Unit III: Properties of Matter

 

Introduction

It is difficult to conceptualize something as small as an atom, and, yet atoms are more pervasive than any thing we know. All matter is made up of atoms. In fact, all matter is made up of just 109 distinct atoms! In studying the properties of matter we will explore the atomic nature of matter in its four states—solids, liquids, gasses, and plasmas. This unit is divided into three sections: atomic nature of matter, solids, liquids, and gasses and plasmas. Studying this will take approximately two and a half weeks. Intended Learning Outcomes
 
General Instructional Objectives (and corresponding Specific Learning Outcomes) Unit Content
Knows terms

Understands the meaning of terms

atom, Avogadro’s number, molecule, density, elasticity, buoyant force, plasma, surface tension, capillarity, compound, mixture, antimatter 
Understands scientific concepts atomic structure, Brownian motion, states of matter, the periodic table, atomic bonding, scaling, crystal structure, Archimedes' Principle, Pascal's Principle, Boyle's Law, Bernoulli's Principle, Hooke’s Law, principle of flotation 
Knows all laboratory procedures

Prepares a plan for an experiment

Participates in classroom activities

Respects the scientific process

Displays a scientific attitude

Demonstrates skills in laboratory work

All content

 

Instructional Foci

Experiments: Archimedes’ principle, Hooke’s Law; demonstrations: Bernoulli’s principle, crystal structure using blocks, principle of flotation, surface tension, capillarity, compound, mixture; class makes their own "periodic table" from different shapes of pasta, class discussion, homework (including measuring the weight of their car), quizzes, readings, questions for thought from the Flying Circus of Physics Teaching Strategies The first section of this unit, the atomic nature of matter, should begin with a discussion of atoms. The size, number, and agelessness of atoms are particularly important concepts to get across to the students. In addition, the teacher should discuss how atoms jiggle perpetually (Brownian motion). Atoms combine to form molecules. When studying molecules it may be helpful to use models of molecules (water—H2O, methane—CH4, ozone—O3) made of styrofoam balls or purchased from science demonstration supply catalogs. With models students quickly realize that atoms are joined in well defined ways to form molecules. Also, using models is a good way to introduce molecular and atomic masses. Then more complex models can be used to illustrate the difference between elements, compounds, and mixtures. Physical examples of elements, compounds and mixtures should be demonstrated also. Gold, water, and salt with sand are good examples of each, respectively. A brief discussion of the structure of the atom should follow this demonstration. Once students have a basic understanding of the atomic structure, and before you introduce them to the periodic table, an in class project of forming their own organizational system on a chart should be done. For example, students could be asked to organize different shapes of pasta into a pattern to fit a chart. This causes students to make a conscious commitment to an organizational scheme. Hopefully they are then more likely to revise their scheme to the scheme of the periodic table. Otherwise, without introducing organizational schemes, they often lose the meaning of the ordered nature of the periodic table. Following the discussion of the periodic table should be a brief discussion of the different states of matter and antimatter.

The next section explores the solid state of matter. This discussion should begin with crystal structure, which is what many solids are made of. Blocks can be purchased which illustrate each of the crystal structures, but too much emphasis should not be placed on this. Styrofoam balls arranged to represent, for example, a crystal of sodium chloride (NaCl) can just as easily be used. Then a discussion of density as related to crystal structure (spacing of the atoms) and mass would be appropriate. Changes in the arrangement and bonding of atoms in a material resulting from a deforming force are know as elasticity. When studying elasticity, Hooke’s law should be demonstrated using springs with varying weights (illustrating that the amount of stretch is proportional to the force applied or weight). This discussion will naturally lead to the discussion of tension and compression. Tension and compression rules can be illustrated using arches and domes in architecture. This is why the Astrodome in Houston does not need any columns to support it. Other examples are the Capitol, Eskimo igloos, Roman aqueducts, and the Jefferson Monument. Finally, there should be a brief discussion of scaling.

The liquid state of matter will be explored in this section. We will begin with a discussion about pressure in a liquid. An illustrative example is swimming under water—as you increase in depth you feel an increase in pressure against your eardrum. In addition, when you try to pick someone or something up under water it seems lighter than when you try to lift it out of the water or above the surface. This is due to buoyant force, which depends on the volume of the displaced object, not the weight of the displaced object. A demonstration for this and Archimedes’ Principle follows: using a beaker full of water immediately next to an empty one being held up by a scale, lower a weight, being held up by a scale, into the beaker of water and watch as the scale attached to the weight decreases as the water pours into the empty beaker, and its weight increases. Notice the initial weight of the scale is equal to the weight of the immersed weight plus the weight of displaced water (Archimedes’ Principle). Then demonstrate and discuss the density effects on submerged objects if the object is (1) denser than the fluid (a penny in water), (2) less dense than the fluid (a piece of styrofoam in water), (3) equal density to the fluid (a fish). This will naturally lead to a discussion about flotation. Talk about canoes or ships that, when weighing more float lower (displace more) in the water than when empty or weighing less (displace less)—a floating object displaces a weight of fluid equal to its own weight. Then discuss Pascal’s Principle, an example of which is an automobile lift. Surface tension and capillarity will be the next topics of study. An excellent example relevant to students’ lives is that of soap weakening the cohesive forces between water molecules, hence reducing surface tension. To illustrate this interaction, mix oil and water in a jar then calculate the time it takes for them to separate. Now add soap to the mixture and re-mix it, calculating the time it takes to separate the oil from the water. It should take much longer with the soap in the mixture since soap breaks the surface tension around each oil (dirt) particle. This is what allows the water to surround the dirt particle and carry it away with rinsing. To illustrate capillarity pass around different diameter test tubes filled with water and not the capillary action in each. Also, dip the tip of a paper towel in water and notice how the water seeps up higher than the water level due to capillary action.

In the final section of this unit we will explore gases and plasmas. The atmosphere is a relevant illustration of gases doing their thing. The teacher should also discuss atmospheric pressure, barometers and Boyle’s Law. An excellent homework exercise for understanding the concept of pressure is to have the students measure the force or weight of their car using the area of and pressure in their tires. Give students a large pieces of graph paper in square centimeters. They should trace the area of a tire, assuming the other four tires have the same area, and determine the pressure in the tire (by using a pressure gauge or by assuming the pressure in the tire is as it should be according to the pressure requirement of the tire). They should then convert the area traced on the graph paper from square centimeter to square inches. This number of square inches multiplied by the pressure of the tire in pounds per square inch will give them the force or weight of their car! Then discuss the buoyancy of air, which is just like the buoyancy of water, but in air. Following that should be a discussion of Bernoulli’s Principle. Only after the students have some grasp of the this principle should a demonstration of it in action be given. The demonstration could use a ball tied to a string that is then held under a steam of running faucet water. Then pull the string away from the steam and notice the ball stays in the running water. This is, of course, due to the decrease in pressure from the increase in speed of the water causing the ball to seek the area of lesser pressure or be pushed from the higher pressure surrounding air into the lower pressure stream of water. Airplanes, tornadoes (and torn off roofs), and spin on a tennis ball are also relevant applications of Bernoulli’s Principle. This section will be concluded with the discussion of plasma as the fourth state of matter. A discussion of fluorescent lamps, which use a plasma consisting of low-pressure mercury vapor, would be appropriate.
 

Special Notes
 
  1. All labs should be preceded by an in class demonstration by the teacher of the proper procedures. After viewing the demonstration, students’ homework should be to prepare a plan for the experiment. Due to the time constraints of high school classes it is imperative that students have thought through the experiment before class. You, the teacher, need to know that they are aware of proper equipment set-up and safety precautions as well as appropriate hypothesis development, variable controls, and observation and measurement procedures.
  1. Labs can be found in Laboratory Manual in Conceptual Physics by Bill Tillery.
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