Lecture Notes: Significant Figures, Atomic Structure, and the Periodic Table (Vocabulary)

A vocabulary set covering significant figures, atomic structure, and foundational chemistry concepts from the lecture notes.

Significant figures

Rules for determining how many digits in a measurement are meaningful and how to round results; includes nonzero digits, zeros between nonzero digits, leading zeros, trailing zeros with a decimal point; exact numbers are not counted.

Exact numbers

Counted quantities or defined quantities that do not limit the number of significant figures.

Atomic Number (Z)

The number of protons in an atom (and, for neutral atoms, the number of electrons); defines the element.

Mass Number (A)

Total number of protons and neutrons in the nucleus of an atom.

Proton

Positively charged subatomic particle located in the nucleus.

Electron

Negatively charged subatomic particle with negligible mass.

Neutron

Neutral subatomic particle with mass similar to a proton.

Alpha particle

Helium nucleus; positively charged; low intensity radiation.

Beta particle

High-energy electron; negatively charged particle.

Gamma ray

High-energy electromagnetic radiation; highly damaging to tissue.

Mendeleev (Periodic Table)

Father of the Periodic Table; arranged elements by increasing weight and left gaps for missing elements.

Periodic Table

Organization of elements showing periodic trends and properties; groups share similar properties.

Nonmetals

Elements lacking metallic properties; may be gases or dull solids.

Metalloids

Elements with intermediate properties between metals and nonmetals.

Metals

Elements with metallic luster, good conductors, usually solids, malleable and ductile.

Thomson's experiment

Experiment leading to the discovery of electrons and suggesting the existence of negatively charged particles.

Thomson's Plum Pudding model

Early atomic model depicting a positively charged 'soup' with embedded electrons.

Radioactivity

Emission of radiation from unstable nuclei; discovered by Marie Curie and others; led to discovery of new elements like radium and polonium.

Nitric oxide (NO)

NO; nitrogen oxide, biologically important signaling molecule.

Nitrogen dioxide (NO2)

NO2; nitrogen dioxide, a pollutant involved in photochemical smog.

Dinitrogen monoxide (N2O)

N2O; dinitrogen monoxide, commonly called laughing gas.

Dalton's Law of Multiple Proportions

Compounds may form from elements in more than one definite proportion, producing different compounds (e.g., NO, N2O, NO2).

Proust's Law of Definite Proportions

A given chemical compound will always contain its constituent elements in a fixed, definite proportion by mass (e.g., H2O).

Law of Conservation of Mass

Mass cannot be created or destroyed in a chemical reaction; total mass remains constant.

Relative atomic mass

Average mass of an atom relative to 1/12 the mass of a carbon-12 atom.

Aristotle

Ancient philosopher who proposed matter is continuous, a view later challenged by atomic theory.

Democritus

Ancient philosopher who coined 'atomos'—indivisible, microscopic particles—the idea of atoms.

Alchemy

Medieval precursor to chemistry; sought the Philosopher's Stone and transmutation of metals; not scientific by modern standards.

Philosopher's Stone

Legendary substance believed to turn base metals into gold.

Antoine Lavoisier

Father of Modern Chemistry; first to identify oxygen and formulate the Law of Conservation of Mass.

Oxygen (discovery)

Gas identified as essential for combustion; central to Lavoisier's experiments.