Dictionary tag: E

Energy Levels

• Imagine electrons orbiting the nucleus of an atom like planets around the sun.
• Each electron occupies a specific energy level, similar to how planets exist in distinct orbits.
• These levels are quantized, meaning they have specific allowed values and electrons cannot freely exist between them.

Excitation

• Electrons can absorb energy from various sources like light, heat, or electrical fields.
• This energy “boosts” them to a higher energy level, similar to a planet receiving a push and moving further from the sun. This process is called excitation.

De-excitation

• Excited electrons are unstable and want to return to their lower energy (ground state) like a planet settling back into its original orbit.
• When they do, they release the excess energy in the form of light, heat, or other forms of radiation.

Types of Transitions

• Absorption: An electron absorbs energy and moves to a higher level.
• Emission: The electron releases energy and moves to a lower level.
• Non-radiative transition: Electron loses energy without emitting light, often through collisions with other atoms.

About shells & orbitals

Shells

• Think of shells as regions around the nucleus where electrons are most likely to be found. These regions are like “zones” or “areas” within the atom, organized according to their energy levels.
  • Shells are labelled using letters (K, L, M, N, etc.) starting from the nucleus outwards. Each shell has a specific energy, with the K shell being closest to the nucleus and having the lowest energy, followed by L, M, and so on.
  • Imagine them as concentric circles around the nucleus, with outer shells being like bigger “orbits” further away.

Orbitals

• Within each shell, electrons occupy specific orbitals, which are subregions of probability where an electron is most likely to be found. These orbitals are like specific “paths” or “locations” within each shell.
  • While the shell gives a general region, the orbital pinpoints the specific area where the electron spends most of its time.
  • Each shell can hold a specific number of electrons depending on its shape and energy level.

Connecting Shells and Orbitals to Energy Levels

• Each shell and orbital has a unique energy level. Electrons in lower shells (closer to the nucleus) and orbitals have lower energy levels than those in higher shells and orbitals. This is because they experience a stronger attraction from the positively charged nucleus, holding them closer and requiring more energy to escape.
• Electron transitions typically happen between orbitals in different shells or within the same shell but with different energy levels. When an electron absorbs energy, it jumps to a higher-energy orbital (excitation). When it releases energy, it moves to a lower-energy orbital (de-excitation).

Example

• Imagine a carbon atom with six electrons. Two electrons are in the lowest energy K shell (1s orbital). The remaining four electrons occupy the L shell, two in the lower-energy 2s orbital and two in the slightly higher-energy 2p orbitals.
• When a carbon atom absorbs light, one of the electrons in the 2s orbital might get excited and jump to an empty 2p orbital, moving to a higher energy level within the same shell.

Key Points

• Shells and orbitals are ways to visualize the location and energy levels of electrons around the nucleus.
• Electrons occupy specific orbitals within shells, with each shell having a unique energy level.
• Electron transitions involve movement between orbitals, driven by absorption or release of energy.

Imagine electrons as tiny magnets with an electric field surrounding them. This electric field affects the space around them.

• When two electrons are close, their electric fields push against each other because they have the same charge (like poles of magnets repel).
• According to the theory of quantum electrodynamics (QED), electrons can’t directly interact with each other. Instead, they exchange energy in the form of a photon, the carrier of the electromagnetic force.
• One electron emits a photon due to a fluctuation in its electric field. This photon carries some energy and momentum.
• The other electron, influenced by the changing electric field of the first electron (carried by the photon), absorbs the photon. This changes the second electron’s energy and momentum.
• So, even though the electrons never directly touch, the exchanged photon acts as a messenger, causing a repulsive force due to the way their electric fields interact.

• Electrons, being charged particles, create an electric field around themselves. When two electrons are present in close proximity, their electric fields interact with each other. This interaction can result in various phenomena, including the exchange of electromagnetic force, exchange of a photon, repulsion or attraction between the electrons, exchange of energy, and momentum transfer.
• This  applies to both real photons, encountered in everyday life, and virtual photons, used as mathematical tools in theoretical physics, is essential for understanding electron-electron interaction:
  • Real photons: Real photons are the ones we encounter in everyday life. They are the carriers of electromagnetic radiation, including visible light, radio waves, microwaves, infrared radiation, ultraviolet radiation, X-rays, and gamma rays. These photons are what we perceive when we see light, feel warmth from the Sun, or use electronic devices that emit or receive electromagnetic signals. Ordinary photons are detectable and observable and form the basis of our understanding of light and electromagnetism.
  • Virtual Photon: Virtual photons are mathematical tools used in theoretical physics, particularly in quantum field theory, to calculate the electromagnetic interaction between charged particles, such as electrons. They are termed “virtual” because they exist as intermediate states in calculations of particle interactions but cannot be directly observed or detected. Virtual photons do not manifest as observable particles in the same way as ordinary photons.
• In some scenarios, electrons can emit or absorb real photons. This can happen during collisions with high enough energy. These real photons can be detected and their properties measured.
• Electron-electron interactions mediated by photons are responsible for many of the properties of matter, such as the electrical conductivity of metals, the colour of objects, and the chemical bonds that hold atoms together.
• More commonly, the interaction happens via virtual photons. These are temporary fluctuations in the electromagnetic field that mediate the force between electrons. They cannot be directly observed because they exist for an extremely short time and violate some properties of real photons (like having no mass).

• Here are four examples of the process of electron-electron interaction mediated by photons:

Colour of objects

• The colour of an object is determined by the wavelengths of light that are absorbed and reflected by the object.
• The absorption and reflection of light is caused by the interaction of photons with electrons in the object. For example, a red object appears red because it absorbs blue and green light, and reflects red photons.

Electrical conductivity of metals

• The electrical conductivity of a metal is determined by the number of free electrons in the metal.
• The free electrons in a metal can be accelerated by an electric field, which causes the metal to conduct electricity. For example, copper is a good conductor of electricity because it has a lot of free electrons.

Møller scattering

• Møller scattering is the name given to electron-electron scattering in quantum field theory.
  • Møller scattering is the process in physics that describes the interaction between two charged particles. It is mediated by the exchange of virtual photons.
  • When two electrons interact with each other through the exchange of a virtual photon, the photon is emitted by one electron and absorbed by the other electron.
  • This exchange of energy and momentum causes the electrons to change their direction of motion. This change in direction is what we observe as the electric force.

Photoelectric emission

• Photoelectric emission is the process of an electron being ejected from a metal surface when light hits the surface. This process can be explained by the exchange of a virtual photon between the electron and the photon. For example, photoelectric emission is used in solar cells to convert sunlight into electricity.

• Electronvolts can be used to measure the energy of elementary particles, including photons, which are the smallest units of electromagnetic radiation (quanta of the electromagnetic field).
  • One electronvolt is equal to the energy gained by a single electron when it is accelerated across a potential difference of 1 volt.
  • Photons (quanta of light) travelling through this same potential difference would also gain 1 eV of energy.
• The electronvolt is not part of the SI unit system. The SI unit for energy is the joule (J). However, joules are too large for many particle-level interactions.
• 1 electronvolt (eV) is equivalent to approximately 1.602 x 10^-19 joules (J).
• The electronvolt is often used in conjunction with metric prefixes to represent energy values at different magnitudes.
  • kiloelectronvolt (keV): 1 keV = 1,000 eV (used for energies of X-rays)
  • megaelectronvolt (MeV): 1 MeV = 1,000,000 eV (used for energies of gamma rays and nuclear reactions)
  • gigaelectronvolt (GeV): 1 GeV = 1,000,000,000 eV (used for energies of particles in particle accelerators)
  • teraelectronvolt (TeV): 1 TeV = 1,000,000,000,000 eV (used for energies of very high-energy particles in cosmic rays)

• The electrostatic force is sometimes called the electric force. Both terms refer to the force that arises between charged particles. The word “electrostatic” emphasizes that the force is due to stationary (static) charges, while the word “electric” is a more general term that encompasses both static and moving charges.
• These two forces, electrostatic and magnetic articulate the behaviour of the electromagnetic field. They reveal that electric and magnetic fields are two facets of a unified electromagnetic field.
• The magnitude of the electrostatic force between two charged particles is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
• The electrostatic force is the force between two electrically charged particles, regardless of whether they are moving or not.
• The magnetic force is the force between two moving electric charges, or between a magnetic field and a moving electric charge.
• The magnetic force is responsible for the attraction between oppositely charged magnets, such as a north pole and a south pole. It is also responsible for the repulsion between like-charged magnets, such as two north poles or two south poles.
• The magnetic force is responsible for the attraction between a magnet and a piece of iron. This is because iron is a ferromagnetic material, which means that it can be magnetized. When a magnet is brought near a piece of iron, the magnetic force of the magnet aligns the magnetic domains in the iron, causing the iron to become temporarily magnetized.
• The electrostatic force and the magnetic force are unified by Maxwell’s equations, which describe the behaviour of the electromagnetic field. Maxwell’s equations show that the electric and magnetic fields are two aspects of the same field and that they are related to each other.
• The electromagnetic force is one of the four fundamental forces of nature. The other three fundamental forces are the strong nuclear force, the weak nuclear force, and gravity. The electromagnetic force is the strongest of the four fundamental forces at the atomic and macroscopic levels.

• Elements are the building blocks of matter.
• Atoms are the particles that elements are composed of.
• Each element consists of a unique type of atom.
• Elements are represented by unique symbols, such as H for hydrogen and O for oxygen.
• Each type of atom has a different number of protons in its nucleus.
• The atomic number of an atom corresponds to the number of protons in its nucleus.
• The Periodic Table is a comprehensive inventory of elements, arranged according to their atomic numbers.
• The Periodic Table categorizes elements with similar properties and reveals trends and patterns in their chemical behaviour.
• Elements combine to form compounds with distinct characteristics and properties.

• A compound is a substance made from the combination of two or more elements and held together by chemical bonds that are difficult to break.
• Compounds have distinct properties that differ from those of their constituent elements.

• In the context of electromagnetism, there is only one elementary particle, the photon, which acts as the force carrier, transmitting the electromagnetic force and carrying energy and momentum.
• One way photons are created and destroyed is through subatomic processes within atoms and molecules.
• These processes often involve interactions between elementary particles governed by the strong nuclear force, which bind the building blocks of atoms (protons and neutrons) together.
• Remember that when photons are created within atoms and molecules through interactions like electron transitions and interactions with the strong nuclear force they produce light.
• Other light producing process (light sources) include: blackbody radiation (incandescent light bulb), nuclear fusion (sunlight), annihilation (gamma rays) and high-energy phenomena (supernovae).

Electromagnetic force

• The photon is the elementary particle associated with the electromagnetic force.
• It has no mass, no electric charge, and always travels at the speed of light in a vacuum.
• Photons carry electromagnetic energy and momentum.
• They are the building blocks of electromagnetic radiation, which encompasses a wide spectrum including light (visible and invisible), radio waves, X-rays, gamma rays, and more.

Strong Nuclear Force

• Gluons (g): These particles mediate the strong nuclear force, which binds quarks together to form protons and neutrons (collectively known as nucleons). Gluons themselves come in eight different “colours” and interact with each other, contributing to the strong force’s complex nature.

Weak Nuclear Force

• W and Z bosons (W⁺, W⁻, Z⁰): These three massive particles are responsible for mediating the weak nuclear force, which is involved in certain types of radioactive decay and some nuclear reactions. Unlike the photon and gluons, W and Z bosons have significant mass and participate in their own interactions.

Gravity (hypothetical)

• Graviton (G): While not yet directly observed, the graviton is the theorized force carrier for gravity. It is expected to be a massless particle with unique properties due to the nature of gravity itself. The search for the graviton is an active area of research in physics.

• Energy Changes in Atoms/Molecules: Atoms and molecules absorb and release energy, causing changes in electron positions or molecular vibrations. This energy is often emitted as electromagnetic radiation.
• Electron Transitions: Electrons jump between specific energy levels within an atom. When they absorb energy, they move to higher levels; when they return to lower levels, they release energy as photons.
• Molecular Vibrations: In molecules, atoms vibrate within chemical bonds. When energy is absorbed, these vibrations increase, and the energy can be emitted as electromagnetic radiation, often in the infrared spectrum.
• Atomic vibrations refer to the back-and-forth movements of individual atoms around their fixed positions. This is often discussed in solid-state physics, where atoms in a solid are arranged in a regular pattern and can oscillate slightly while remaining in place overall.

Types of Emission

• Electromagnetic radiation: The emission of photons, which are the energy packets of light and include electromagnetic waves like X-rays, gamma rays, radio waves, etc.
  • Electrons transition from higher to lower energy levels in atoms, emitting a photon with specific energy.
  • Radioactive nuclei decay, emitting high-energy photons like gamma rays.
• Particle emission: This involves the emission of subatomic particles themselves, such as electrons, neutrons, protons, or alpha particles.
  • Radioactive nuclei decay emits alpha particles or beta particles (electrons or positrons).
  • Neutron stars can emit streams of charged particles in a phenomenon called “pulsar wind.”

Causes of Emission

• Energy transitions: When a subatomic particle transitions from a higher energy state to a lower one, it emits the excess energy as radiation or particles.
• Instability: Radioactive nuclei are unstable and undergo decay to reach a more stable configuration, emitting energy and particles in the process.
• External interactions: Subatomic particles can be struck by other particles or radiation, leading them to emit energy or new particles.

Consequences of Emission

• Most of the light and energy we perceive around us arises from subatomic emission processes in stars, atoms, and molecules.
• Understanding subatomic emission is crucial for studying radioactive materials and designing nuclear reactions for energy production or other purposes.
• Studying the types and properties of emitted particles and radiation from cosmic sources helps us understand the composition and evolution of the universe.

Important concepts

• Quantum mechanics: Governs the behaviour of particles at the subatomic level and explains the probabilities associated with various emission processes.
• Energy levels: Electrons and other particles occupy specific energy levels within atoms. Transitions between these levels can lead to emissions.
• Radioactive decay: Different types of radioactive decay involve different emitted particles and energy levels.

Natural causes of emissions

• Stellar emissions: Stars like the Sun emit across the entire electromagnetic spectrum due to nuclear fusion at their core. This includes visible light, radio waves, infrared, ultraviolet, X-rays, and gamma rays.
• Atmospheric phenomena: Lightning strikes emit electromagnetic radiation, including visible light and radio waves. Aurora borealis and australis (Northern and Southern Lights) produce colourful visible light emissions due to charged particles interacting with the atmosphere.
• Forest fires and volcanic eruptions: These events release smoke, ash, and gases into the atmosphere. These particles scatter and absorb sunlight, impacting Earth’s energy balance. Volcanoes also emit various gases including sulfur dioxide and carbon dioxide.
• Biological processes: Living organisms like plants and animals release gases during respiration and other metabolic processes. These include carbon dioxide, methane, and nitrous oxide, all greenhouse gases contributing to climate change.

Artificial Causes of Emissions

• Fossil fuel combustion: Burning coal, oil, and natural gas for electricity generation, transportation, and industrial processes releases large amounts of greenhouse gases like carbon dioxide and nitrogen oxides, contributing significantly to climate change.
• Industrial processes: Manufacturing industries release various pollutants, including volatile organic compounds (VOCs), sulfur oxides, and particulate matter, impacting air quality.
• Agriculture: Fertilizer use, animal waste management, and agricultural land-use changes contribute to nitrous oxide emissions, a potent greenhouse gas.
• Deforestation: Cutting down trees reduces the carbon sequestration capacity of forests, leading to increased atmospheric carbon dioxide levels.

• Everything contains energy including all forms of matter and so all objects.
• Energy is evident in all forms of movement, interaction, and changes to the forms and properties of matter.
• Energy can exist in different forms, including thermal energy, chemical energy, electrical energy, and nuclear energy.
• At an atomic level, energy is evident for instance in the motion of electrons orbiting the nucleus of atoms.
• Energy can be transferred from one object to another and converted between different forms, but it cannot be created or destroyed.
• Everything in the universe uses energy of one form or another all the time.
• Energy is often described as potential energy or kinetic energy.
• Energy is measured in joules whilst power is measured in joules per second.

• Energy Carried by Photons: Electromagnetic radiation, including light, radio waves, X-rays, etc., consists of packets of energy called photons. The energy carried by a photon is directly related to its frequency. Higher frequencies correspond to higher energy photons.
• Electric Potential Energy: Electrostatic interactions involve the concept of electric potential energy. This energy is associated with the position of charged particles in an electric field. The difference in potential energy between two points determines the amount of work done when a charged particle moves between them.
• Electrical Energy: Electrical energy is the flow of electrical charges through a conductor. This flow of charge can be used to perform various tasks, such as powering lights, motors, and electronic devices. The amount of electrical energy transferred depends on the voltage (potential difference) and current flowing in the circuit.
• Magnetic Fields and Energy: Moving charges or changing electric fields create magnetic fields. Magnetic fields can also store energy. Electromagnets, for instance, use electrical energy to create a magnetic field, which can then be used to perform work, like lifting objects.
• Energy Transfer and Conversion: In electromagnetic interactions, energy can be transferred between different forms. For example, light energy (photons) can be converted into electrical energy in solar cells. Additionally, electrical energy can be used to create magnetic fields, storing energy, or converted into other forms like heat or light.

• Quantum Field Theory proposes a new way of looking at particles. Instead of individual particles existing on their own, it suggests that everything is made of vibrating energy fields that fill all of space and time. These fields are the fundamental entities, not the particles themselves.
• Particles as Excitations: When these fields get “rippled” or excited, they can create temporary bursts of energy that behave like particles. These are the particles we’re familiar with, like electrons or photons (light particles).
• Virtual vs. Real Particles: Some ripples are tiny and fleeting, lasting only a fraction of a second. These are called virtual particles. They can’t be directly detected but influence how real particles interact.
• Real Particles: Stronger ripples can create real particles that exist for longer and have definite properties like location and momentum. These are the particles we can measure in experiments.
• Adding Energy: Anything that adds energy to a field can create these ripples. This energy could come from another particle, an outside force, or even random fluctuations within the field itself.

• As an example imagine the field for light. This is the electromagnetic field. When this field gets a jolt of energy, it can create a ripple that produces a photon, a particle of light.