Chemistry Lecture Notes: Matter, Measurement, and the Periodic Table

Vocabulary flashcards covering key terms, definitions, and concepts from the chemistry notes.

Chemistry

An experimental and theoretical science that seeks to understand matter by studying the behavior of atoms, molecules, and their transformations.

Atom

A submicroscopic particle that is the fundamental building block of ordinary matter.

Molecule

Two or more atoms bonded together in a specific geometrical arrangement; attachments are called bonds.

Bond

A force that holds atoms together in a molecule; bonds vary in type and strength.

Observation

The act of noticing and recording information about the natural world; the first step in the scientific method.

Hypothesis

A tentative explanation to explain observations that can be tested by experiments.

Qualitative data

Descriptive data that do not involve numbers.

Quantitative data

Numeric data obtained from measurements.

Law (in science)

A statement that summarizes a large number of experiments and observations.

Theory

A unifying principle that explains a body of facts and supported laws; may be revised or disproved with new evidence.

Oxygen (O2)

Diatomic oxygen gas composed of two oxygen atoms; essential for respiration; colorless and odorless.

Ozone (O3)

Triatomic oxygen; bluish gas with a pungent smell that protects the earth from UV rays; not required for respiration.

Matter

Anything that has mass and occupies space.

State of matter

Solid, liquid, or gas.

Pure substance

Matter with a fixed composition; either an element or a compound.

Mixture

Matter with variable composition made of two or more substances.

Element

A pure substance that cannot be decomposed by chemical reactions; composed of a single type of atom.

Compound

A pure substance that can be decomposed; made of molecules containing two or more different kinds of atoms.

Homogeneous mixture

A mixture with uniform composition throughout; its components are not easily distinguished.

Heterogeneous mixture

A mixture with nonuniform composition; different regions have different properties.

Density

Mass per unit volume; an intensive property that varies with temperature and pressure.

Archimedes’ principle

Volume of an irregular solid can be determined by water displacement.

Physical change

A change that alters the state or appearance without changing the substance’s composition.

Chemical change

A process that changes the composition of matter; atoms rearrange to form new substances.

Rusting

A chemical change in which iron reacts with oxygen to form iron oxide.

Combustion

Burning; a chemical reaction that typically produces heat and light.

Physical property

A property that can be observed or measured without changing the substance’s composition (e.g., color, density, melting point).

Chemical property

A property that describes how a substance behaves during a chemical change.

Measurement

Description of matter that includes a number and a unit.

Unit

A standard quantity used to describe measurements (e.g., meter, gram, liter).

SI units

The International System of Units used for scientific measurements.

prefixes (Giga, Mega, kilo, deci, centi, milli, micro, nano, pico)

Metric prefixes that multiply or divide units by powers of ten (e.g., kilo = 10^3, milli = 10^-3).

Temperature

Measure of the average kinetic energy of particle motion; measured in Kelvin, Celsius, or Fahrenheit.

Thermal equilibrium

When two objects reach the same temperature and no net heat flows between them.

Kelvin (K)

Absolute temperature scale; 0 K is absolute zero; temperature values are never negative.

Celsius (°C)

Temperature scale in which water freezes at 0°C and boils at 100°C at 1 atm.

Fahrenheit (°F)

Temperature scale primarily used in the U.S.; differences between °F and °C relate to conversion factors.

Density units

Solids: g/cm^3; Liquids: g/mL; Gases: g/L; 1 cm^3 = 1 mL.

Mass

A measure of the amount of matter in an object; used with density to calculate volume or mass.

Volume

The amount of space that a substance occupies; measured in mL, cm^3, L, etc.

Significant figures

Digits that carry meaning about the precision of a measurement; rules govern which digits are significant.

Exact numbers

Numbers known with complete certainty (counted values or defined relations) and have unlimited significant figures.

Rounding

Process of reducing the number of significant figures in a value, following established rules.

Dimensional analysis

Problem-solving method that uses conversion factors to relate different units and cancel unwanted units.

Conversion factor

A ratio that expresses how many of one unit are equal to another unit; can be exact or measured.

Conceptual plan

A visual outline showing the strategic route to solve a problem, focusing on units or equations.

Equivalence statement

A stated relationship between two units, e.g., 1 inch = 2.54 cm.

Dalton’s atomic theory

All matter is made of atoms; atoms of an element are identical; compounds form when atoms combine; chemical reactions rearrange atoms but do not create/destroy them.

Chemical formula

Notation showing the number and type of atoms in a molecule (e.g., C12H22O11).

Chemical equation

Expression showing reactants converting to products using formulas and symbols.

Element symbol

A one- or two-letter abbreviation for an element; first letter capitalized, second letter lowercase if present.

Periodic Table

A table organizing elements by atomic number, properties, and periodicity; groups (columns) and periods (rows) show patterns.

Group

A vertical column in the periodic table; elements in a group share similar properties.

Period

A horizontal row in the periodic table; elements in a period show a repeating pattern of properties.

Metals

Elements that are typically solid (except mercury), good conductors, ductile, and malleable.

Nonmetals

Elements that typically do not conduct electricity; exist in various states and include elements like oxygen and carbon.

Metalloids

Elements with properties between metals and nonmetals; semiconductors (e.g., B, Si, Ge, As, Sb, Te).

Allotropes

Different forms of the same element with different structures and properties (e.g., O2 vs O3; diamond vs graphite).

Different forms of elements that exist as molecules

Many nonmetals form molecules (e.g., H2, N2, O2, F2, Cl2; polyatomic examples include O3, P4, S8).