Chemistry Principles: Matter, Mixtures, and Laws

Principles of Chemistry

Matter and Chemistry

Mass is the fundamental characteristic of matter.

Chemistry is for studying the nature of matter and changes that affect nature.

Physical changes do not alter the nature of substances; chemical changes do.

Pure Substance

A pure substance has a definite, constant composition, specific physical and chemical characteristics, and cannot be separated into other substances by physical methods.

Mixture

A mixture has variable composition and properties related to its components.

Mixtures can be homogeneous or heterogeneous.

Separation of Mixtures

The components of mixtures can be separated by physical methods that do not alter the nature of the substances. Examples include:

  • Filtration
  • Centrifugation
  • Crystallization
  • Distillation
  • Chromatography

Element

An element is a substance which, when combined with other elements, forms compounds and cannot be decomposed into simpler substances.

Compound

A compound is a substance formed by two or more elements, which can be decomposed into these elements.

Law of Conservation of Mass (Lavoisier)

In a chemical reaction, mass is conserved.

Law of Definite Proportions (Proust)

When two elements combine to form a compound, they always do so in the same mass ratio.

Law of Multiple Proportions (Dalton)

If an element reacts with another, forming different compounds, then the masses of the other element are in a simple numerical relationship.

Law of Combining Volumes (Gay-Lussac)

The volumes of gases in a chemical reaction are in a simple and whole-number relationship.

Dalton’s Atomic Theory

Matter is made of tiny atoms, indivisible and unchangeable.

The atoms of an element are all equal and are differentiated from other elements by mass and properties.

The atoms of compounds are formed by joining atoms of elements in a consistent and simple numerical relationship, and they are equal in mass and properties.

Avogadro’s Molecular Theory

The ultimate particles forming gases are not atoms but molecules, or clusters of atoms with a fixed composition.

In equal volumes, measured under the same conditions of pressure and temperature, all gases have the same number of molecules.

Elementary Particles: Current Concept

Particles that are not divisible into others: quarks and leptons.

Atoms: Current Concept

Grouping of protons and neutrons (forming a nucleus) and electrons moving around.

Groups of Atoms: Current Concept

Atoms are organized into discrete groups or molecules and large clusters or networks.

Element: Current Concept

A substance consists of a single type of atom.

Compound: Current Concept

A substance consists of more than one kind of atom.

Proximate Composition

The composition of a pure chemical substance is expressed as a percentage by mass of its components.

Empirical Formula

The empirical formula shows the proportion of the different elements.

Molecular Formula

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