Atomic Theory, Periodic Table Trends, and Ionic Compounds

Vocabulary study set covering atomic models, subatomic particles, atomic numbers, isotopes, groups on the periodic table, diatomic elements, and ionic compound formation.

Democritus's Model of the Atom

Proposed circa 400 BC that atoms are the smallest particles of an element, indivisible, and indestructible, derived from the Greek word "Atomos".

Dalton's Atomic Theory

Proposed in 1803 that atoms are tiny, indestructible particles of unique sizes for each element that combine in whole number ratios to form compounds, explaining the law of conservation of mass and the law of multiple proportions.

Thomson's "Plum Pudding" Model

Proposed in 1897 following the cathode ray experiment, asserting that negatively charged electrons are embedded within a sphere of equal positive charge.

Rutherford's Gold Foil Experiment

A 1911 experiment demonstrating that positively charged alpha particles mostly pass through gold foil with occasional deflections, proving that the atom is mostly empty space with a dense, positively charged nucleus.

Proton

A positively charged subatomic particle located in the nucleus with a mass of $1.67 \times 10^{-24}\,\text{g}$ that determines the identity of an atom.

Neutron

A neutral subatomic particle located in the nucleus with a mass of $1.67 \times 10^{-24}\,\text{g}$ that helps hold positively charged protons together in the nucleus.

Electron

A negatively charged subatomic particle surrounding the nucleus with a mass of $9.11 \times 10^{-28}\,\text{g}$.

Atomic Number ($Z$)

The total number of protons present in the nucleus of an atom.

Mass Number ($A$)

The total number of protons and neutrons in the nucleus of an atom.

Isotopes

Atoms of the same element that have the same atomic number ($Z$) but different mass numbers ($A$) due to differing numbers of neutrons.

Nuclear Symbol

A symbol written in the form $\text{}^{A}_{Z}\text{X}$ indicating the mass number ($A$), atomic number ($Z$), and element symbol ($\text{X}$) of a specific isotope.

Alkali Metals

Group 1 elements on the periodic table that exhibit metallic properties.

Alkaline Earth Metals

Group 2 elements on the periodic table.

Transition Metals

Elements belonging to Groups 3 through 12 on the periodic table that form cations with various positive charges.

Halogens

Elements belonging to Group 17 (or 7A) on the periodic table.

Noble Gases

Group 18 (or 8A) elements that naturally exist as individual unreactive atoms.

Metals

Elements located on the left side of the periodic table characterized as shiny, malleable, ductile, and good conductors of electricity and heat.

Non-metals

Elements located on the right side of the periodic table that lack metallic properties, vary widely in properties, and form negative ions (anions) by gaining electrons.

Metalloids

Elements located between metals and non-metals on the periodic table that share properties of both.

Diatomic Molecules

Seven elements that exist as two identical bonded atoms in their elemental forms: $\text{H}_2$, $\text{N}_2$, $\text{O}_2$, $\text{F}_2$, $\text{Cl}_2$, $\text{Br}_2$, and $\text{I}_2$.

Table 4.5: Diatomic Elements Properties

A table detailing the elemental states and molecular formulas at $25\,^{\circ}\text{C}$ for diatomic elements, including pale blue $\text{O}_2$ gas, pale yellow $\text{F}_2$ gas, pale green $\text{Cl}_2$ gas, reddish brown $\text{Br}_2$ liquid, and lustrous dark purple $\text{I}_2$ solid.

Cation

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

Anion

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

Ionic Bond

The strong force of attraction between oppositely charged cations and anions.

Ionic Compound Charge Balance

The principle that cations and anions combine in proportions resulting in a neutral compound with a net charge of $0$, such as one $\text{Mg}^{2+}$ cation balancing two $\text{Cl}^-$ anions to form $\text{MgCl}_2$.

Molecule

A group of atoms bonded together by chemical forces.

Compound

A substance composed of more than one type of element bonded together.