Atoms, Subatomic Particles, Isotopes & Atomic Models

Flashcards covering basic chemistry concepts including subatomic particles, atomic notation, the classification of isotopes, isobars, and isotones, and the historical development of atomic models.

Matter

Anything that has mass and occupies space.

Atom

The smallest unit of an element that retains the chemical identity or properties of that element.

Subatomic particles

Particles smaller than an atom, specifically protons, neutrons, and electrons.

Nucleus

The dense central region of an atom containing protons and neutrons.

Electron region

The area around the nucleus, described in modern chemistry as orbitals or electron clouds, where electrons are found.

Proton

A subatomic particle located in the nucleus with a charge of $+1$ and a relative mass of approximately $1\,amu$.

Neutron

A subatomic particle located in the nucleus with a charge of $0$ and a relative mass of approximately $1\,amu$.

Electron

A negative subatomic particle located outside the nucleus with a charge of $-1$ and a relative mass approximately $1/1836$ of a proton.

Atomic number ($Z$)

The number of protons in an atom's nucleus, which identifies the element and determines the rule $Z = p$.

Mass number ($A$)

The total number of protons plus neutrons in a single atom or isotope, calculated by the formula $A = p + n$.

Ion

An atom or molecule where the electron number is not equal to the proton number; a positive ion has lost electrons, while a negative ion has gained electrons.

Isotopes

Atoms of the same element with the same atomic number (protons) but different numbers of neutrons and therefore different mass numbers.

Isobars

Atoms of different elements that have the same mass number ($A$) but different atomic numbers ($Z$).

Isotones

Atoms of different elements that have the same number of neutrons.

Iodine-131

A radioactive iodine isotope used in thyroid-related diagnosis and treatment.

Carbon-14

A radioactive carbon isotope used in radiocarbon dating to estimate the age of fossils and archaeological materials.

Atomic mass unit ($amu$ or $u$)

A unit for atomic-scale masses where one carbon-12 atom is assigned a mass of exactly $12\,u$.

Atomic mass (Weighted average)

The sum of each isotope's mass multiplied by its fractional abundance, representing the average mass of an element's naturally occurring isotopes.

Law of conservation of mass

The principle that in ordinary chemical reactions, atoms are rearranged but are not created or destroyed.

Solid-sphere model

The early atomic model proposed by John Dalton where the atom is represented as a tiny, solid, indivisible sphere.

Plum-pudding model

The model proposed by J. J. Thomson featuring negative electrons embedded in a diffuse positive region.

Nuclear model

The model proposed by Ernest Rutherford following the gold-foil experiment, describing the atom as mostly empty space with a tiny, dense, positively charged nucleus.

Planetary / energy-level model

The model proposed by Niels Bohr where electrons occupy specific quantized energy levels around the nucleus.

Quantum-mechanical model

The modern model associated with Erwin Schrödinger where electrons are described by orbitals or probability distributions rather than fixed fixed paths.

s orbital

A spherical-shaped orbital region that can hold a maximum of $2$ electrons.

p orbital

A dumbbell-like orbital region that can hold a maximum of $6$ electrons.

d orbital

A complex, multi-lobed orbital region that can hold a maximum of $10$ electrons.

f orbital

A highly complex orbital region that can hold a maximum of $14$ electrons.