Glossary
Binding Energy
The energy required to remove an electron from a specific energy level or subshell of an atom; higher values indicate electrons closer to the nucleus.
Example:
On a PES spectrum, the peak with the highest binding energy corresponds to the 1s electrons, which are most strongly attracted to the nucleus.
Core electrons
Electrons located in the inner shells of an atom, closer to the nucleus, and are not involved in chemical bonding.
Example:
In a sodium atom (1s²2s²2p⁶3s¹), the 1s², 2s², and 2p⁶ electrons are considered core electrons.
Electron Configuration
A notation that describes the arrangement of electrons in an atom's energy levels and subshells.
Example:
The electron configuration for oxygen is 1s²2s²2p⁴, showing how its 8 electrons are distributed.
Electrons
Negatively charged subatomic particles that orbit the nucleus in specific energy levels and are responsible for chemical bonding.
Example:
In a neutral atom, the number of electrons equals the number of protons, balancing the charge.
Energy Levels (n)
Discrete regions around the nucleus where electrons can be found, with higher numbers indicating greater distance and energy.
Example:
An electron transitioning from the n=3 to the n=2 energy level in a hydrogen atom emits light, forming part of its emission spectrum.
Frequency (ν)
The number of wave cycles that pass a fixed point per unit of time, directly proportional to the energy of a photon.
Example:
High-energy X-rays have a much higher frequency than visible light, which is why they can penetrate soft tissues.
Heisenberg's Uncertainty Principle
States that it is impossible to simultaneously know with perfect accuracy both the position and momentum of a particle, such as an electron.
Example:
Due to Heisenberg's Uncertainty Principle, we talk about the probability of finding an electron in a certain region, not its exact location.
Intensity
The height or relative area of a peak on a PES spectrum, which is proportional to the number of electrons in that particular subshell.
Example:
If a peak on a PES spectrum has an intensity twice that of another peak, it indicates that subshell contains twice as many electrons.
Neutrons
Neutral subatomic particles found in the nucleus of an atom, contributing to its mass but not its charge.
Example:
Isotopes of an element, like Carbon-12 and Carbon-14, differ only in their number of neutrons.
Photoelectric Effect
The phenomenon where electrons are ejected from a metal surface when light of a sufficiently high frequency shines on it.
Example:
Solar panels utilize the photoelectric effect to convert sunlight into electrical energy.
Photoelectron Spectroscopy (PES)
An analytical technique that uses the photoelectric effect to measure the binding energies of electrons in atoms, ions, or molecules, providing information about electron configurations.
Example:
A Photoelectron Spectroscopy spectrum can reveal the number of electrons in each subshell and their relative energies within an atom.
Photon
A discrete packet or quantum of light energy, exhibiting both wave-like and particle-like properties.
Example:
When a photon of sufficient energy strikes a metal surface, it can eject an electron, demonstrating the photoelectric effect.
Protons
Positively charged subatomic particles found in the nucleus of an atom.
Example:
The number of protons in an atom's nucleus determines its atomic number and thus its identity as a specific element, like carbon always having 6.
Quantum-Mechanical Model
A model that describes electrons as existing in probability clouds (orbitals) rather than fixed orbits, based on wave-particle duality.
Example:
The quantum-mechanical model explains why we can't precisely know both an electron's position and momentum simultaneously.
Subshells (s, p, d, f)
Subdivisions within electron energy levels, each capable of holding a specific maximum number of electrons (s=2, p=6, d=10, f=14).
Example:
The 2p subshell can hold up to 6 electrons, influencing an element's chemical reactivity.
Threshold Frequency
The minimum frequency of light required to eject an electron from a particular metal surface in the photoelectric effect.
Example:
If the light's frequency is below the threshold frequency, no electrons will be emitted, no matter how intense the light.
Valence electrons
Electrons located in the outermost shell of an atom, which are primarily involved in chemical bonding and determine an element's reactivity.
Example:
For an element like carbon (1s²2s²2p²), the 2s² and 2p² electrons are its valence electrons, totaling four.