Atomic Structure, the Periodic Table, and Nuclear Chemistry

Vocabulary flashcards covering atomic structure, subatomic particles, periodic trends, element classifications, nuclear reactions, and the Law of Conservation of Mass.

Anion

A negatively charged ion formed when an atom gains electrons.

Cation

A positively charged ion formed when an atom loses electrons.

Atom

The basic unit that makes up matter, consisting of a nucleus, protons, neutrons, and electrons.

Atomic Number

The number of protons in an atom, which identifies the element and equals the number of electrons in a neutral atom.

Mass Number

The total sum of protons and neutrons in an atom's nucleus.

Average Atomic Mass

The weighted average of the masses of all naturally occurring isotopes of an element, typically expressed with a decimal.

Proton

A positively charged particle located in the nucleus with a mass of $1\,\text{amu}$, which determines the element's identity.

Neutron

An electrically neutral subatomic particle located in the nucleus with no charge and a mass of $1\,\text{amu}$, responsible for holding the nucleus together.

Nucleus

The extremely dense, positively charged core of an atom that contains protons and neutrons and accounts for most of the atom's mass.

Electron Cloud

The region surrounding the nucleus that contains electrons, accounts for most of the volume of the atom, and is divided into energy levels or orbitals.

Energy Level

A shell or orbital region within the electron cloud surrounding the nucleus; atoms can possess up to $7$ energy levels.

Valence Electrons

Electrons located in the outermost energy level of an atom that determine how the element reacts chemically with other elements.

Octet Rule

The principle stating that most atoms form bonds by gaining, losing, or sharing electrons in order to achieve a full outer energy level containing $8$ electrons (or $2$ for Hydrogen and Helium).

Period

A horizontal row on the periodic table; there are $7$ periods, and the period number corresponds to the number of energy levels in an atom.

Periodic Law

The principle stating that the chemical and physical properties of elements change predictably as you move across a period.

Family (Group)

A vertical column on the periodic table containing elements that possess the same number of valence electrons and exhibit similar physical and chemical properties.

Transition Metals

The metallic elements located in Groups $3$ through $12$ of the periodic table, which have no simple pattern for valence electrons.

Metal

An element located to the left of the metalloids that is shiny, ductile, malleable, solid at room temperature (except liquid mercury), and a good conductor of heat and electricity.

Metallic Luster

The characteristic shiny appearance displayed by metallic elements.

Metallic Bonding

A type of chemical bonding where positively charged metallic ions are surrounded by a shared sea of mobile electrons.

Nonmetal

An element located to the right of the metalloids that is a poor conductor of heat and electricity, lacks metallic properties, is dull and brittle or powdery as a solid, and tends to gain or share electrons.

Metalloid

An element located along the stair-step line on the periodic table that possesses intermediate properties of both metals and nonmetals and can form both ionic and covalent bonds.

Semiconductor

An element, such as silicon, that can conduct electrical currents only under certain specific conditions.

Isotope

Atoms of the same element that contain the same number of protons but different numbers of neutrons, resulting in different mass numbers.

Stable Isotopes

Isotopes whose atomic nuclei never undergo spontaneous change or decay.

Radioactive Isotopes

Isotopes with unstable nuclei that break down or decay spontaneously, releasing significant amounts of energy.

Radioactivity

The spontaneous emission of radiation from an unstable atomic nucleus.

Half-life

The amount of time required for half of the atoms in a sample of a radioactive isotope to decay.

Transmutation

The transformation of one chemical element into another through a nuclear reaction.

Chain Reaction

A self-sustaining series of nuclear reactions where products from one reaction initiate further reactions.

Nuclear Fission

The process in which a heavy atomic nucleus splits apart into smaller nuclei, releasing energy and neutrons; utilized practically in nuclear power plants.

Nuclear Fusion

The nuclear process where two lighter atomic nuclei combine at extremely high temperatures (millions of degrees Celsius) to form a heavier nucleus, powering stars like the Sun.

Alpha Decay

A form of radioactive decay in which an unstable nucleus emits an alpha particle ($2$ protons and $2$ neutrons), decreasing the atomic number by $2$ and the mass number by $4$.

Beta Decay

A form of radioactive decay involving the emission of an electron-like particle, causing a neutron to become a proton and increasing the atomic number by $1$.

Gamma Decay

The release of high-energy electromagnetic light waves from an atomic nucleus that does not alter either the atomic number or the mass number.

Law of Conservation of Mass

A foundational scientific law stating that matter cannot be created or destroyed, meaning the total mass of reactants must equal the total mass of products in a chemical reaction.

Mikhail Lomonosov

The Russian scientist who first proposed the Law of Conservation of Mass in 1748.

Antoine Lavoisier

The scientist who formulated a more precise scientific description of the Law of Conservation of Mass in 1780 (recorded as Antoine Lavasier).