CHEM 107 Exam 1 Key Terms & Vocabulary

Vocabulary-style practice flashcards covering fundamental chemistry terms, historical atomic theory discoveries, subatomic particles, periodic groups, and chemical composition from CHEM 107 Chapters 1 through 3.

Matter

Anything that takes up space and has mass.

Element

A pure substance made of one kind of atom.

Compound

A pure substance made of two or more elements in a fixed, definite proportion.

Homogeneous mixture

A mixture that is uniform throughout, such as air or salt water.

Heterogeneous mixture

A nonuniform mixture in which different parts can be distinguished, such as muddy water or a chocolate-chip cookie.

Diatomic elements

Seven elements that exist naturally as paired-atom molecules: $H_2$, $N_2$, $O_2$, $F_2$, $Cl_2$, $Br_2$, and $I_2$.

Physical property

A characteristic that can be observed without changing a substance's identity, such as color, density, state, or melting/boiling point.

Chemical property

A property describing how a substance can react or change identity, such as flammability, corrosion, or reactivity.

Physical change

A change in which the identity of a substance stays the same and only its form or state changes.

Chemical change

A change in which one or more substances react to form new substances.

Extensive property

A property that depends on the amount of matter present, such as mass or volume.

Intensive property

A property that is independent of the amount of matter present, such as density, color, or boiling point.

Hypothesis

A tentative explanation for why something happens.

Scientific law

A statement that summarizes repeated observations and predicts what occurs.

Scientific theory

A well-established explanation or model for how or why something happens.

Law of Conservation of Matter

States that in a chemical reaction, matter is neither created nor destroyed.

Density

Mass per unit volume, defined by the formula $\text{density} = \frac{\text{mass}}{\text{volume}}$.

Accuracy

The closeness of a measurement to the accepted or true value.

Precision

The closeness of repeated measurements to one another.

Law of Definite Proportions

States that a given compound has the same elemental composition regardless of source.

Law of Multiple Proportions

States that the same elements can combine in different whole-number ratios to form different compounds.

J. J. Thomson

Scientist who performed cathode-ray experiments and discovered the electron.

R. A. Millikan

Scientist who performed the oil-drop experiment to determine the charge of an electron.

Ernest Rutherford

Scientist who performed the gold-foil experiment, discovered the small dense nucleus, and showed the atom is mostly empty space.

James Chadwick

Scientist who discovered the neutron.

Henri Becquerel

Scientist who discovered radioactivity.

Marie Curie

Scientist who studied radiation from unstable atoms and discovered radium and polonium.

Proton

A subatomic particle located in the nucleus with a $+1$ charge, an approximate mass of $\text{1}\text{ amu}$, and whose count defines the atomic number.

Neutron

A subatomic particle located in the nucleus with a neutral charge ($0$) and an approximate mass of $\text{1}\text{ amu}$ that alters an atom's mass number and isotope status.

Electron

A subatomic particle located outside the nucleus with a $-1$ charge and an approximate mass of $\text{0}\text{ amu}$ that affects ion charge.

Atomic number ($Z$)

The number of protons in an atom's nucleus.

Mass number ($A$)

The total number of protons plus neutrons in an atom.

Cation

A positively charged ion formed when an atom loses electrons.

Anion

A negatively charged ion formed when an atom gains electrons.

Isotopes

Atoms of the same element (same number of protons) with different numbers of neutrons and different masses.

Alkali metals

Group 1 elements on the periodic table that typically form $+1$ ions.

Alkaline-earth metals

Group 2 elements on the periodic table that typically form $+2$ ions.

Halogens

Group 17 elements on the periodic table that typically form $-1$ ions.

Noble gases

Group 18 elements on the periodic table that are stable and nonreactive.

Ionic compound

A compound composed usually of a metal and nonmetal or polyatomic ions, held together by electrostatic attraction between cations and anions.

Molecular compound

A compound composed of two or more nonmetals.

Molar mass

The sum of the atomic masses of every atom in a chemical formula, expressed with units of $g\,mol^{-1}$.

Avogadro's number

$6.022 \times 10^{23}$, representing the number of particles in one mole of a substance.

Empirical formula

A chemical formula showing the smallest whole-number ratio of atoms in a compound.

Molecular formula

A chemical formula showing the actual number of each type of atom in a compound.

Limiting reactant

The reactant in a chemical reaction that produces the smaller amount of product and runs out first.

Theoretical yield

The maximum amount of product predicted to form from the limiting reactant in a chemical reaction.