Modeling Atoms 1.1

Atom

The smallest particle of an element that retains its identity in a chemical reaction.

Early Atomic Theory

The initial concept of atoms as indivisible units of matter, lacking experimental evidence and explanations for chemical behavior.

John Dalton

Scientist who proposed the first modern Atomic Theory in 1803, studying element combination ratios.

Dalton’s Postulates

Five foundational statements about atoms, including their indivisibility and the uniqueness of elements.

Subatomic Particles

Smaller particles that make up atoms, including electrons, protons, and neutrons.

Electron

A negatively charged subatomic particle discovered by J.J. Thomson in 1897.

Cathode Ray

A glowing beam produced in a vacuum tube, consisting of electrons, which can be deflected by magnetic fields.

Plum-Pudding Model

Thomson's atomic model suggesting electrons are distributed throughout a positively charged material.

Proton

A positively charged subatomic particle discovered by Eugen Goldstein in 1886.

Neutron

A subatomic particle with no charge, confirmed by James Chadwick in 1932.

Nucleus

The small, dense center of an atom containing protons and neutrons, proposed by Ernest Rutherford.

Nuclear Atom

Rutherford's revised atomic model, indicating that most of the atom is empty space with a dense nucleus.

Atomic Number

The number of protons in an atom's nucleus, defining the element.

Periodic Table

An arrangement of elements based on atomic number and repeating properties.

Chemical Symbols

One or two-letter representations of elements used in formulas and the periodic table.

Mass Number

The total number of protons and neutrons in an atom.

Isotopes

Atoms of the same element with different numbers of neutrons and mass numbers.

Average Atomic Mass

A weighted average of the masses of an element's isotopes, reflecting their natural abundance.

Cation

A positively charged ion with more protons than electrons.

Anion

A negatively charged ion with more electrons than protons.

Hyphen Notation

A way to represent isotopes using the element's name followed by the mass number (e.g., Carbon-12).

Nuclear Symbol

A representation of an atom using its chemical symbol, atomic number, and mass number.

Atomic Mass Unit (amu)

A unit of mass used to express atomic and molecular weights, defined relative to carbon-12.

Fraction Abundance

The percentage of a specific isotope in a naturally occurring sample, expressed as a decimal for calculations.