Atomic Theory Chapter 1-3

Chemical reaction

The transformation of a substance or substances into one or more new substances.

Law of conservation of mass

Mass is neither created nor destroyed during ordinary chemical reactions or physical changes.

Law of definite proportions

A chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound.

Law of multiple proportions

If two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers.

Dalton's Atomic Theory

A theory proposed by John Dalton states that all matter is composed of extremely small particles called atoms that are identical within the same element and cannot be subdivided, created, or destroyed.

Atom

The smallest particle of an element that retains the chemical properties of that element.

Nucleus

A very small region located at the center of an atom.

Proton

Particles with a positive charge in the nucleus.

Neutron

Particles with neutral electrical charge in the nucleus.

Electron

Negatively charged particles that surround the nucleus.

Subatomic particles

Neutrons, protons, and electrons.

Discovery of the Electron

The realization that cathode rays were composed of electrons, determined through experiments by Joseph John Thomson and Robert A. Millikan.

Discovery of the Atomic Nucleus

The discovery of a densely packed bundle of matter with a positive electric charge in the gold foil experiment by Ernest Rutherford, Hans Geiger, and Ernest Marsden.

Isotopes

Atoms of the same element that have different masses and different numbers of neutrons.

Average atomic mass

The weighted average of the atomic masses of the naturally occurring isotopes of an element.

Mole

The SI unit of the amount of substance that contains as many particles as the atoms.

Modern Atomic Theory

Theory that states atoms are divisible into smaller particles and a given element can have atoms with different masses

Nuclear forces

The short-range proton-neutron, proton-proton, and neutron-neutron forces that hold the nucleus particles together.

Radius of an atom

The distance from the center of the nucleus to the outer portion of its electron cloud.

Picometer

A unit that is more c

Atomic number

The number of protons of each atom of that element.

Mass number

The total number of protons and neutrons that make up the nucleus of an isotope.

Hyphen notation

Notation in which the mass number is written with a hyphen after the name of the element.

Nuclear symbol

The superscript indicates the mass number and the subscript indicates the atomic number.

Nuclide

A general term for a specific isotope of an element.

Avogadro’s number

Can be used to find the number of atoms of an element from the amount in mola or to find the amount of an element in moles from the number of atoms.

Molar mass

The mass of one mole of a pure substance.