| Term | Definition |
|---|---|
| atomic mass units | A unit of mass used to express the mass of individual atoms or molecules, where one amu is defined relative to carbon-12. |
| Avogadro's number | The constant 6.022 × 10^23 mol^-1 that represents the number of particles (atoms, molecules, or formula units) in one mole of a substance. |
| constituent particles | The individual atoms, molecules, or ions that make up a substance. |
| dimensional analysis | A mathematical technique for converting between different units of measurement by using conversion factors and canceling units. |
| formula unit | The smallest unit of a compound that shows the fixed proportions of atoms or ions held together. |
| molar mass | The mass in grams of one mole of a substance, numerically equal to the average mass of one particle in atomic mass units. |
| mole concept | A fundamental chemistry concept that relates the number of particles (atoms, molecules, or ions) to measurable quantities through Avogadro's number. |
| Term | Definition |
|---|---|
| average atomic mass | The weighted average of the masses of all isotopes of an element, based on their relative abundances in nature. |
| isotopes | Atoms of the same element that have different numbers of neutrons and therefore different mass numbers. |
| isotopic masses | The mass of individual isotopes of an element, typically expressed in atomic mass units. |
| mass spectrum | A graphical representation showing the masses of isotopes of an element and their relative abundances. |
| relative abundance | The percentage or proportion of each isotope present in a naturally occurring sample of an element. |
| weighted average | A calculation method that accounts for the relative abundance of each isotope when determining the average atomic mass of an element. |
| Term | Definition |
|---|---|
| constituent elements | The individual elements that make up a compound in fixed proportions. |
| elemental composition by mass | The percentage or proportion of each element present in a substance, expressed as a mass fraction or mass percentage. |
| empirical formula | The chemical formula that represents the lowest whole number ratio of atoms of the elements in a compound. |
| formula unit | The smallest unit of a compound that shows the fixed proportions of atoms or ions held together. |
| law of definite proportions | The principle that the ratio of the masses of the constituent elements in any pure sample of a compound is always the same. |
| pure substance | A material with a fixed, definite composition and consistent properties throughout. |
| Term | Definition |
|---|---|
| elemental analysis | An analytical technique used to determine the relative numbers of atoms of each element in a substance and to assess its purity. |
| elemental composition by mass | The percentage or proportion of each element present in a substance, expressed as a mass fraction or mass percentage. |
| mixture | Materials that contain atoms, molecules, or formula units of two or more types, whose relative proportions can vary. |
| pure substance | A material with a fixed, definite composition and consistent properties throughout. |
| purity | The degree to which a substance contains only one type of atom, molecule, or formula unit without contamination from other substances. |
| Term | Definition |
|---|---|
| Aufbau principle | The rule that electrons fill orbitals in order of increasing energy, with lower energy orbitals filled before higher energy orbitals. |
| core electrons | Inner electrons in an atom that are not in the outermost shell and do not participate in bonding. |
| Coulomb's law | The principle that the electrostatic force between charged particles is proportional to the product of their charges and inversely proportional to the square of the distance between them. |
| effective charge | The net positive charge experienced by an electron in an atom, accounting for shielding by inner electrons. |
| electrons | Negatively charged subatomic particles that orbit the nucleus of an atom. |
| ground-state electron configuration | The arrangement of electrons in an atom or ion in its lowest energy state, following the Aufbau principle. |
| ionization energy | The energy required to remove an electron from an atom in the gas phase. |
| neutrons | Neutral subatomic particles found in the nucleus of an atom. |
| nucleus | The positively charged center of an atom composed of protons and neutrons. |
| protons | Positively charged subatomic particles found in the nucleus of an atom. |
| shell | Energy levels in an atom that contain electrons, designated by principal quantum numbers (n = 1, 2, 3, etc.). |
| shielding | The reduction in the effective nuclear charge experienced by outer electrons due to repulsion from inner electrons. |
| subshell | A subdivision of an electron shell characterized by a specific orbital type (s, p, d, or f) and containing orbitals of similar energy. |
| valence electrons | Electrons in the outermost shell of an atom that participate in bonding and determine many properties of substances. |
| Term | Definition |
|---|---|
| electron configuration | The arrangement of electrons in an atom or ion, describing which orbitals and subshells are occupied and how many electrons are in each. |
| ionization energy | The energy required to remove an electron from an atom in the gas phase. |
| photoelectron spectroscopy | An experimental technique that measures the energy required to remove electrons from different subshells of an atom or ion. |
| photoelectron spectrum | A graphical representation of data from photoelectron spectroscopy showing peaks that correspond to electrons in different subshells of an atom or ion. |
| subshell | A subdivision of an electron shell characterized by a specific orbital type (s, p, d, or f) and containing orbitals of similar energy. |
| Term | Definition |
|---|---|
| atomic properties | Characteristics of atoms such as size, ionization energy, electron affinity, and electronegativity that vary predictably across the periodic table. |
| atomic radius | The size of an atom, typically measured as the distance from the nucleus to the outermost electrons. |
| Coulomb's law | The principle that the electrostatic force between charged particles is proportional to the product of their charges and inversely proportional to the square of the distance between them. |
| effective nuclear charge | The net positive charge experienced by an electron in an atom, accounting for shielding by inner electrons. |
| electron affinity | The energy change that occurs when an electron is added to an atom in the gas phase. |
| electron configuration | The arrangement of electrons in an atom or ion, describing which orbitals and subshells are occupied and how many electrons are in each. |
| electronegativity | A measure of an atom's ability to attract valence electrons in a chemical bond; increases across a period and decreases down a group in the periodic table. |
| electronic structure | The arrangement of electrons in an atom, including the distribution across shells and subshells. |
| ionic radius | The size of an ion, which differs from the neutral atom due to the gain or loss of electrons. |
| ionization energy | The energy required to remove an electron from an atom in the gas phase. |
| periodicity | The recurring pattern of properties in elements that repeats across periods and groups in the periodic table. |
| shell | Energy levels in an atom that contain electrons, designated by principal quantum numbers (n = 1, 2, 3, etc.). |
| shell model | A model of atomic structure in which electrons occupy discrete energy levels or shells around the nucleus. |
| shielding | The reduction in the effective nuclear charge experienced by outer electrons due to repulsion from inner electrons. |
| subshell | A subdivision of an electron shell characterized by a specific orbital type (s, p, d, or f) and containing orbitals of similar energy. |
| unpaired electrons | Electrons that occupy orbitals alone rather than in pairs, affecting an atom's magnetic and chemical properties. |
| Term | Definition |
|---|---|
| chemical bond | An attractive force between atoms that holds them together in a compound. |
| ionic charge | The net electrical charge of an ion, determined by the number of valence electrons and the element's position on the periodic table. |
| ionic compound | Compounds formed by the electrostatic attraction between positively charged cations and negatively charged anions. |
| periodic table | A systematic arrangement of elements organized by atomic number and grouped by similar chemical properties. |
| periodicity | The recurring pattern of properties in elements that repeats across periods and groups in the periodic table. |
| reactivity | The tendency of an element to undergo chemical reactions and form bonds with other elements. |
| valence electrons | Electrons in the outermost shell of an atom that participate in bonding and determine many properties of substances. |