Chapter 5 Atomic Theory: The Nuclear Model of the Atom

Vocabulary flashcards covering Dalton's theory, subatomic particles, isotopes, atomic mass concepts, and periodic table terminology from the notes.

Dalton's Atomic Theory

All matter is composed of atoms; atoms are indivisible; atoms of the same element are identical; atoms of different elements differ; atoms combine to form compounds.

Atom

The basic unit of an element; in Dalton's theory, considered indivisible.

Indivisible

A foundational idea in Dalton's theory that atoms cannot be broken into smaller particles.

Proton (p or p+)

Positively charged subatomic particle inside the nucleus; symbol p; mass is small compared to the nucleus; discovered by Rutherford.

Neutron (n or n0)

Electrically neutral subatomic particle in the nucleus; mass ~ equal to a proton; symbol n; discovered by James Chadwick.

Electron (e-)

Negatively charged subatomic particle outside the nucleus; symbol e-; mass ~1/1837 of a proton; discovered by J.J. Thomson.

Nucleus

Dense center of the atom containing protons and neutrons; contains most of the atom's mass; atom is mostly empty space.

Mass number (A)

Total number of protons and neutrons in the nucleus; A = Z + N.

Atomic number (Z)

Number of protons in the nucleus; identifies the element and determines its position on the periodic table.

Isotopes

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

Atomic mass unit (u)

1/12 the mass of a carbon-12 atom; standard unit for atomic masses.

Atomic mass

Weighted average mass of all isotopes of an element in a sample, accounting for isotope abundances.

Plum Pudding Model

Thomson's early model of the atom with electrons embedded in a positively charged sphere; atom is neutral and has internal structure.

Rutherford's Nuclear Model

Atom has a small, dense nucleus containing protons (and neutrons); electrons orbit; most of the atom is empty space.

Mass spectrum

Plot of isotope abundances versus mass-to-charge ratio (m/z); used to determine isotopic composition.

Mass-to-charge ratio (m/z)

Ratio of an ion's mass to its electric charge; in simple cases equals the isotope's mass in atomic mass units.

Nuclear symbol

Isotope notation showing mass number A, atomic number Z, and element X (A/Z X or name–mass number).

A = Z + N

Equation relating mass number A to atomic number Z and number of neutrons N.

Periodic Table

Organization of elements by increasing atomic number, showing recurring properties in groups and periods.

Period

Horizontal rows in the periodic table; vary in length.

Group

Vertical columns in the periodic table; elements with similar properties occupy the same group.

Main group elements (A)

Elements from groups 1, 2, and 13–18; also called representative elements.

Transition elements (B)

Elements in groups 3–12; transition metals.

Metals

Elements left of the stair-step line; typically good conductors, malleable, and ductile.

Nonmetals

Elements right of the stair-step line; typically poor conductors and brittle.

Metalloids

Elements bordering the stair-step line; exhibit mixed properties of metals and nonmetals.

Stair-step line

Diagonal line on the periodic table separating metals from nonmetals.

Lanthanoids

The 14 elements in the lanthanide series, part of the f-block of the periodic table.

Actinides

The 14 elements in the actinide series, part of the f-block of the periodic table.

Abundance

Proportion of a particular isotope found in a natural sample.