📚 Study Guide: The Atom and Classification of Matter
I. Classification of Matter
Matter is anything that has mass and volume, and it can exist as a solid, liquid, or gas.
Matter is classified into two main categories: Mixtures and Pure Substances.
ClassificationDefinitionSubcategoriesMixtures
Combinations of matter that can be separated by physical means and do not have a definite
chemical composition. Composed of more than one type of molecule.
Heterogeneous Mixtures (Mechanical Mixtures) - Individual components are visible (e.g.,
chocolate chip cookie, tossed salad).
Homogeneous Mixtures (Solutions) - Individual components are NOT visible and have a
uniform composition (e.g., sugar water, air).
Pure Substances
Composed of only one type of molecule and have a definite chemical composition.
Elements - Cannot be broken down into simpler substances (e.g., Gold {Au}, Oxygen.
Compounds - Two or more different elements that have been chemically combined. Can be
broken down into simpler substances by chemical means (e.g., Water {H2O), Table Salt (NaCl)
II. Atomic Structure and History
A. Key Terminology
● Atoms: The building blocks of matter. They cannot be broken down into simpler substances.
● Elements: The names given to atoms with specific properties, defined by the number of protons in
the nucleus (e.g., Carbon is any atom with 6 protons).
● Molecules: Groups of atoms bonded together. These can be atoms of the same element (e.g.,
diatomic molecules like or different elements.
● Compounds: Chemical substances in which two or more DIFFERENT elements are bound together.
I. Classification of Matter
Matter is anything that has mass and volume, and it can exist as a solid, liquid, or gas.
Matter is classified into two main categories: Mixtures and Pure Substances.
ClassificationDefinitionSubcategoriesMixtures
Combinations of matter that can be separated by physical means and do not have a definite
chemical composition. Composed of more than one type of molecule.
Heterogeneous Mixtures (Mechanical Mixtures) - Individual components are visible (e.g.,
chocolate chip cookie, tossed salad).
Homogeneous Mixtures (Solutions) - Individual components are NOT visible and have a
uniform composition (e.g., sugar water, air).
Pure Substances
Composed of only one type of molecule and have a definite chemical composition.
Elements - Cannot be broken down into simpler substances (e.g., Gold {Au}, Oxygen.
Compounds - Two or more different elements that have been chemically combined. Can be
broken down into simpler substances by chemical means (e.g., Water {H2O), Table Salt (NaCl)
II. Atomic Structure and History
A. Key Terminology
● Atoms: The building blocks of matter. They cannot be broken down into simpler substances.
● Elements: The names given to atoms with specific properties, defined by the number of protons in
the nucleus (e.g., Carbon is any atom with 6 protons).
● Molecules: Groups of atoms bonded together. These can be atoms of the same element (e.g.,
diatomic molecules like or different elements.
● Compounds: Chemical substances in which two or more DIFFERENT elements are bound together.
