaks out blackbody
spectrum. Light: Electromagnetic waveextremely regular oscillation
No moving parts.
Standing Wave: Standing wave” integer number of half-wavelengths
fit across the length of the box (Rayleigh-Jeans approach;slightly
different than Planck, but simpler.

2.  Photoelectric Effect: Shine light on some object, electrons come
out.Discovered by Heinrich Hertz, 1887
Simple model: Shaking electrons. Predict: 1) Number of ejected
electrons depends on intensity.2) Energy of ejected electrons
depends on intensity 3) No obvious dependence on frequency.
Photoelectric Effect: Einstein:
 1) Number of electrons depends on intensity higher intensity More
quanta. 2) Energy of electrons DOES NOTdepend on intensity. Only
one photon to eject.3) Cut-off frequency: minimum frequency to get
any emission4) Abovecut-off, energy increases linearly with
frequency
Bohr Model:
1913: Neils Bohr comes up with “solar system” model
1) Electrons orbit nucleus in certain “allowed states”
2) Electrons radiate only when moving between allowed states
3) Frequency of emitted/absorbed light determined by Planck rule
è Works greatfor hydrogen, butno reason for ad hoc assumptions.
Atomic Spectra Atoms emit light at discrete, characteristic
frequencies Observed in 1860’s, unexplained until 1913.
Assignment
Quantum Mechanics
Name WAQAR AHMAD KHAN
Department Chemistry 1st
Semester
Sarhad University Of Science And Technology,Peshawar
Submitted To Prof.Khurishid Sir