Chapter 4: Atomic Structure

Vocabulary practice flashcards covering fundamental concepts of atomic structure, historical models, subatomic particles, isotopes, ions, and chemical laws.

Atom

The particle composing all elements; all atoms of the same element possess unique, identifying parts, combine with different elements to form compounds, and can never be changed into another element.

Democritus (460–370 BC)

A Greek philosopher who was the first to use the word "atom" and believed that atoms were indivisible and indestructible, though his ideas lacked scientific support.

Aristotle (384–322 BC)

A Greek philosopher who rejected the theory of atoms and proposed that all matter is composed of four core elements: fire, air, water, and earth.

Law of Conservation of Matter

A law formulated by Antoine Lavoisier stating that matter is not created or destroyed during a chemical reaction.

Law of Definite Proportions

A law proposed by Joseph Proust stating that a compound is always composed of the same elements in the exact same proportion by mass.

Law of Multiple Proportions

A law demonstrated by John Dalton stating that when two elements form more than one compound, they combine in a ratio of small whole numbers.

Dalton’s Atomic Theory

A theory asserting that all elements are composed of indivisible "solid sphere" atoms, all atoms of a given element are identical, atoms of different elements differ in mass, and different atoms combine in simple whole-number ratios to form compounds.

Subatomic Particles

The three component particles that make up divisible atoms: protons ($p^+$), neutrons ($n^0$), and electrons ($e^-$).

Electron

The first subatomic particle identified, discovered in 1897 by J.J. Thomson; designated by the symbol $e^-$, bearing a charge of $-1$, having a mass of approximately $\sim 0\,\text{amu}$, and occupying most of an atom's volume outside the nucleus.

Cathode-Ray Tube

A sealed tube filled with gas at very low pressure where high voltage causes electrons to travel as a ray from the cathode ($-$) to the anode ($+$), deflected by magnets and electrically charged plates.

Plum Pudding Model

J.J. Thomson’s atomic model (also referred to as the chocolate chip cookie model) proposing that an atom consists of negative electrons embedded inside a sphere of positive electrical charge.

Proton

A subatomic particle located in the nucleus of an atom with the symbol $p^+$, a charge of $+1$, and a mass of $1\,\text{amu}$.

Neutron

A subatomic particle located in the nucleus of an atom with the symbol $n^0$, a neutral charge of $0$, and a mass of $1\,\text{amu}$.

Gold Foil Experiment

An experiment conducted by Ernest Rutherford in 1911 in which alpha particles were aimed at a thin sheet of gold foil, revealing that atoms are mostly empty space with a dense, positively charged center.

Rutherford’s Nuclear Model

An atomic model stating that an atom is mostly empty space with a dense center called the nucleus, which contains most of the mass, holds the protons and neutrons, and carries a positive charge, while electrons surround the nucleus.

Atomic Number

The number of protons in an atom, which uniquely determines the element's identity, equals its nuclear charge, and is written as a subscript.

Nuclear Charge

The total amount of positive charge present in the nucleus of an atom, determined directly by its number of protons.

Mass Number ($A$)

The total count of protons plus neutrons ($A = Z + N$) in the nucleus of an atom, commonly represented as a superscript or written after the element's name.

Isotope Notation

A standardized chemical notation written as $^A_Z X$, where $X$ is the chemical symbol, $A$ is the mass number, and $Z$ is the atomic number.

Ion

An atom that carries a net electric charge formed when an atom gains or loses electrons during a chemical reaction, resulting in an unequal number of protons and electrons.

Cation

A positively charged ion formed by the loss of one or more electrons through an oxidation reaction.

Anion

A negatively charged ion formed by the gain of one or more electrons through a reduction reaction.

LEO says GER

A mnemonic used to remember oxidation and reduction: LEO stands for "Loss of Electrons is Oxidation," and GER stands for "Gain of Electrons is Reduction."

Isotopes

Naturally occurring atoms of the same element that have identical numbers of protons (same atomic number) but different numbers of neutrons, resulting in different mass numbers.

Average Atomic Mass

The weighted average mass of all naturally occurring isotopes of an element, expressed in atomic mass units ($\text{amu}$), calculated using each isotope's mass and percent abundance relative to $^{12}\text{C} = 12.000\,\text{amu}$.