CH.3+ States and Properties of Matter and Energy

Basic Chemistry: Chapter 3 - Matter and Energy

Pure Substances: Elements and Compounds

  • A pure substance is defined as:

    • A type of matter with a fixed or definite composition.

    • An element, which consists of only one type of atom.

    • A compound, made up of two or more elements that are chemically combined in the same ratio.

Elements

  • Elements are:

    • Pure substances that contain only one type of material.

    • Examples of elements include:

    • Copper (Cu)

    • Lead (Pb)

    • Aluminum (Al)

    • Note: An aluminum can may consist of many atoms of aluminum.

Compounds

  • A compound is defined as:

    • Consisting of two or more elements combined in a definite ratio.

  • Examples of compounds include:

    • Water (H₂O): consists of two atoms of hydrogen (visualized as white) for every one atom of oxygen (visualized as red).

    • Hydrogen peroxide (H₂O₂): consists of two atoms of hydrogen (white) and two atoms of oxygen (red).

Classification of Matter

  • Matter can be classified into:

    • Elements

    • Pure Substances (including both elements and compounds)

    • Mixtures:

    • Homogeneous

    • Heterogeneous

  • Examples:

    • Copper atoms, Water molecules, Brass (a mixture of copper and zinc atoms).

Mixtures

  • A mixture is characterized by:

    • Consisting of two or more substances that are mixed together but not chemically combined.

    • The substances present can be in different proportions and can be separated by physical methods.

  • Example: Mixture of spaghetti and water can be separated using a strainer (a physical method of separation).

Homogeneous Mixtures

  • A homogeneous mixture is defined as:

    • Having a uniform composition throughout the sample.

    • The distinct parts of the mixture are not visible.

  • Example: Brass, which is a homogeneous mixture of copper and zinc atoms.

Heterogeneous Mixtures

  • A heterogeneous mixture is characterized by:

    • A composition that varies from one part of the mixture to another.

    • The distinct parts of the mixture are visible.

  • Example: A mixture of water and copper forms a heterogeneous mixture.

Sample Problem: Classifying Mixtures

  • Task: Classify each of the following as a pure substance (either element or compound) or a mixture (homogeneous or heterogeneous):

    • a. Copper in wire

    • b. Chocolate-chip ice cream

    • c. Nitrox (a mixture of oxygen and nitrogen for scuba tanks)

    • d. Cookie with raisins

Solution to Sample Problem

  • a. Copper in wire:

    • Classification: Pure Substance (Element)

  • b. Chocolate-chip ice cream:

    • Classification: Mixture (Heterogeneous)

    • Reason: Mixture consists of two or more substances together, non-uniform distribution.

  • c. Nitrox:

    • Classification: Mixture (Homogeneous)

    • Reason: Uniform composition of nitrogen and oxygen.

  • d. Cookie with raisins:

    • Classification: Mixture (Heterogeneous)

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