Notes on 1.3 The Classification of Matter: States, Composition, and Changes
States of Matter
There are three states of matter: gaseous, liquid, and solid.
A gas is made up of particles that are widely separated and will expand to fill any container; it has no definite shape or volume.
A liquid has a definite volume but no definite shape; it takes on the shape of its container and its particles are closer together than in a gas.
A solid consists of particles that are close together, often with a regular and predictable (crystalline) pattern; a solid has fixed volume and fixed shape. The particles in a solid are more organized than in a liquid or gas.
Attractive forces between particles are very pronounced in solids and much less so in gases.
Learning Goal 5
Describe the properties of the solid, liquid, and gaseous states.
Learning Goal 6
Classify matter according to its composition.
Composition of Matter
Matter can be classified by its state (solid, liquid, gas) and by its composition.
All matter is either a pure substance or a mixture.
A pure substance has only one component. Example: water, which is made up of two hydrogen atoms and one oxygen atom—i.e., molecules.
Pure Substance
A pure substance has only one component.
All pure substances are either elements or compounds.
An element is a pure substance that generally cannot be changed into a simpler form of matter.
Examples: Hydrogen, Oxygen.
A compound is a substance resulting from the combination of two or more elements in a definite, reproducible way.
Example: water, , formed from Hydrogen and Oxygen.
Mixture
A mixture is a combination of two or more pure substances in which each substance retains its own identity.
Ethanol and water can form a mixture; they coexist as pure substances and do not undergo a chemical reaction.
A mixture has variable composition; there are infinite possible combinations of the components.
A mixture may be homogeneous or heterogeneous.
Homogeneous Mixture
Has uniform composition; particles are well mixed or thoroughly intermingled.
A homogeneous mixture is described as a solution.
Examples:
Ethanol in water (a solution).
Air (a gaseous solution).
Heterogeneous Mixture
Has a nonuniform composition.
Examples:
Salt and pepper.
Concrete (nonuniform mixture of stone, sand, cement).
Figure references and broader context
More than 100 elements have been characterized; a complete listing is in Chapter 2.
A detailed discussion of solutions (homogeneous mixtures) and their properties is presented in Chapter 6.
Figure 1.4 illustrates matter by composition (pure substances vs mixtures).
Figure 1.5 illustrates classes:
(a) pure substance (water) with a single component,
(b) homogeneous mixture (blue dye in water) with uniform distribution,
(c) heterogeneous mixture (mineral orbicular jasper) with nonuniform distribution.
Example 1.2: Classifying Matter by Composition
Seawater is a heterogeneous mixture.
In seawater, solid particles (sand, vegetation, perhaps a small fish) are not uniformly distributed, indicating a heterogeneous mixture.
Practice Problem 1.2
Classify each material as a pure substance, a homogeneous mixture, or a heterogeneous mixture:
a. ethanol
b. blood
c. an Alka-Seltzer tablet fizzing in water
d. oxygen being delivered from a hospital oxygen tank
Learning Goal 6 (reaffirmed)
Classify matter according to its composition.
For further practice: Questions 1.53 and 1.54.
Physical Properties and Physical Change
Water is notable because it can exist in all three states over a reasonable temperature range; this exemplifies physical changes.
A physical change is a change in appearance without changing the composition or identity of the substance.
Example: melting ice to form liquid water. The substance remains water (composition and identity unchanged).
The melting and freezing cycle can repeat, illustrating the retention of the identity of water molecules.
A physical property can be observed or measured
without changing composition or identity.
Examples of physical properties: melting point and boiling point of water (these are physical properties).
A practical application of separating materials based on physical properties is shown in Figure 1.7 (e.g., magnetic separation).
Separation by physical properties
Magnetic separation: magnetic iron can be separated from nonmagnetic substances.
Light is the energy needed to drive many reactions; chlorophyll absorbs light to convert light energy to chemical energy.
Chemical Properties and Chemical Change
In contrast to physical properties, chemical properties arise from a change in composition and can be observed only through chemical reactions.
In a chemical reaction, substances are converted to one or more different substances by rearranging, removing, replacing, or adding atoms.
Example: photosynthesis can be represented as:
Reactants:
The physical properties of the reactants and products differ (CO₂ and O₂ are gases at room temperature; H₂O is a liquid; sugar is a solid).
A chemical property of is its ability to form sugar under certain conditions.
The process of formation of sugar is a chemical change; the term chemical reaction is synonymous with chemical change.
Summary connections
States of matter (gas, liquid, solid) are fundamental to understanding material properties and behavior in different environments.
Composition (pure substances vs mixtures) clarifies how substances interact and whether they retain identity after mixing.
Distinguishing physical vs chemical properties/changes helps predict how substances will behave under physical manipulation (melting, boiling, separating) vs during chemical reactions (recombinations, new substances formed).
Real-world relevance includes weather processes (water cycle), material separation in recycling, and biological processes like photosynthesis.