Chapter 2: Atoms, Molecules, and Ions

Vocabulary flashcards reviewing core atomic principles, subatomic structures, isotopes, periodic trends, molecular representations, and chemical nomenclature rules.

Dalton's Atomic Theory

A theory proposing that elements are composed of small indivisible particles called atoms, all atoms of a given element are identical, compounds consist of combined elements, and chemical reactions involve only the rearrangement of atoms.

Law of Constant Composition

A law stating that the relative kinds and numbers of atoms are constant for any given compound.

Law of Multiple Proportions

A law stating that when two elements react to form more than one compound, a fixed mass of one element reacts with masses of the second element in ratios of small whole numbers.

Cathode Ray Tube

A sealed tube device used to discover electrons by directing beams of negatively charged particles from a cathode to an anode.

Electron

A negatively charged subatomic particle residing outside the nucleus with a charge of $-1$ ($-1.602 \times 10^{-19}\,C$) and a mass of $5.486 \times 10^{-4}\,amu$ ($9.10 \times 10^{-28}\,g$).

Radioactivity

The spontaneous emission of radiation or energetic particles by an unstable atomic nucleus, discovered by Henri Becquerel and named by Marie Curie.

Alpha ($\alpha$) Particles

High-mass, positively charged radiation particles ($2+$) that undergo slight deflection toward negatively charged plates.

Beta ($\beta$) Particles

Low-mass, negatively charged radiation particles consisting of electrons that deflect strongly toward positively charged plates.

Gamma ($\gamma$) Rays

High-energy neutral radiation that carries no charge and undergoes no deflection in electric or magnetic fields.

Plum Pudding Model

An early atomic model proposed by J.J. Thomson featuring negative electrons embedded throughout a sphere of positive charge.

Rutherford's Gold Foil Experiment

An experiment shooting alpha particles at thin gold foil, demonstrating that atoms consist mostly of empty space with a tiny, dense, positively charged nucleus.

Nucleus

The small, dense center of an atom containing protons and neutrons, housing virtually all of the atom's mass.

Proton

A positively charged subatomic particle located in the nucleus with a charge of $+1$ ($+1.602 \times 10^{-19}\,C$) and a mass of $1.0073\,amu$.

Neutron

An uncharged subatomic particle located in the nucleus with a mass of $1.0087\,amu$, discovered by James Chadwick in 1932.

Angstrom ($\text{\AA}$)

A non-SI unit of length used to express atomic dimensions, where $1\,\text{\AA} = 10^{-10}\,m$.

Atomic Mass Unit (amu)

A unit of mass defined as $1\,amu = 1.66054 \times 10^{-24}\,g$, where carbon-12 ($^{12}C$) has a mass of exactly $12\,amu$.

Atomic Number ($Z$)

The number of protons in the nucleus of an atom, uniquely identifying the chemical element.

Mass Number ($A$)

The total number of protons plus neutrons contained within an atom's nucleus.

Isotopes

Atoms of the same element having identical atomic numbers (protons) but different mass numbers due to differing numbers of neutrons.

Average Atomic Mass

The weighted average mass of naturally occurring isotopes of an element, calculated using their masses and natural fractional abundances.

Periodic Table

A systematic chart arranging chemical elements in order of increasing atomic number, displaying recurring periodic properties.

Periods

The horizontal rows of elements on the periodic table.

Groups

The vertical columns of elements on the periodic table containing elements with similar chemical properties.

Alkali Metals

The soft, highly reactive metallic elements in Group 1A of the periodic table ($\text{Li}$, $\text{Na}$, $\text{K}$, $\text{Rb}$, $\text{Cs}$, $\text{Fr}$).

Alkaline Earth Metals

The metallic elements constituting Group 2A of the periodic table ($\text{Be}$, $\text{Mg}$, $\text{Ca}$, $\text{Sr}$, $\text{Ba}$, $\text{Ra}$).

Chalcogens

The elements comprising Group 6A of the periodic table ($\text{O}$, $\text{S}$, $\text{Se}$, $\text{Te}$, $\text{Po}$).

Halogens

The reactive nonmetal elements of Group 7A on the periodic table ($\text{F}$, $\text{Cl}$, $\text{Br}$, $\text{I}$, $\text{At}$).

Noble Gases

The unreactive nonmetal gases found in Group 8A of the periodic table ($\text{He}$, $\text{Ne}$, $\text{Ar}$, $\text{Kr}$, $\text{Xe}$, $\text{Rn}$).

Diatomic Molecule

A molecule consisting of exactly two bonded atoms, such as natural $\text{H}_2$, $\text{N}_2$, $\text{O}_2$, $\text{F}_2$, $\text{Cl}_2$, $\text{Br}_2$, and $\text{I}_2$.

Empirical Formula

A chemical formula showing the lowest whole-number ratio of atoms of each element in a compound.

Molecular Formula

A chemical formula giving the exact number of atoms of each element present in a molecule.

Cation

A positively charged ion formed when an atom or group of atoms loses one or more electrons.

Anion

A negatively charged ion formed when an atom or group of atoms gains one or more electrons.

Monoatomic Ion

An ion consisting of a single atom carrying a net charge, such as $\text{Na}^+$ or $\text{Cl}^-$.

Polyatomic Ion

An ion composed of two or more atoms covalently bonded together carrying an overall net charge, such as $\text{SO}_4^{2-}$ or $\text{NH}_4^+$.

Ionic Compound

A neutral compound consisting of cations and anions, typically formed between metals and nonmetals.

Molecular Compound

A compound composed of discrete molecules containing nonmetals bonded together.

Oxyanion

A polyatomic anion containing oxygen combined with another element, named with endings like -ate or -ite.

Acid

A substance that yields hydrogen ions ($\text{H}^+$) when dissolved in water.

Chemical Nomenclature

The systematic system of rules used for naming chemical substances.