- The Bohr Model is a planetary model in which the negatively-charged electrons orbit a small, positively-charged nucleus similar to the planets orbiting the Sun (except that the orbits are not planar).
- The typical hydrogen atom has one proton, one electron and no neutrons
- The lowest energy level, n=1, is the “ground state” for the electron to reside in
- If the electron goes to a state higher than the ground state, it is an excited state
- An electron can also drop to a lower energy state, releasing a photon
- The photon energy will be equal to the energy lost by the atom
- A quantum mechanical system or particle that is bound—that is, confined spatially—can only take on certain discrete values of energy, called energy levels. This contrasts with classical particles, which can have any amount of energy.
- Energy levels are a little like the steps of a staircase
Energy Levels of Electrons
- Higher energy levels are less negative
- Negative energies refer to bound electrons
- A material’s absorption spectrum is the fraction of incident radiation absorbed by the material over a range of frequencies.
- Absorption spectroscopy refers to spectroscopic techniques that measure the absorption of radiation, as a function of frequency or wavelength, due to its interaction with a sample.
- An emission spectrum shows the emitted light with a prism
- The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to an atom or molecule making a transition from a high energy state to a lower energy state.
- Emission is the process by which a higher energy quantum mechanical state of a particle becomes converted to a lower one through the emission of a photon, resulting in the production of light. The frequency of light emitted is a function of the energy of the transition.
- Quantum numbers describe values of conserved quantities in the dynamics of a quantum system. In the case of electrons, the quantum numbers can be defined as “the sets of numerical values which give acceptable solutions to the Schrödinger wave equation for the hydrogen atom”.
Pauli Exclusion Principle
- The Pauli exclusion principle is the quantum mechanical principle which states that two or more identical fermions cannot occupy the same quantum state within a quantum system simultaneously.
- No two electrons can have the same 4 quantum numbers
- An orbital is a wave function for an electron defined by the three quantum numbers, n, ℓ and ml. Orbitals define regions in space where you are likely to find electrons.
- The electron configuration is the distribution of electrons of an atom or molecule in atomic or molecular orbitals.
- Magnetism is a class of physical phenomena that are mediated by magnetic fields. Electric currents and the magnetic moments of elementary particles give rise to a magnetic field, which acts on other currents and magnetic moments.
- Non-magnetic materials can respond to magnetic fields
- Diamagnetism is a quantum mechanical effect that occurs in all materials; when it is the only contribution to the magnetism, the material is called diamagnetic. In paramagnetic and ferromagnetic substances the weak diamagnetic force is overcome by the attractive force of magnetic dipoles in the material.
- Induced repulsion force, electrons usually paired
- Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field.
- Induced attractive force, usually unpaired electron
Effective Nuclear Charge
- The effective nuclear charge is the net positive charge experienced by an electron in a polyelectronic atom.
- the uncertainty principle (also known as Heisenberg’s uncertainty principle) is any of a variety of mathematical inequalities asserting a fundamental limit to the precision with which certain pairs of physical properties of a particle, known as complementary variables or canonically conjugate variables such as position x and momentum p, can be known or, depending on interpretation, to what extent such conjugate properties maintain their approximate meaning, as the mathematical framework of quantum physics does not support the notion of simultaneously well-defined conjugate properties expressed by a single value.
- The photoelectric effect is the emission of electrons or other free carriers when light hits a material. Electrons emitted in this manner can be called photoelectrons. This phenomenon is commonly studied in electronic physics and in fields of chemistry such as quantum chemistry and electrochemistry.