Glossary
Anions
Negatively charged ions formed when an atom gains one or more electrons.
Example:
When a fluorine atom gains an electron, it becomes an anion with a -1 charge ().
Atomic Mass
The mass of an atom, predominantly determined by the combined mass of its protons and neutrons.
Example:
The atomic mass of an element on the periodic table is typically a weighted average of its naturally occurring isotopes.
Atomic number
The unique number of protons in an atom's nucleus, which fundamentally defines the element.
Example:
Every atom of oxygen has an atomic number of 8, meaning it always contains 8 protons.
Bohr model
A historical atomic model that describes electrons orbiting the nucleus in specific, quantized energy levels, successfully explaining the hydrogen atom's spectrum.
Example:
The Bohr model predicts the specific wavelengths of light emitted when an electron in a hydrogen atom transitions between energy levels.
Cations
Positively charged ions formed when an atom loses one or more electrons.
Example:
A magnesium atom that loses two electrons forms a cation with a +2 charge ().
Centripetal Force
The net force required to keep an object moving in a circular path, directed towards the center of the circle.
Example:
In the Bohr model, the electric force between the electron and nucleus provides the centripetal force necessary for the electron's stable orbit.
Coulomb's Law
A fundamental law describing the electrostatic force between two charged particles, which is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
Example:
The attractive force holding an electron in orbit around a nucleus is described by Coulomb's Law.
Electron Configuration
The arrangement of electrons in an atom's orbitals and energy levels, which dictates its chemical behavior.
Example:
The stable electron configuration of noble gases explains their low reactivity.
Energy Levels
The specific, allowed energy values that an electron can possess within an atom, corresponding to different orbits or shells.
Example:
When an electron absorbs a photon, it can jump from a lower to a higher energy level within the atom.
Hydrogen atom's discrete energy states
The specific, fixed energy levels that an electron can occupy within a hydrogen atom, as predicted by the Bohr model.
Example:
When an electron in a hydrogen atom jumps between these hydrogen atom's discrete energy states, it absorbs or emits a photon of a precise energy.
Ions
Atoms or molecules that have gained or lost one or more electrons, resulting in a net positive or negative electrical charge.
Example:
When a sodium atom loses an electron, it becomes a positively charged ion ().
Isotopes
Atoms of the same element (same number of protons) that have different numbers of neutrons, leading to variations in atomic mass.
Example:
Uranium-235 and Uranium-238 are isotopes of uranium, differing in their neutron count.
Negatively charged electrons
Subatomic particles that orbit the nucleus of an atom, each carrying a fundamental negative electrical charge.
Example:
The flow of negatively charged electrons through a circuit creates an electric current.
Neutrons
Neutral (no charge) subatomic particles located within the atomic nucleus, contributing to the atom's mass.
Example:
Deuterium, an isotope of hydrogen, has one proton and one neutron in its nucleus.
Nuclear Notation
A symbolic representation of an atomic nucleus, indicating the mass number (protons + neutrons) as a superscript and the atomic number (protons) as a subscript.
Example:
The Nuclear Notation signifies Uranium with 92 protons and a total of 235 protons and neutrons.
Photon emission/absorption
The process by which an atom releases (emits) or takes in (absorbs) a packet of electromagnetic energy (photon) when an electron transitions between energy levels.
Example:
The distinct colors observed in fireworks are a result of specific photon emission/absorption events as electrons in different metal atoms transition between energy levels.
Positively charged nucleus
The central, dense core of an atom containing protons and neutrons, which carries a net positive electrical charge.
Example:
In a helium atom, the two protons and two neutrons form the positively charged nucleus, around which electrons orbit.
Protons
Positively charged subatomic particles found within the atomic nucleus, whose number defines the element's identity.
Example:
An atom with 6 protons is always carbon, regardless of its neutron count.
Quantization
The concept that certain physical quantities, such as energy or angular momentum, can only exist in discrete, specific values rather than a continuous range.
Example:
The quantization of light means that light energy comes in discrete packets called photons.
Standing Wave Model
A model that explains the quantization of electron energy levels by proposing that electrons exist as standing waves around the nucleus.
Example:
The Standing Wave Model suggests that only electron orbits where the de Broglie wavelength fits an integer number of times around the circumference are stable.
Valence electrons
Electrons located in the outermost electron shell of an atom, primarily responsible for chemical bonding and reactivity.
Example:
Silicon's four valence electrons enable it to form strong covalent bonds, making it crucial for semiconductors.