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Physical Properties of and Changes in Matter

Physical Properties of and Changes in Matter

The teacher understands physical properties of and changes in matter.

This competency looks at basic concepts in chemistry. Matter is a general term that refers to anything that has mass and volume—in other words, physical objects. For a general introduction to matter, visit the section on Matter in Bulk at the Wired Chemist.

Subtopics:

Physical Properties of Substances

The beginning teacher describes the physical properties of substances (e.g. density, boiling point, solubility, thermal and electrical conductivity).

Key Concepts:

  • Matter is anything that occupies space and possesses mass. Matter consists of atoms and other particles that have mass.
  • The density of matter of an object is its mass per unit volume. Density of gases and liquids vary with temperature.
  • The boiling point of an element or substance is the temperature at which the vapor pressure of the liquid equals the external pressure surrounding the liquid.
  • Solubility is the property of a solute (solid, liquid, or gas) to dissolve in a solvent (solid, liquid, or gas) to form a homogeneous solution (e.g., mixture) or solid.
  • Thermal conductivity is a measure of the ability of a material or object to conduct heat.
  • Electrical conductivity is a measure of the ability of a material or object to conduct electricity.

Resources:

Density. Density is explained both physically and mathematically with several examples in the Virtual Chembook from Elmhurst College.

Properties of Matter. The ChemEd site at Purdue University features a number of descriptive pages on properties of matter including the article entitled “Melting point, Freezing Point, Boiling Point,” which compares these three related properties.

Solubility. The ChemEd site at Purdue University discusses solubility and provides several examples of the equations for solubility and lists of soluble and insoluble salts.

Solubility in Liquid Solvents. Learn about solubility of salts and gas solutes in liquid solvents with this video from the Khan Academy.

Electrical and Thermal Conductivity.  Electrical and thermal conductivity (with examples for a variety of materials) are described on the NDT Resource Center site.

Solids, Liquids and Gases (States of Matter)

The beginning teacher describes the physical properties and molecular structure of solids, liquids, and gases.

Key Concepts:

  • The three classical states of matter that predominate on the surface of Earth are solids, liquids, and gases. However, most of the matter in the observable universe is in another state called plasma. The three classical states and plasma can change from one form to another with changes in temperature and pressure.
  • Solids are a state of matter consisting of tightly packed and strongly bound atoms or molecules. Solids are the densest state of matter and their atoms or molecules are arranged in either a regular geometric lattice or in an irregular (amorphous) arrangement that provides structural rigidity and resistance to change in shape or volume.
  • Liquids are a state of matter consisting of atoms and molecules bound together but unlike solids are able to change their shape to fit their containers. Liquids are nearly as dense as solids but are able to flow. Some liquids can be compressed while others are resistant to compression. Liquids exhibit surface tension that causes them to take spherical shapes to minimize surface area.
  • Gases are a state of matter consisting of atoms or molecules that move freely about in the absence of an applied electrical field. Gases are far less dense than liquids and are able to be compresses. Gases take the shape and volume of a container holding them. The movement of gas atoms or molecules exerts pressure during collisions that causes gas to expand infinitely when not held in a container or by a gravitational field. Temperature changes causes gas atoms and molecules to move slower (cold) or faster (hot). Changes in the movement of gas atoms and molecules, due to temperature changes, is an important factor in the movement of air in Earth’s atmosphere.
  • Plasma is a very low density state of matter similar to gas in which a portion of the atoms or molecules are ionized. Ionization (the presence of free electrons and positively charged atoms) can occur due to heating or to the application of an electrical field. Electrons, in excited states, release bits of light when they recombine with ions. This is the principle behind the light from auroras, fluorescent lights, and gas lasers. Because plasma is electrically charged (ionized) it responds strongly to magnetic fields. Lightning is a common example of a plasma.

Resources:

States of Matter. A simplified explanation, with illustrations, of the states of matter and their relationships to each other is given in the CHEM4KIDS site.

States of Matter. The three classical states of matter are explained with animations and a comparison table on the Purdue University chemistry site:

States of Matter Transitions. The two-way relationships between the four states of matter are illustrated in a basic flow chart.

Relationship between Molecular Structure and Physical Properties

The beginning teacher describes the relationship between the molecular structure of materials (e.g., metals, crystals, polymers) and their physical properties.

Key Concepts:

• Crystals are solid materials that have their atoms arranged in an orderly repeating pattern in all three spatial dimensions. Polycrystalline materials are solids composed of many microscopic crystals arranged in all directions. Most metals are polycrystalline. Amorphous materials are solids, such as glass, that contain no discernable crystalline structure.

• Metals are substances (element or compound) that conduct electricity and heat, and often also have luster and higher densities than non-metals. Atoms within a metal readily lose electrons from their outer shell, which accounts for the abilitiy of metals to conduct electricity, and also explains their tendency to form positive ions (cations). The majority of elements on the periodic table are metals.

• Polymers are large molecules composed of repeating structural units connected by covalent chemical bonds. The term “polymer” sometimes is used to refer to plastics, but it actually encompasses a large class of naturally occurring and synthetic materials with a wide range of properties.

Resources:

Introduction to Polymers. A lighthearted look at polymers for chemistry novices, created by the Department of Polymer Science, The University of Southern Mississippi.

Metals. Use this tutorial called Metal Basics from CHEM4KIDS to review the characteristics of metals. Clink on Alkali Metals to learn more.

Crystals. Visit What Is a Crystal from the University of California-Berkeley, for an introduction to the structure and chemistry of crystals and metals.

Click here for an illustration that shows the structural difference of crystals, metals (polycrystalline), and amorphous solids.

Physical Properties of Elements and Placements in the Periodic Table

The beginning teacher relates the physical properties of an element to its placement in the periodic table.

Key Concepts:

  • The periodic table is a graphic organizer for the elements and their properties. The different rows in the table are called periods. Elements are arranged in increasing order according to their atomic numbers (number of protons in the nucleus). The table enables users to identify the relative properties of the elements from their placement in the table.
  • Elements are arranged in the periodic table so that the atomic weights of elements increase from left to right within each row.

Resources:

Periodic Table Tutorial. Learn the basics about the periodic table in this interactive tutorial by the Annenberg Foundation.

Elements and the Periodic Table. The interactive Periodic Table Elements created by the Los Alamos National Laboratory provides introductory material, chemical properties, historical information, elements lists, and more.

The Ptable is an interactive periodic table that displays different properties of the elements, such as melting point, abundance, etc.

Physical and Chemical Changes in Matter

The beginning teacher distinguishes between physical and chemical changes in matter.

Key Concepts

  • Physical changes involve energy and states of matter, the substance itself is not changed. For example, cutting a piece of wood in half (a process that requires energy) yields two pieces of wood. Only the size of the pieces is different, not their composition. Melting an ice cube is another example of a physical change. In this case, water changes from a solid to a liquid state as a result of the addition of heat energy.
  • Chemical changes happen on a molecular level and alter the composition of the substance itself. Burning the wood from the previous example releases carbon dioxide and water, and leaves carbon-containing compounds behind that are different than the original wood. Upon completion of the chemical change, the wood no longer exists. In chemical changes, precipitates (formation of a solid in a solution) may be formed. Other kinds of chemical changes may show a change in color, such as when iron reacts with oxygen and acquires a reddish hue (rust).

Resources

Chemical and Physical Changes. The General Chemistry Online site briefly describes the difference between physical and chemical changes and lists several examples of each.

Applications to Processes and Situations in Life and Earth/Space Science

The beginning teacher applies knowledge of physical properties and of changes in matter to processes and situations that occur in life and earth/space science.

Key Concepts:

  • Life processes are the result of chemical changes. Food (energy) is taken in and various chemicals, such as water and oxygen, are processed and recombined in chemical reactions that produce living tissue and motion. Metabolism (Greek for change) is the chemical reactions that happen in the cells of living things that sustain life.
  • Physical changes in the solid and liquid parts of planet Earth, are common (e.g., physical weathering, erosion, and deposition). Changes of state of water, driven by temperature, are physical changes. Water freezes into snow and ice, then melts into liquid water, and then evaporates into water vapor. While the appearance of water changes, it is still water.
  • Chemical changes occur in Earth materials when rocks are dissolved (chemical weathering) such as when limestone is dissolved by carbonic acid to form caves or by acid rain. Other examples include the formation of metamorphic rock and reactions in the atmosphere, such as ozone formation and degradation.

Resources:

Physical and Chemical Changes. The General Chemistry Online site briefly describes the difference between physical and chemical changes and lists several examples of each.

Water Cycle Physical Changes. The physical changes that occur in water as a part of the water cycle can be observed in these animations from NASA.

Weathering and Erosion. The difference between weathering (physical and chemical) and erosion, as they relate to physical and chemical changes in earth materials, is described in this United States Geological Survey page.

Changes in Living Systems. How the chemical reactions (metabolism) in the body’s cells sustain life is described in an article from the KidsHealth site.



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