Ch.2: Atoms, Molecules & Ions — Vocabulary Flashcards

Vocabulary-style flashcards covering key terms from Chapter 2: Atoms, Molecules & Ions (structure, isotopes, mass, and early history).

Atomic structure

The arrangement of subatomic particles: nucleus (protons and neutrons) surrounded by electrons; determines the atomic number (Z) and mass number (A).

Atomic number (Z)

The number of protons in the nucleus; identifies the element and equals the number of electrons in a neutral atom.

Mass number (A)

The total number of protons and neutrons in the nucleus.

Atomic mass unit (amu)

A unit used to express atomic masses; defined as 1/12 the mass of a 12C atom. Atomic masses are often given in amu.

Electron

A negatively charged subatomic particle with a very small mass; located in the electron cloud surrounding the nucleus.

Proton

A positively charged subatomic particle in the nucleus; mass about 1 amu; number equals the atomic number in a neutral atom.

Neutron

An electrically neutral subatomic particle in the nucleus with a mass similar to a proton.

Nucleus

The dense, small center of the atom containing protons and neutrons, held together by the strong nuclear force.

Isotope

Atoms of the same element (same Z) that have different numbers of neutrons (different A).

Isotopic abundance

The relative amount of each isotope of an element found in nature.

Average atomic mass

The weighted average of the isotopic masses based on their natural abundances; shown on the periodic table.

Mass spectrometry

An analytical technique that ionizes atoms, deflects ions in a magnetic field, and separates them by mass-to-charge ratio to determine masses and abundances.

Mass-to-charge ratio (m/z)

The ratio of an ion’s mass to its charge; used to separate ions by mass in mass spectrometry.

Cathode ray tube

A device used in early experiments (Thomson) to study electrons; led to the discovery of electrons.

Thomson

Physicist who discovered electrons in atoms using cathode ray tubes and proposed the plum pudding model.

Plum pudding model

Early atomic model in which electrons are embedded in a diffuse, positively charged sphere.

Millikan

Scientist famous for the oil-drop experiment, which measured the elementary charge of the electron.

Electron charge

The magnitude of the charge on an electron: −1.60 × 10^−19 coulombs.

Rutherford gold foil experiment

Experiment showing most of the atom is empty space and that a tiny, dense, positively charged nucleus exists in the center.

Nuclear atom

Modern view of the atom with a dense nucleus containing protons and neutrons and electrons surrounding it.

Proton

Positively charged particle in the nucleus; discovered through early canal-ray experiments; mass ≈ 1 amu.

Chadwick (neutron discovery)

Experiment that revealed the neutron as a neutral particle in the nucleus, completing the basic nuclear composition.

Atomic symbol (A and Z in notation)

Notation that shows mass number A and atomic number Z (e.g., 12C has A=12 and Z=6); identity is determined by the number of protons.

Empirical vs molecular formula

Empirical formula gives the simplest whole-number ratio of elements; molecular formula shows the actual number of atoms of each element in a molecule.

Mole concept

An amount of substance containing Avogadro’s number (6.022 × 10^23) of entities; molar mass in g/mol equals the mass of one mole of a substance.

Chemical nomenclature

Systematic naming of chemical compounds (rules for ionic and molecular compounds).