Molecular Mass, Moles, and Chemical Nomenclature

Molecular Mass and Percentage Composition

To calculate the molecular mass and determine the molecular weight of an item, we focus on the mass number (protons + neutrons). If the element is a molecule or compound, we add the atomic masses of the elements that compose it. Composition is calculated to find the percentage of the total mass that each element represents; this consists of dividing the molecular mass of an element by the compound's total mass and multiplying by 100 to find the percentage.

The Mole Concept and Avogadro's Number

Regarding quantitative substances, we use the mole. Because atoms and molecules are very small, we use this specific magnitude of substance (n). One mole of any determined substance is equivalent to 6.022 x 10²³ particles. It is important to keep in mind that although all moles contain the same number of particles, they do not have the same mass; for example, a mole of chlorine atoms weighs differently than a mole of silver atoms. We use a specific formula to convert between mass and moles.

6.022 x 10²³

Chemical Formulation and Nomenclature

A chemical formula is a symbolic representation of a molecule or a chemical structural unit. Nomenclature refers to the set of rules through which we name chemical compounds.

Valence and Oxidation Numbers

The concept of valence and the oxidation number refer to the capacity of an atom to join others and form a compound. In covalent compounds, this is equal to the number of bonds formed.

Binary Oxygen Compounds and Oxides

Binary oxygen compounds (oxides) are formed when oxygen combines with almost all chemical elements. In these oxides, oxygen acts with an oxidation number of -2.

• Writing Formulas: The first element is always followed by oxygen.
• Exchanging Valences: Elements exchange their respective valences to create the formulas.

Naming Systems

1. Systematic Nomenclature: This is the most direct method; it uses prefixes for naming based on the formula.
2. Stock Nomenclature: This method is used when we must deduce the valence of the acting elements. It does not always indicate the final result, but rather the initial oxidation state using Roman numerals without prefixes.