Atomic Theory, Periodic Table, and Electron Configuration Vocabulary

Comprehensive vocabulary flashcards covering atomic structure, historical models, chemical symbolism, periodic law, electron configurations, and periodic trends based on lecture notes.

Atom

The smallest structural unit of an element, composed of a dense central nucleus surrounded by electrons.

Electron

A negatively charged subatomic particle located outside the nucleus with a charge of $-1$ and a mass of approximately $5.4 \times 10^{-4}\,amu$ ($9.1095 \times 10^{-28}\,g$).

Proton

A positively charged subatomic particle located in the nucleus with a charge of $+1$ and a mass of approximately $1.0\,amu$ ($1.6725 \times 10^{-24}\,g$).

Neutron

An uncharged subatomic particle found in the nucleus with a mass of approximately $1.0\,amu$ ($1.6750 \times 10^{-24}\,g$), discovered by James Chadwick in 1932.

Dalton's Atomic Theory

The first experimentally based theory of atomic structure, stating that matter consists of tiny indivisible atoms, atoms of a given element are identical, atoms combine in whole-number ratios to form compounds, and chemical changes rearrange atoms.

Law of Conservation of Matter

The principle stating that matter and its total mass remain constant during a chemical change because atoms are neither created nor destroyed.

Law of Definite Proportions

The law formulated by Joseph Proust stating that all samples of a pure compound contain the same elements in the same fixed proportion by mass.

Law of Multiple Proportions

The law stating that when two elements react to form more than one compound, a fixed mass of one element reacts with masses of the other element in small whole-number ratios.

Cathode Rays

Streams of negatively charged particles generated in a high-voltage near-vacuum tube, used to discover electrons and measure their charge-to-mass ratio.

Plum Pudding Model

An early model of the atom proposed prior to Rutherford's work, describing negative electrons embedded throughout a uniform sphere of positive mass.

Gold Foil Experiment

An experiment conducted by Ernest Rutherford firing alpha particles at thin gold foil, demonstrating that atoms consist mostly of empty space with a tiny, dense, positively charged nucleus.

Atomic Number ($Z$)

The number of protons in an atom's nucleus, which uniquely defines the identity of an element.

Mass Number ($A$)

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

Isotopes

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

Deuterium

The isotope of hydrogen containing $1$ proton, $1$ electron, and $1$ neutron ($\text{Hydrogen-2}$ or $^2_1\text{H}$).

Tritium

The isotope of hydrogen containing $1$ proton, $1$ electron, and $2$ neutrons ($\text{Hydrogen-3}$ or $^3_1\text{H}$).

Ion

An atom or group of atoms that carries an overall electrical charge due to the loss or gain of one or more electrons.

Cation

A positively charged ion formed when an atom loses one or more electrons.

Anion

A negatively charged ion formed when an atom gains one or more electrons.

Periodic Law

The principle stating that the chemical and physical properties of the elements repeat periodically when arranged in order of increasing atomic number.

Period

A horizontal row of elements in the periodic table.

Group

A vertical column of elements in the periodic table (also called a family) that share similar physical and chemical properties.

Metals

Elements that conduct heat and electricity well, are shiny and malleable, and tend to lose electrons to form positive ions.

Nonmetals

Elements that are poor conductors of heat and electricity and tend to gain electrons during chemical reactions to form negative ions.

Metalloids

Elements positioned along the stair-step line of the periodic table that possess properties intermediate between those of metals and nonmetals.

Alkali Metals

The Group I elements (excluding hydrogen) that react vigorously with water to form basic alkaline solutions and yield $+1$ cations.

Alkaline Earth Metals

The Group II elements that react with water to form basic solutions and form $+2$ cations.

Transition Metals

Elements in Groups 3-12 (Groups IIIB-VIIIB, IB, IIB) that conduct heat and electricity, are malleable, and frequently form multiple cations with variable charges.

Halogens

Highly reactive Group VII (Group 17) nonmetals that readily gain $1$ electron to form $-1$ anions and exist naturally as diatomic molecules ($\text{F}_2$, $\text{Cl}_2$, $\text{Br}_2$, $\text{I}_2$).

Noble Gases

Virtually inert Group VIII (Group 18) elements that do not readily form compounds because they possess a completely filled valence electron shell.

Quantized Energy

The quantum mechanical concept stating that an electron in an atom can exist only in specific discrete energy levels rather than a continuous spectrum.

Ground State

The lowest and most stable energy state of an electron in an atom.

Excited State

A higher energy state attained when an electron absorbs energy and jumps from its ground state level.

Principal Quantum Number ($n$)

An integer value ($n = 1, 2, 3, \dots$) designating an electron's main energy level or shell, where larger values correspond to greater distance from the nucleus and higher energy.

Energy Subshell

A subunit of a principal energy level categorized as $s$, $p$, $d$, or $f$, which increase in energy in the order $s < p < d < f$.

Orbital

A region of space within a subshell where there is a high probability of finding an electron, holding a maximum of $2$ electrons with opposite spins.

Pauli Exclusion Principle

The rule stating that an orbital can accommodate at most $2$ electrons, and they must possess opposite spins.

Aufbau Principle

The rule guiding electron configuration that dictates electrons fill the lowest-energy orbitals available before occupying higher-energy orbitals.

Hund's Rule

The rule stating that orbitals of equal energy in a subshell are each occupied by one electron with parallel spin before any orbital receives a second paired electron.

Electron Configuration

The representation showing the arrangement of electrons within an atom's shells, subshells, and orbitals.

Valence Electrons

The electrons located in an atom's outermost principal energy level ($n$) that participate in chemical bonding.

Octet Rule

The principle stating that atoms lose, gain, or share electrons during reactions to achieve a stable outer shell of $8$ valence electrons, matching the configuration of the nearest noble gas.

Isoelectronic

Describing atoms or ions that possess the exact same total number of electrons and identical electron configurations.

Atomic Size

A periodic property that increases moving down a group due to additional electron shells and decreases moving left-to-right across a period due to increasing positive nuclear pull.

Ionization Energy

The amount of energy required to remove an electron from an isolated neutral atom in the gas phase.

Electron Affinity

The energy released when an electron is added to an isolated neutral atom in the gas phase to form an anion.