Honors Chemistry Unit 1 Reading 1: Structure of the Atom & Nuclear Chemistry - Vocabulary

Vocabulary flashcards covering key terms from the notes on atomic structure, isotopes, ions, atomic theory, historical experiments, Bohr model, periodic table, and radioactivity.

Atom

The smallest particle of an element that retains the properties of that element; composed of protons, neutrons, and electrons.

Proton

Positively charged subatomic particle located in the nucleus.

Neutron

Electrically neutral subatomic particle located in the nucleus.

Electron

Negatively charged subatomic particle located outside the nucleus in energy levels.

Nucleus

Center of the atom that contains protons and neutrons; accounts for most of the atom's mass.

Atomic number (Z)

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

Mass number (A)

Total number of protons and neutrons in a given atom or isotope.

Isotopes

Atoms of the same element with the same number of protons but different numbers of neutrons; different mass numbers but similar chemical behavior.

Ion

Atom with a net electrical charge due to loss or gain of electrons.

Cation

Positively charged ion formed when electrons are lost.

Anion

Negatively charged ion formed when electrons are gained.

AZ notation

Notation with mass number (A) on top and atomic number (Z) on the bottom next to the symbol, e.g., for an isotope.

Mass number vs Atomic mass

Mass number is protons plus neutrons (an integer) for a single atom; atomic mass is a weighted average of all isotopes (amu, a decimal).

Atomic mass unit (amu)

Unit used for atomic masses; the weighted average mass of isotopes; reported with decimal values.

Average atomic mass

Weighted average of isotopes based on their abundances; abundances sum to 1.00; units in amu.

Isotope abundances

Relative amounts of each isotope in a naturally occurring element; must sum to 1.00.

Dalton's atomic theory

Early 1800s theory that matter is made of indivisible atoms; atoms of an element are identical; atoms combine in whole-number ratios.

Law of Conservation of Mass

In chemical reactions, atoms are rearranged but not created or destroyed.

Law of Definite Proportions

A given compound always contains the same elements in fixed mass ratios.

J. J. Thomson

Discovered the electron using the cathode ray tube; proposed the plum pudding model.

Electron

Subatomic particle with negative charge; fundamental component of atoms.

Plum pudding model

Early atomic model where a positively charged sphere contained electrons embedded like raisins in pudding.

Robert Millikan

Measured the charge of the electron with the oil drop experiment.

Ernest Rutherford

Gold foil experiment; discovered the dense positively charged nucleus; atoms are mostly empty space.

Nucleus (nuclear model)

Dense center of the atom containing protons and neutrons; electrons orbit outside.

Niels Bohr

Explained hydrogen line spectra by proposing electrons occupy discrete energy levels.

Hydrogen line spectrum

Hydrogen emits light at specific wavelengths when electrons transition between energy levels.

Bohr energy levels

Electron shells with capacities: 1st level 2, 2nd level 8, 3rd level 18, 4th level 32.

Octet rule

Atoms tend to have eight electrons in their outermost shell; metals lose electrons, nonmetals gain electrons.

Valence electrons

Electrons in the outermost shell that determine chemical properties.

Fission

Splitting of a large nucleus into smaller nuclei, releasing energy (e.g., in nuclear reactors).

Fusion

Combining of light nuclei to form a larger nucleus, releasing energy; powers stars; requires extreme conditions.

Half-life

The time required for half of a radioactive sample to decay.

Radioactivity

Emission of radiation from unstable nuclei as they decay toward stability.

Moseley

Showed elements should be arranged by increasing atomic number, not mass.

Mendeleev

Created the early periodic table and predicted properties of undiscovered elements.

Chlorine valence and Cl- formation

Chlorine has 7 valence electrons and gains one electron to form Cl-.