Atomic Structure, Isotopes, and Average Atomic Mass

Vocabulary flashcards covering atomic structure, mass numbers, atomic numbers, isotope notations, subatomic composition calculations, and weighted average atomic mass from lecture notes.

Atomic Number ($Z$)

The number of protons in every atom of an element, which uniquely determines which element it is. In a neutral atom, it equals the number of electrons. It is displayed as a whole number above the element symbol on the periodic table.

Mass Number ($A$)

The total number of protons and neutrons in the nucleus of an atom. It applies to single individual atoms only and does not appear on the periodic table.

Neutron Calculation Formula

The mathematical relationship used to determine the number of neutrons in an atomic nucleus: $\text{Number of Neutrons} = \text{Mass Number} - \text{Atomic Number}$.

Isotopes

Atoms of the same element that have the same atomic number (same number of protons) but different numbers of neutrons and different mass numbers. They exhibit the same behavior in chemical reactions.

Element Symbol Notation

A standardized notation where the chemical symbol of an element is preceded by the mass number as a superscript and the atomic number as a subscript (e.g., ${}_{12}^{24}\text{Mg}$ or ${}_{78}^{195}\text{Pt}$).

Hyphen Notation

A notation method for isotopes consisting of the element's name followed by a hyphen and its mass number (e.g., platinum-195 or cobalt-60).

Atomic Mass Unit (amu)

A unit of mass defined as exactly $\frac{1}{12}$ of the mass of a carbon-12 atom, approximately equal to the mass of a single proton or neutron.

Average Atomic Mass

The weighted average of the atomic masses of all naturally occurring isotopes of an element, represented as a decimal number on the periodic table.

Weighted Average Formula for Atomic Mass

The equation used to calculate average atomic mass: $\text{Average Atomic Mass} = \frac{(\text{percent of isotope 1} \times \text{mass of 1}) + (\text{percent of isotope 2} \times \text{mass of 2}) + \text{\textellipsis}}{100}$.

Hydrogen-1 (${}_{1}^{1}\text{H}$)

The most abundant isotope of hydrogen (approximately $98.9\%$ to $99\%$ natural abundance), consisting of 1 proton and 0 neutrons.

Hydrogen-2 (${}_{1}^{2}\text{H}$)

An isotope of hydrogen with a natural abundance of $< 2\%$, consisting of 1 proton and 1 neutron.

Hydrogen-3 (${}_{1}^{3}\text{H}$)

A trace isotope of hydrogen consisting of 1 proton and 2 neutrons.

Hydrogen Isotopes Diagram

Visual representations of hydrogen-1 (${}_{1}^{1}\text{H}$), hydrogen-2 (${}_{1}^{2}\text{H}$), and hydrogen-3 (${}_{1}^{3}\text{H}$), showing nuclei containing 1 proton with 0, 1, and 2 neutrons, respectively.

Chlorine-37 (${}_{17}^{37}\text{Cl}$) Subatomic Composition

An isotope of chlorine with atomic number $17$ and mass number $37$, consisting of $17$ protons, $20$ neutrons, and $17$ electrons.

Platinum-195 (${}_{78}^{195}\text{Pt}$) Subatomic Composition

An isotope of platinum with atomic number $78$ and mass number $195$, consisting of $78$ protons, $117$ neutrons, and $78$ electrons.

Phosphorus Isotopes (${}_{15}^{31}\text{P}$ and ${}_{15}^{32}\text{P}$)

Two isotopes of phosphorus both having atomic number $15$ ($15$ protons and $15$ electrons), with mass numbers $31$ ($16$ neutrons) and $32$ ($17$ neutrons).

Cobalt-60 (${}_{27}^{60}\text{Co}$) Subatomic Composition

An isotope of cobalt with atomic number $27$ and mass number $60$, consisting of $27$ protons, $33$ neutrons, and $27$ electrons.