Unit 2: The Atom Study Guide

A complete set of 50 vocabulary flashcards covering atomic models, subatomic particles, ions, isotopes, periodic table organization, and nuclear processes from Unit 2.

John Dalton

Scientist who proposed the Solid Sphere / Billiard Ball model, stating that atoms are tiny solid spheres with no internal particles and that each element has its own type of atom.

Solid Sphere / Billiard Ball Model

The atomic model proposed by John Dalton that depicts atoms as tiny solid spheres without internal particles.

J. J. Thomson

Scientist who discovered the electron and proposed the Plum Pudding model consisting of negative electrons embedded in a positive sphere.

Plum Pudding Model

The atomic model proposed by J. J. Thomson featuring negative electrons embedded in a positive sphere, demonstrating that atoms contain smaller, negatively charged particles.

Ernest Rutherford

Scientist whose gold-foil experiment supported the Nuclear Model, showing that positive charge and most mass are concentrated in a tiny, dense nucleus and that the atom is mostly empty space.

Nuclear Model

The atomic model proposed by Ernest Rutherford stating that an atom is mostly empty space with its positive charge and most of its mass concentrated in a central nucleus.

Gold-Foil Experiment

The experiment conducted by Ernest Rutherford that supported the existence of a tiny, dense, positive nucleus and established that the atom is mostly empty space.

Niels Bohr

Scientist who proposed the Planetary / Bohr Model, establishing that electrons occupy specific energy levels (shells) around the nucleus.

Planetary / Bohr Model

The atomic model in which electrons occupy specific energy levels or shells around the nucleus rather than possessing arbitrary energies.

Erwin Schrödinger

Scientist who developed the Electron Cloud / Quantum Model, proposing that electrons are described by probability regions rather than fixed circular paths.

Electron Cloud / Quantum Model

The atomic model in which electrons are described by probability regions rather than fixed circular planetary orbits.

James Chadwick

Scientist who discovered the neutron, a neutral subatomic particle located in the nucleus alongside protons.

Model Order

The historical progression of atomic models: Dalton $\rightarrow$ Thomson $\rightarrow$ Rutherford $\rightarrow$ Bohr $\rightarrow$ Schrödinger, followed by Chadwick's discovery of the neutron.

Proton

A subatomic particle located in the nucleus with a charge of $+1$ and a relative mass of about $1\,\text{amu}$ that identifies the element and contributes to its mass.

Neutron

A subatomic particle located in the nucleus with a charge of $0$ and a relative mass of about $1\,\text{amu}$ that adds mass and helps stabilize the nucleus.

Electron

A subatomic particle located in the electron cloud with a charge of $-1$ and a very small relative mass compared to protons and neutrons, important in bonding and chemical behavior.

Nucleus

The tiny, dense, positive center of an atom containing protons and neutrons where most of the atom's mass is concentrated.

Electron Cloud

The space surrounding the nucleus occupied by electrons in probability regions.

Atomic Number

The number of protons in an atom, which uniquely identifies the element.

Mass Number

The total number of protons plus neutrons in a single atom.

Neutron Calculation Rule

The calculation shortcut used to find the number of neutrons in an atom: $\text{Neutrons} = \text{mass number} - \text{atomic number}$.

Neutral Atom

An atom that possesses no net electrical charge because the number of protons equals the number of electrons ($\text{protons} = \text{electrons}$).

Ion

An atom that has acquired a net electrical charge as a result of gaining or losing electrons.

Cation (Positive Ion)

An atom that has lost electrons, resulting in a net positive charge; its electron count equals protons minus the positive charge amount.

Anion (Negative Ion)

An atom that has gained electrons, resulting in a net negative charge; its electron count equals protons plus the negative charge magnitude.

Valence Electrons

Electrons residing in the outermost occupied energy level that strongly influence chemical bonding and reactions.

Isotope

Atoms of the same element that have the same number of protons (atomic number) but different numbers of neutrons (mass numbers).

Carbon-12

An isotope of carbon containing $6$ protons and $6$ neutrons.

Carbon-14

An isotope of carbon containing $6$ protons and $8$ neutrons.

Isotope Notation

A representation where the mass number is written at the upper left, the atomic number at the lower left, and the charge (if present) at the upper right of the element symbol.

Common Name Format (Isotopes)

A naming convention that identifies an isotope using the element name followed by a hyphen and the mass number, such as carbon-$14$.

Average Atomic Mass

The weighted average mass of an element's naturally occurring isotopes, calculated using the formula: $\text{Average atomic mass} = \Sigma (\text{isotope mass} \times \text{fractional abundance})$.

Fractional Abundance

The decimal representation of an isotope's natural abundance, obtained by dividing its percentage abundance by $100$.

Group

A vertical column on the periodic table that goes up and down.

Period

A horizontal row on the periodic table that goes across.

Metals

Elements located mostly on the left and center of the periodic table that are generally shiny, malleable, and good conductors of heat and electricity.

Nonmetals

Elements located mostly on the upper right of the periodic table (plus hydrogen) that are often poor conductors and can be brittle if solid.

Metalloids

Elements located near the staircase boundary between metals and nonmetals that exhibit mixed properties of both.

Alkali Metals

The family of very reactive metals located in Group $1$ of the periodic table (excluding hydrogen).

Alkaline Earth Metals

The family of reactive metals located in Group $2$ of the periodic table, generally less reactive than Group $1$ metals.

Halogens

The family of very reactive nonmetals located in Group $17$ that have $7$ valence electrons and often form $-1$ ions.

Noble Gases

The family of very unreactive elements located in Group $18$ whose outer energy levels are full (helium has $2$ electrons; others have $8$).

Transition Metals

The metallic elements located in the center block of the periodic table where simple group-to-valence-electron patterns are less reliable.

Group 13 Elements

Main-group elements (such as B and Al) that possess $3$ valence electrons.

Group 14 Elements

Main-group elements (such as C and Si) that possess $4$ valence electrons.

Group 15 Elements

Main-group elements (such as N and P) that possess $5$ valence electrons.

Group 16 Elements

Main-group elements (such as O and S) that possess $6$ valence electrons.

Fission

A nuclear process in which a large nucleus splits into smaller nuclei, which can release energy and neutrons and is used in nuclear power.

Fusion

A nuclear process in which small nuclei combine into a larger nucleus, releasing energy in stars such as the Sun.

Radioactive Decay

A spontaneous nuclear process in which an unstable nucleus emits particles and/or energy to change into a different nuclide or element.