CHEM131 Fall 2025 - Chapter 1: Atoms

Flashcards covering early atomic theory, subatomic particles, atomic structure models, laws of chemical combination, and fundamental concepts like atomic number, mass, ions, isotopes, Avogadro's number, and molar mass.

John Dalton's Atomic Theory (1804)

Proposed that matter consists of indivisible atoms, atoms of the same element are identical, atoms combine in small whole-numbered ratios to form compounds, and chemistry involves the rearrangement of atoms.

Law of Conservation of Matter

States that matter can neither be created nor destroyed, eventually formulated as the Conservation of Mass-Energy by Einstein.

Law of Multiple Proportions

When an element combines with a different element to form multiple compounds, the ratio of the masses of one element to a fixed amount of the second element is a ratio of small whole numbers.

Law of Definite Proportions (1797)

States that the same compound will always be comprised of its constituent elements in the same proportion by mass.

Atoms

The elementary building blocks of matter.

Crooke's tube

An evacuated glass tube with metal electrodes used to generate a continuous beam called a cathode ray.

Cathode ray

A continuous beam generated between electrodes in an evacuated Crooke's tube when pressure is lowered and a voltage is applied.

Millikan's Oil Drop Experiment (1909)

An experiment that determined the charge of a single electron, measuring it as approximately 1.592 x 10^-19 C.

Thomson Plum Pudding Model (1904)

An atomic model proposing that atoms consist of negatively charged corpuscles (electrons) enclosed in a sphere of uniform positive electrification, making the atom electrically neutral.

Rutherford's Gold Foil Experiment (1911)

An experiment where alpha particles were fired at gold foil, leading to the discovery that atoms have a small, dense nucleus containing nearly all of the atom's mass.

Rutherford Model of the Atom

Describes an atom as having a small, dense nucleus (comprised of protons and neutrons) surrounded by much lighter electrons.

Nucleus

The central, dense core of an atom that contains protons and neutrons.

Proton (p+)

A subatomic particle found in the nucleus with a relative charge of +1 and a relative mass of approximately 1 amu.

Neutron (n or n°)

A subatomic particle found in the nucleus with a relative charge of 0 and a relative mass of approximately 1 amu.

Electron (e-)

A subatomic particle that orbits the nucleus with a relative charge of -1 and a very small relative mass (approximately 0 amu compared to protons/neutrons).

Atomic number (Z)

The number of protons in an atom's nucleus, which also equals the number of electrons in a neutral atom. Elements are ordered by this number on the Periodic Table.

Ion

An electrically charged atom.

Cation

A positively charged ion formed when an atom loses electrons.

Anion

A negatively charged ion formed when an atom gains electrons.

Mass Number (A)

The total number of protons (Z) and neutrons (N) in an atom's nucleus (A = Z + N).

Isotope Symbol (A Z X Q)

A notation representing an isotope, where A is the mass number, Z is the atomic number, X is the element symbol, and Q is the electric charge.

Atomic mass

A weighted average of the masses of all naturally occurring isotopes of an element, typically expressed in atomic mass units (amu).

Mass Spectrometry

An analytical technique used to separate ions based on their mass-to-charge ratio using electric and magnetic fields.

Avogadro's Number

The value 6.022 x 10^23 items/mol, representing the number of elementary entities in one mole of a substance. It is a reciprocal unit (mol^-1).

Molar Mass

The mass in grams of 1 mole of an element or a compound. For compounds, it is the sum of the atomic masses of all atoms in the compound, numerically equivalent to atomic mass in amu.