8.25 Atomic Mass, Isotopes, and Ionic/Covalent Nomenclature

A set of practice flashcards covering atomic mass, isotopes, weighted averages, and ionic/covalent naming conventions, including polyatomic ions and acids.

What does the atomic number represent?

The number of protons in the nucleus (and, for a neutral atom, the number of electrons).

What is mass number?

The total number of protons and neutrons in the nucleus; an integer and does not reflect actual mass precisely.

How does atomic mass differ from mass number?

Atomic mass is a weighted average of isotopic masses based on natural abundance; mass number is simply the sum of protons and neutrons.

Are atomic masses whole numbers or decimals?

Decimals — atomic masses are weighted averages and include fractions.

What is meant by a weighted average in atomic mass calculations?

An average where each isotope’s mass is weighted by its natural abundance.

Where does the atomic mass on the periodic table come from?

From the weighted average of all naturally occurring isotopes of the element, accounting for abundance.

What does the sigma (Σ) symbol mean in the atomic mass calculation?

It signifies summation of all isotope contributions to the atomic mass.

How do you calculate atomic mass from isotopes and their abundances?

Atomic mass = sum of (fractional abundance as a decimal × isotope mass) for all isotopes.

Why is the weighted average atomic mass not simply the arithmetic mean of isotope masses?

Because isotopes occur in different natural abundances, the average must be weighted by those abundances.

Using copper with isotopes 63 (62.9396 amu, 69.17%) and 65 (64.9278 amu, 30.83%), what is the approximate atomic mass?

Approximately 63.55 amu, calculated as (0.6917×62.9396) + (0.3083×64.9278).

What is the Criss-Cross method used for in naming or formula writing?

A method to derive formulas by crossing the charges of ions to balance, then reducing to the smallest whole-number ratio.

What are the two main types of compounds by bonding that affect naming?

Ionic compounds (metal + nonmetal) and covalent compounds (two nonmetals).

What is a binary ionic compound?

A compound composed of one metal cation and one nonmetal anion.

Which metals tend to have fixed charges, requiring no Roman numeral in their names?

Group 1 (+1), Group 2 (+2); also aluminum (+3), zinc (+2), and silver (+1).

How do you name a binary ionic compound with a metal that has a variable charge?

Name the metal with a Roman numeral indicating its charge, followed by the nonmetal anion (e.g., copper(II) nitride).

How do you determine the metal’s charge in a binary ionic compound when the metal can vary in charge?

Use the nonmetal’s typical charge (from its group) to balance to neutral; the metal’s charge is then shown with a Roman numeral in the name.

What is ammonium and why is it special in naming salts?

Ammonium (NH4+) is the only polyatomic cation; most polyatomic ions are anions.

How do you name a covalent compound like CO or PCl3?

First element named as is; second element named with -ide and prefixes to show numbers (e.g., carbon monoxide, phosphorus trichloride).

How are binary acids named?

Binary acids use the hydro- prefix with the root of the nonmetal and -ic suffix (e.g., HF → hydrofluoric acid).

If the name is copper(II) nitride, what is the formula?

Cu3N2 (copper in the +2 oxidation state balances nitride N3− with three copper ions).

What is a quick check after writing a formula from a name using criss-cross?

Ensure subscripts are in the lowest whole-number ratio by reducing common factors.

What is the general rule for naming an ionic compound from its formula?

Name the cation (metal) first, then the anion (nonmetal or polyatomic name); for monoatomic anions, end with -ide; include Roman numerals for metals with variable charges.