Chemistry: Classification of Matter, Atomic Theory, and Periodic Trends (Vocabulary)

Vocabulary flashcards covering key terms and definitions from the notes on matter, atomic theory, light and quantum concepts, and the periodic table.

Matter

Anything that has mass and occupies space; classified by state (solid, liquid, gas) and composition.

States of Matter

The three common states: solid, liquid, and gas.

Solid

State with fixed shape and volume; particles vibrate in place.

Liquid

State with fixed volume that takes the shape of its container; flows.

Gas

State with no fixed shape or volume; expands to fill container.

Element

A substance that cannot be chemically broken down into simpler substances; defined by its atoms.

Atom

The smallest unit of an element that retains its chemical properties.

Molecule

A particle composed of two or more atoms bonded together.

Diatomic element

An element that naturally exists as a molecule of two atoms (e.g., H2, N2, O2, F2, Cl2, Br2, I2).

Compound

Substance composed of two or more elements in definite proportions with properties different from its elements.

Mixture

A substance composed of two or more particles that retain their own properties.

Heterogeneous mixture

Mixture with particles not evenly distributed (e.g., soda with ice, tea leaves in water).

Homogeneous mixture

Mixture with particles evenly distributed (e.g., air, salt in water, vodka).

Hypothesis

A tentative explanation of observations tested by controlled experiments.

Scientific law

A brief statement summarizing past observations and predicting future ones (describes what happens).

Theory

A model for how nature works that explains why or how something happens.

Law of Conservation of Mass

Mass cannot be created or destroyed in a chemical reaction; total mass before equals total mass after.

Law of Definite Proportions

All samples of a given compound have the same proportions of constituent elements by mass.

Law of Multiple Proportions

When two elements form two different compounds, the masses of element B that combine with 1 g of element A form a ratio of small whole numbers.

Dalton’s Atomic Theory

Postulates: elements are made of atoms; all atoms of an element are identical; compounds form from simple whole-number ratios; atoms cannot change into another element.

Electron

Negatively charged subatomic particle; fundamental to atomic structure.

Cathode ray

Beam of electrons produced in a cathode-ray tube, used to study electrons.

Charge-to-mass ratio

The ratio of electric charge to mass (e/m) for the electron.

Millikan’s Oil Drop Experiment

Experiment that measured the elementary charge by observing charged oil droplets in an electric field.

Rutherford’s Gold Foil Experiment

Experiment showing atoms have a dense, small nucleus; most of the atom is empty space.

Nucleus

Dense center of an atom that contains protons (and neutrons).

Atomic Number (Z)

Number of protons; defines the element.

Mass Number (A)

Total number of protons and neutrons in the nucleus.

Isotopes

Atoms of the same element with the same number of protons but different numbers of neutrons.

Ions

Atoms that gain or lose electrons and therefore carry a charge.

Cations

Positively charged ions formed when atoms lose electrons.

Anions

Negatively charged ions formed when atoms gain electrons.

Avogadro’s number

6.022 × 10^23; number of particles in one mole.

Mole

Amount of substance containing Avogadro’s number of entities.

Molar mass

Mass of one mole of a substance in g/mol; numerically equal to atomic/formula mass (amu).

Atomic mass unit (amu)

Unit for atomic/molecular masses; 1 amu = 1/12 mass of a C-12 atom.

Wave-particle duality

Concept that light and matter exhibit both wave-like and particle-like properties.

Frequency

Number of waves passing a point per second (ν).

Wavelength

Distance between successive crests of a wave (λ).

Speed of light

Constant c ≈ 3.00 × 10^8 m/s; speed of electromagnetic waves in vacuum.

EM spectrum

Range of electromagnetic radiation categorized by wavelength/frequency.

Interference

Combination of waves that can be constructive or destructive.

Diffraction

Bending or spreading of waves around obstacles or through openings.

Photoelectric effect

Emission of electrons from a material when light with sufficient energy shines on it.

Threshold frequency

Minimum frequency of light required to observe the photoelectric effect.

Bohr model

Early atomic model with electrons in fixed orbits around the nucleus.

Energy level

Discrete levels of energy for electrons in an atom; transitions emit/absorb photons.

Quantum numbers

Set (n, l, ml, ms) that describe electron properties in atoms.

Subshell

Subdivision of a shell defined by the angular momentum quantum number (s, p, d, f).

Electron configuration

Arrangement of electrons in subshells and orbitals for an atom.

Aufbau principle

Electrons fill the lowest-energy orbitals first.

Pauli Exclusion Principle

No two electrons in an atom can have the same four quantum numbers.

Hund’s Rule

Degenerate orbitals are filled singly with parallel spins before pairing.

Noble gas core

Short-hand electron configuration using the preceding noble gas.

Valence electrons

Electrons in the outermost shell, crucial for bonding.

Core electrons

Electrons in inner shells not typically involved in bonding.

Main-group elements

Elements in the s and p blocks of the periodic table.

Alkali metals

Group 1A metals; tend to lose one electron to attain noble gas configuration.

Halogens

Group 7A nonmetals; tend to gain one electron to form anions or share electrons.

Ion charges (predictable)

Periodically predictable charges for main-group elements based on group number.