Exam 1 Chem

Atomic Number (Z)

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

Atomic Mass

The weighted average of the masses of an element's isotopes.

Period

Horizontal rows in the periodic table that indicate the number of electron shells.

Group (Family)

Vertical columns in the periodic table; elements in the same group share similar chemical properties due to the same number of valence electrons.

Metals

Elements that are generally good conductors of heat and electricity and typically form positive ions.

Nonmetals

Elements that are generally poor conductors of heat and electricity, often forming negative ions or covalent bonds.

Metalloids (Semimetals)

Elements with properties intermediate between metals and nonmetals, often acting as semiconductors.

Alkali Metals

Group 1 metals (e.g., Li, Na, K) that are highly reactive and typically form +1 ions.

Alkaline Earth Metals

Group 2 metals (e.g., Be, Mg, Ca) that are reactive and typically form +2 ions.

Halogens

Group 17 nonmetals (e.g., F, Cl, Br) that are highly reactive and typically form -1 ions.

Noble Gases

Group 18 elements (e.g., He, Ne, Ar) that are very unreactive due to a full outer electron shell.

Scientific Method

A systematic approach to inquiry that includes observation, question, hypothesis, experimentation, analysis, and conclusion.

Hypothesis

A testable prediction or explanation for an observation.

Physical Change

A change in form or appearance of a substance but not in its chemical composition.

Chemical Change (Chemical Reaction)

A change that results in the formation of a new substance with different chemical properties.

Pure Substance

A material with a uniform and definite composition, which can be an element or a compound.

Compound

A pure substance formed when two or more different elements are chemically bonded together.

Mixture

A combination of two or more substances that are not chemically bonded.

Homogeneous Mixture (Solution)

A mixture where components are uniformly distributed and appear as a single phase.

Heterogeneous Mixture

A mixture where components are not uniformly distributed and can be visibly distinguished.

Significant Figures

Digits in a number that carry meaningful information about its precision.

Isotopes

Atoms of the same element with different numbers of neutrons and different mass numbers.

Average Atomic Mass

The weighted average mass of all naturally occurring isotopes of an element.

Scientific Notation

A method of expressing very large or small numbers concisely, in the format M × 10^n.

Dimensional Analysis

A mathematical technique used to convert between units using conversion factors.

Analog Measurement

A type of measurement that requires reading a scale and estimating a value.

Mass Number

The total number of protons and neutrons in an atomic nucleus.

Charge (C)

The electrical charge of an ion, indicating whether it is a cation (positive) or anion (negative).