General Chemistry: Atomic Theory, Chemical Formulas, and Reaction Stoichiometry

A complete set of vocabulary flashcards covering key terms from Chapters 2, 3, and 4 on atomic structure, naming, formulas, moles, solutions, and reaction stoichiometry.

atomos

Greek term meaning 'indivisible,' proposed by fifth-century BC philosophers Leucippus and Democritus to describe fundamental, indivisible particles of matter.

Law of Conservation of Mass

Principle stating that in any chemical reaction, the total mass of the products formed always equals the mass of the reactants consumed.

Law of Definite Proportions

Also known as the Law of Constant Composition, stated by Joseph Proust in 1799, dictating that all samples of a pure compound contain the same elements in the same proportion by mass.

Law of Multiple Proportions

Formulated by John Dalton in 1803, stating that when two elements combine to form more than one compound, the mass ratios of the combined elements are represented by small whole numbers.

Cathode Ray Tube Experiment

An 1897 experiment conducted by J.J. Thomson demonstrating that cathode rays consist of negatively charged subatomic particles (electrons).

Plum Pudding Model

An early atomic model depicting negatively charged electrons embedded within a positively charged sphere of matter.

Oil-Drop Experiment

A 1909 experiment by Robert Millikan that measured the fundamental electric charge of an electron as $1.6 \times 10^{-19}\text{ coulomb}$.

Alpha Particle ($\alpha$)

A type of radiation composed of a helium nucleus carrying a $+2$ charge.

Beta Particle ($\beta$)

A type of radiation consisting of high-energy electrons carrying a $-1$ charge.

Gamma Ray ($\gamma$)

A form of high-energy electromagnetic radiation with neutral charge, similar to X-rays.

Gold Foil Experiment

A 1910 experiment performed by Ernest Rutherford that established the existence of a small, dense, positively charged atomic nucleus based on alpha particle scattering.

Nucleus

The small, dense, positively charged core at the center of an atom that contains protons and neutrons and holds most of the atom's mass.

Proton

A positively charged subatomic particle located within the nucleus of an atom.

Isotope

Atoms of the same element that contain the same number of protons but differ in mass due to a different number of neutrons. Concept identified by Frederick Soddy.

Neutron

An uncharged subatomic particle in the nucleus with a mass approximately equal to a proton, discovered by James Chadwick in 1932.

Atomic Mass Unit (amu)

A unit of mass equal to $1.6605 \times 10^{-24}\text{ g}$, defined such that a carbon-12 atom weighs exactly $12\text{ amu}$.

Fundamental Unit of Charge ($e$)

The magnitude of electric charge on an electron or proton, equal to $1.602 \times 10^{-19}\text{ C}$.

Atomic Number ($Z$)

The number of protons present in the nucleus of an atom.

Mass Number ($A$)

The total number of protons and neutrons contained within the nucleus of an atom.

Empirical Formula

A chemical formula that expresses the simplest whole-number ratio of the elements present in a compound.

Molecular Formula

A chemical formula indicating the actual number of atoms of each element present in a molecule of a compound.

Structural Formula

A formula displaying the explicit bonding arrangement of atoms within a molecule.

Allotropes

Different structural forms of the same element in the same physical state, such as dioxygen ($O_2$) and ozone ($O_3$).

Cation

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

Anion

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

Ionic Hydrate

An ionic compound that contains a specific number of water molecules bound within its crystalline structure.

Formula Mass

The sum of the average atomic masses of all atoms present in a substance's chemical formula.

Molecular Mass

The formula mass specifically applied to covalent substances existing as discrete molecules.

Mole

The amount of a substance containing the same number of discrete entities as there are atoms in exactly $12\text{ g}$ of pure carbon-12.

Avogadro's Number ($N_A$)

The number of entities contained in one mole of a substance, equal to $6.022 \times 10^{23}$.

Molar Mass

The mass in grams of one mole of a substance, expressed in units of $\text{g}\text{ mol}^{-1}$.

Percent Composition

The percentage by mass of each element present in a chemical compound.

Solvent

The solution component present in a concentration significantly greater than all other components.

Solute

The solution component present at a much lower concentration than the solvent.

Aqueous Solution

A solution in which water serves as the solvent.

Molarity ($M$)

A concentration unit defined as the number of moles of solute dissolved in exactly one liter of solution ($\text{mol solute} / \text{L solution}$).

Dilution

The process of lessening a solution's concentration by adding more solvent, described by the relation $C_1V_1 = C_2V_2$.

Balanced Chemical Equation

A symbolic representation of a chemical change that uses equal numbers of each atom type on both reactant and product sides.

Complete Ionic Equation

A chemical equation explicitly representing all dissolved, dissociated ions in an aqueous reaction.

Net Ionic Equation

A chemical equation formed by removing spectator ions from a complete ionic equation, leaving only the species undergoing chemical change.

Spectator Ion

An ion present in solution that undergoes no chemical change and appears identical on both sides of a complete ionic equation.

Precipitation Reaction

A reaction in aqueous solution where dissolved species combine to form an insoluble solid product called a precipitate.

Solubility

The maximum concentration of a substance that can be dissolved in a given solvent under specified conditions.

Acid

A substance that dissolves in water to produce hydronium ions ($H_3O^+$).

Base

A substance that dissolves in water to yield hydroxide ions ($OH^-$).

Neutralization Reaction

A specific acid-base reaction between an acid and a base producing a salt and water.

Oxidation-Reduction (Redox) Reaction

A reaction in which one or more elements undergo a change in oxidation number due to electron transfer or shift.

Oxidation

The loss of electrons or an increase in oxidation number during a chemical reaction.

Reduction

The gain of electrons or a decrease in oxidation number during a chemical reaction.

Reducing Agent

The reactant species in a redox reaction that loses electrons, causing another species to be reduced while becoming oxidized itself.

Oxidizing Agent

The reactant species in a redox reaction that gains electrons, causing another species to be oxidized while becoming reduced itself.

Combustion Reaction

A redox reaction in which a fuel reacts rapidly with an oxidant such as oxygen gas.

Single-Displacement Reaction

A redox reaction in which an element or ion in a compound is replaced or displaced by another species.

Stoichiometry

The quantitative relationships between the amounts of reactants consumed and products formed in a balanced chemical reaction.

Limiting Reagent

The reactant that is completely consumed first in a chemical reaction, determining the maximum quantity of product that can form.

Theoretical Yield

The calculated mass of product expected to form from a given quantity of limiting reactant according to stoichiometry.

Actual Yield

The mass of product physically obtained from performing a chemical reaction in practice.

Percent Yield

A metric measuring reaction efficiency calculated as $\frac{\text{actual yield}}{\text{theoretical yield}} \times 100$.