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Showing 61–90 of 1709 reference entries

Physics · MeasurementElectric current

Current measures charge crossing a chosen surface per unit time.

DefinitionPhysicsElectric field and force

An electric field assigns force per unit test charge.

DefinitionPhysicsMagnetic force on a moving charge

Magnetic force depends on charge motion relative to the field.

ModelPhysicsOhm's law and its domain

A linear current-voltage relation requires suitable conditions.

Empirical findingPhysicsFirst law of thermodynamics

Keep the heat and work sign convention explicit in an energy balance.

ModelPhysicsSecond law: isolated-system entropy

Apply entropy increase to the whole isolated system.

ModelPhysics · ChemistryIdeal-gas equation of state

A simple gas model relates pressure, amount, volume and temperature.

ModelPhysicsPhoton energy and frequency

One photon's energy is proportional to its frequency.

ModelPhysics · Mathematics & logicInvariant spacetime interval

Lorentz transformations preserve a combined space-time separation.

ModelPhysicsNewton's third law

Interaction forces act on different bodies in equal and opposite pairs.

ModelPhysicsAngular momentum and torque

Torque changes angular momentum about a specified origin.

ModelPhysicsHydrostatic pressure

Static fluid pressure rises with depth under gravity.

ModelPhysicsArchimedes' buoyancy principle

The hydrostatic upward force equals displaced-fluid weight.

ModelPhysicsMaxwell equations in free space

Four field equations connect electric and magnetic fields with charge and current.

ModelPhysicsSchrödinger time evolution

A quantum wavefunction evolves according to its Hamiltonian.

ModelPhysicsBorn position probability

A normalized wavefunction assigns probabilities to position intervals.

ModelPhysics · MeasurementElementary charge

The elementary charge has an exact SI numerical value.

DefinitionPhysics · MeasurementBoltzmann constant

The Boltzmann constant has an exact SI numerical value.

DefinitionMeasurement · Chemistry · PhysicsAvogadro constant

The mole is linked to a specified number of entities.

DefinitionMeasurement · PhysicsSI defining luminous efficacy

A specified frequency fixes the photometric SI reference.

DefinitionChemistryAtoms and elemental identity

The proton count of an atomic nucleus identifies its chemical element.

DefinitionChemistryIsotopes and mass number

Isotopes share a proton count but have different neutron counts.

DefinitionChemistryPeriodic organization of the elements

Atomic-number order reveals recurring patterns in electron structure and chemical properties.

ModelChemistryChemical bonds

Bonding describes interactions that bind atoms into molecules or extended structures.

DefinitionChemistry · MeasurementMole and amount of substance

The mole counts specified entities using the exact Avogadro constant.

DefinitionChemistryReaction stoichiometry

Balanced coefficients relate the amounts consumed and produced by a reaction.

MethodChemistryBalancing atoms and electric charge

A chemical equation must preserve each element's atom count and the total charge.

MethodChemistryDynamic chemical equilibrium

At equilibrium, opposing reactions continue without net composition change.

ModelChemistryBrønsted acids and bases

In the Brønsted description, an acid donates a proton and a base accepts it.

DefinitionChemistryGibbs energy and thermodynamic direction

Gibbs-energy change distinguishes thermodynamic favourability from reaction speed.

Model
DefinitionSource checked

Atoms and elemental identity

Chemistry

The proton count of an atomic nucleus identifies its chemical element.

Key knowledge

An atom has a nucleus surrounded by electrons. Its atomic number Z is the number of protons in the nucleus and identifies the element. A neutral atom has the same number of electrons as protons; gaining or losing electrons forms an ion of that element.

Conditions and scope

  • Electron count equals Z only for a neutral atom.
  • This entry concerns ordinary atomic and ionic identity, not nuclear transformations.
Sources · 3

References

Sources retain their recorded scope. A source link alone does not establish verification of every statement.

  1. Chemistry, Unit 2: Structure of Atom — sections 2.2.3–2.2.4National Council of Educational Research and Training (NCERT), IndiaTextbook chapter · PDFncert.nic.inRead source
  2. Chemistry 2e (2019), §2.3 Atomic structure and symbolismPaul Flowers, Klaus Theopold, Richard Langley and William R. Robinson · OpenStax/Rice UniversityTextbook chapteropenstax.orgRead source
  3. Physical Sciences 10: Atomic structureSiyavulaTextbook chaptersiyavula.comRead source

Evidence and review

Documented definitions of atomic number, neutrality and ionic charge; no atomic experiment was repeated.

2026-10-10 · English atomic identity and neutral/ionic distinction checked against NCERT sections 2.2.3–2.2.4 and the adjacent worked examples.

Foundational review

2026-10-10 · Fresh primary-source inspection of the complete compact record, including every statement, equation, quantity and material condition, followed by independent AI editorial review. This check does not certify all linked lessons or every passage of every cited publication.

Sources from other places

Agreement within this scope

Proton identity, nuclear counts and neutral versus ionic electron counts.

Electron changes alter charge; changing proton number changes the element.

Related reference entries

Explore relationships within this area of study and its connections to other areas.

Showing 1–2 of 2 relationships

Scientific relationships · 2 / 2

The relationship type describes the connection. Its linked statements, sources and conditions define the scope.

  1. Related to
    Relationship sources · 1

    Linked statements

    • Isotopes are atoms of the same element with different numbers of neutrons. Their atomic number is the same, while their mass number A, the total number of protons and neutrons, differs.
    • An atom has a nucleus surrounded by electrons. Its atomic number Z is the number of protons in the nucleus and identifies the element. A neutral atom has the same number of electrons as protons; gaining or losing electrons forms an ion of that element.

    Isotope identity uses the shared atomic number of an element.

  2. Related to
    Relationship sources · 2

    Linked statements

    • An element contains atoms of one atomic number; a compound combines elements chemically. A pure substance is one chemical substance, whereas a mixture contains multiple substances. A homogeneous mixture is uniform at the specified observation scale; a heterogeneous mixture is not. A solution can therefore look uniform without being a pure substance.

    Element and compound classification describes composition; atomic structure supplies the underlying atomic-number distinction.

Entry detailsPermanent link to this entry ↗
Record identity
chem-atoms-elements
Revision
core.1
Structured reference record
Essential core · first collection