Foundations of Chemical Principles

Properties of Matter

Properties of matter help us describe and identify substances.

General Properties

These are properties common to all matter, such as mass and volume. They do not help distinguish one substance from another.

Characteristic or Intensive Properties

These properties are unique to a specific substance and do not depend on the amount of matter present. They are useful for identifying a substance. Examples include density and melting point.

Extensive Properties

These properties depend on the amount of matter present. Examples include mass and volume.

Fundamental Chemical Concepts

Relative Atomic Mass

The relative atomic mass of a chemical element is the ratio of the average mass of atoms of an element to one twelfth of the mass of an atom of carbon-12. It is a dimensionless number.

Atomic Mass Unit (amu)

The atomic mass unit (amu) is defined as one twelfth of the mass of an atom of the carbon-12 isotope. It is approximately equal to 1.66 x 10^-27 kg.

The Mole

The mole is the amount of substance that contains as many elementary entities (atoms, molecules, ions, etc.) as there are atoms in 0.012 kilograms of carbon-12.

Molar Mass

The molar mass of a substance is the mass of one mole of that substance. For atoms, the molar mass in grams per mole (g/mol) is numerically equal to its relative atomic mass.

For a compound, the molar mass in grams per mole (g/mol) is numerically equal to its relative molecular mass.

Avogadro's Number (N_A)

One mole of any substance contains Avogadro's number of elementary entities. Avogadro's number is approximately 6.022 x 10²³.

Chemical Formulas

Empirical Formula

The empirical formula indicates the elements present in a compound and the simplest whole-number ratio of their atoms.

Molecular Formula

The molecular formula indicates the elements present in a compound and the exact number of atoms of each element in a molecule of the compound.

Dalton's Atomic Theory and Chemical Laws

Dalton's atomic theory provides explanations for fundamental laws of chemical combination.

Law of Conservation of Mass

In a chemical reaction, atoms are neither created nor destroyed. They are only rearranged to form new substances. Therefore, the total mass of the reactants equals the total mass of the products.

Law of Definite Proportions

A chemical compound always contains the same elements in the exact same proportion by mass, regardless of the source or size of the sample. For example, hydrochloric acid (HCl) always consists of hydrogen and chlorine in a fixed mass ratio.

Law of Multiple Proportions

If two elements can combine to form more than one compound, then the masses of one element that combine with a fixed mass of the other element are in ratios of small whole numbers. For instance, oxygen and sulfur can form different compounds (like SO₂ and SO₃). The masses of oxygen that combine with a fixed mass of sulfur in these compounds are in a simple whole-number ratio.

Volumetric Laws of Gases

Gay-Lussac's Law of Combining Volumes

When gases react at constant temperature and pressure, the volumes of the reactants and products that are gases bear a simple whole-number ratio to one another.

Examples:

• 1 volume Hydrogen + 1 volume Chlorine → 2 volumes Hydrogen Chloride
• 2 volumes Hydrogen + 1 volume Oxygen → 2 volumes Water Vapor
• 3 volumes Hydrogen + 1 volume Nitrogen → 2 volumes Ammonia