Study Guide for Unit 3 Test: From Atoms to Reactions

Comprehensive vocabulary flashcards reviewing atomic structure, chemical formulas, stability, chemical reactions, and experimental design for the 8th Grade Science Unit 3 Test.

Atom

A fundamental unit of matter made of protons ($+$), neutrons (neutral), and electrons ($-$).

Proton

A positively charged ($+$) particle located within an atom; the number of protons equals the atomic number.

Neutron

A neutral subatomic particle that makes up an atom along with protons and electrons.

Electron

A negatively charged ($-$) particle arranged in energy levels (shells) around an atom.

Atomic Number

The number of protons in an atom, which also equals the number of electrons in a neutral atom.

Mass Number

The total number of protons $+$ neutrons in an atom.

Valence Electron

An electron located in the outer energy level (shell) of an atom that determines its reactivity.

Electron Configuration

The written arrangement showing how electrons are organized into energy levels (shells) for an atom.

Lewis Dot Structure

A diagram drawn to show the valence electrons of an atom.

Noble Gases

Elements that possess full outer shells and therefore usually do not react.

Compound

A substance formed when $2$ or more atoms join to become stable, occurring when electrons are transferred between atoms.

Bond

An interaction formed when electrons are transferred between atoms to achieve stability.

Charge

An electrical property of ions that must balance and cancel out to determine compound formulas.

Formula

The chemical representation of a compound, determined by balancing positive and negative charges using the least common multiple.

Stability

The state an atom achieves when it has a full outer shell by gaining, losing, or sharing electrons.

Valence Shell

The outermost electron energy level or shell of an atom.

Reactive

The tendency of atoms with incomplete outer shells to readily gain, lose, or share electrons.

Chemical Reaction

A process that produces new substances.

Evidence (of a Reaction)

Observable indications that a chemical reaction has occurred, including gas production, temperature change, color change, formation of a precipitate, or odor change.

Reaction Rate

The speed at which a chemical reaction occurs, which can be affected by temperature and the size of molecules or compounds.

Variables

Factors that can change in an experiment.

Independent Variable

A factor that is intentionally manipulated or changed by the experimenter in an experiment.

Dependent Variable

A factor that changes in response to the independent variable and is measured in an experiment.

Control

A standard or group in an experiment kept without the experimental treatment to provide a baseline for comparison.