The Greeks were the first in recorded history to ponder extensively about the nature of matter. Their speculations on this issue were left mainly to philosophers who drew their conclusions from observation and reasoning. One of the earliest of these thinkers was Thales who, having observed that water turned to air and steam when heated and solid when frozen, reasoned that all matter was derived from water. Heraclitus, however, believed that the ever-changing nature of fire was compatible with that of matter and thus reasoned that fire was the origin of all matter. Parmednides provided a counter argument; he believed that change was inconceivable since change requires the creation of something new from nothing. This Parmednides argued is impossible, instead he believed that the universe is unchangeable and that change is only an illusion.
It was the atomists (i.e. Democritus and Leucippus) who provided the most accurate and concise depiction of matter at that time. According to the atomist, the basic component of matter (atom) was tiny particles that were qualitatively similar. Some atoms had hooks or eyes, and others had grooves, humps, or depressions that allowed them to unite in various ways and numbers. Until Dalton, this was the most accurate interpretation of matter in that atoms were described as the most basic form of all substances. The atomists’ theory was an early version of the current atomic theory.
This section of the unit will focus on how philosophers of antiquity defined matter and the bases for such definition. It will involve reading from ancient Greek literature, class discussion of ideas from these readings, development of a class definition of matter based on deductive reasoning, and journal writing. The guiding question for this section is, “what is matter?”.
This section of the unit will partially fulfill Content Standards on scientific inquiry of New Haven Public Schools’ Academic Performance Standard by:
Encouraging student to communicate and defend an argument
Helping students recognize that the results of scientific inquiry emerge from different types of investigations and public communication among scientist
The time limit for this section is 5-7 45 minutes class periods. It will be primarily taught using a modified Socratic Seminar format designed for 30-45 minutes class period. In additions students will keep a journal of the daily discussions which will be later used to develop a class definition of matter.
The Socratic Seminar is a discussion and debate forum originally used by Socrates about 2400 years ago. Through the seminar, students and teacher, functioning at an equal level, pulling from the experiences, ideas, and opinions of each other. Rather than becoming passive learners, students are actively engaged in conversations with their teachers and fellow “classmates”. Essential to the success of a Socratic Seminar is the establishment of an environment that is non-threatening and which encourage students to freely express their opinions. The teacher must not dominate the discussion or establish an environment where he/she is seen as an authority on a specific issue.
In the classroom, Socratic Seminars is set up with two groups of students. Each group comprises roughly a half of the class. Students of Group 1 will become actively engaged in the discussion while Group 2 will act mainly as observers and will be responsible for recording the discussion. Chairs are arranged to form an inner (active participants) and outer (observers) circle. The teacher should participate mainly as an observer or a passive participant. The Socratic Seminar consists of four important components:
a piece of text which introduces a specific idea
questions presented by the students that relate to the text
a seminar leader who functions more as a coach
Students will be given a piece of text1 a day prior to the seminar and will be required to write a journal response to this reading as homework. This will encourage students to begin thinking about the idea presented. The texts to be used are as follows.
Questions will be generated as the discussion proceeds. The teacher must assign one or two students to lead the discussion. Prior to the journal writing homework, the leader(s) may cue students in on possible direction for the discussion and ask students to address the reading from a given prospective. The leader must have a series of questions, viewpoints, concerns, etc. regarding the reading that will be used to keep the dialogue flowing. Each seminar will begin with the inner circle reading their journal entry. Students may pose questions or make comments to any individual regarding a specific idea presented in the journal. A dialogue will often following smoothly. Before the close of the seminar the inner circle must debate in favor of or against the concepts, ideas, or theories presented in the text.
The leader must not be the center of attention but must instead serve to keep the momentum of the discussion moving. He/she must remember that they are more of a participant than a leader and must allow all participants equal opportunity to express their ideas.
Students in the outer and inner circle will rotate with each seminar. It is important that the participants, both inner and outer circle carefully study and think about the text. Journal writing is designed specifically to encourage student to take this task seriously. The teacher must reinforce the importance of a carefully thought out and well written journal response. The teacher may choose to collect and grade the journals.
The role of the inner circle participant has been clearly outlined. Outer participants will be responsible for recording the important points from the discussion and than summarizing them after the seminar discussion. Outer circle participants may be assigned to look from arguments that either support or oppose the text. Ideally these students can display charts that outline the pros and cons of each seminar.
The Laws that cleared the Way
The ancient philosophers laid the foundation for a new way of looking at nature. Much of the ideas about matter provided by the Greeks were based on logic and reasoning rather than experimentation and observation. Consequently, little proof was provided to support the ancient claims. To answer the question “what is matter?” the latter two could not be ignored.
Two major discoveries on the principle of chemical behavior path the way to providing a working answer. First was the discovery of the law of conservation of matter by Antoine Lavoisier. In his experiment, Lavoisier measured the masses of substances before and after chemical reactions and found that the masses always remained constant. From this he concluded that matter couldn’t be created or destroyed, but instead is conserved. The second discovery was the law of constant composition by Joseph Proust who observed that a given compound always maintained the same elements in the same proportion of mass regardless of quantity of the compound. This section will explore these two laws and afford student an opportunity to improve on the definition of matter.
This section of the unit will partially fulfill Content Standards on scientific inquiry of New Haven Public Schools Academic Performance Standard by:
1. Designing and conducting scientific investigations, while taking into account the proper safety precautions
2. Using mathematics in scientific inquiries
The time limit for this section is 5-7 45 minutes class periods. It centers on two laboratory exercises and class discussion.
Discussion and Laboratory Exercise – Matter is Conserved
Students will have a greater appreciation for the law of conservation of matter if they can deduce this law for themselves. A day prior to the lab investigation the class will engage in a discussion on an experiment performed by Lavoisier and the previously documented observations by others that compelled him to carryout his experiment. The discussion will center on the two experiments described below. A Socratic seminar will be ideal here:
Experiment 1 (alchemist) - when water is boiled for sometime in a glass or ceramic container solid residue tends to collect in the container at the end. The alchemist interpreted this as the transformation of water into earth under the influence of fire.
Student will be asked to argue for or against the credibility of the alchemist experiment and the validity of their conclusion. They will then consider methods of improving the experiment by using controls. Once a suitable experimental plan is outlined students will be presented with a description of Lavoisier’s experiment for comparison to the alchemist’s.
Experiment 2 (Lavoisier) – Lavoisier boiled a weighed quantity of water in a weighed pelican (a closed vessel having a long neck bent back upon itself, picture) for 100 days. At the end of the boiling the total weight of the pelican and its content had not changed. This clearly showed that the fire had not contributed any new mass to the system. Lavoisier, however, observed that the mass of the pelican had decreased, but the mass of the content (water and residue) had increased by an amount equivalent to what was loss from the pelican. He concluded that the solid material must have come from the glass.
Student must then write in their journals their interpretation of how Lavoisier’s finding affects the alchemist’s conclusion and how it affects the class’ definition of matter.
The laboratory exercise will involve a study of mass changes in the two chemical reactions shown below. (For a complete lab handout and description of procedures please reference Wagner et al; page 47). Through this lab student will observe Lavoisier’s law of conservation of matter:
Na2CO3(aq) + CaCl2(aq) ( 2NaCl(aq) +CaCO3(s)
CaCO3(s) + H2SO4(aq) ( CaSO4(s) + H2O + CO2(g)
The idea is that the mass of components of Reaction 1 will remain constant throughout the reaction, while that of Equation 2 will decrease. The decrease is expected because the gaseous substance (CO2) produced will leave the reaction system. Student will be expected to analyze and make assumption as to why that difference in mass occurred in Reaction 2 but not in Reaction 1. They will also be expected to draw conclusions in reference to Lavoisier’s experiment. The exercise will close with the class collectively developing of a law (law of conservation of matter) that is supported by the experiments.
Discussion and Laboratory Exercise – Matter Maintains a Definite Composition
Students will explore the law of constant composition by observing the changes in mass of melons following overnight dehydration. The objective is to obtain a clear and accurate understanding of the concepts of the lawpercent composition for the components of a given substance remain constant regardless of the amount of substance present.
Prior to the laboratory exercise students must understand how to calculate percentage compositionthe teacher may chose to provide students will homework practice problems on percentage composition.
The exercise will involve weighing out various quantities of sodium carbonate hydrate (Na2CO3(10H2O) and determining the percent composition of water in the hydrate. Students will observe that regardless of the amount of sample analyzed, the percent composition remains relatively constant. (The complete lab handout with procedures can be found on page 21 of Heisig’s Experiment in Chemistry for Engineering Students).
Dehydration is carried out in a clean dry crucible and takes about 30 minutes. Quantities should range from 1-5 grams and should be placed in the crucible. Students than weigh the crucible, hydrate, and cover together. The crucible is heated on a triangle with a small flame until the residue becomes powdery. This will take about thirty minutes or until total mass remains constant. While students wait for dehydration to complete they will respond in their journals to the following question: How will the amount of hydrate used affect the percent composition?
The exercise is followed by a class discussion lead by the teacher. The purpose of this discussion is to clearly establish the law of conservation of matter by drawing on the conclusion generated from the laboratory exercise.
The Origins of Dalton’s Atomic Theory
An answer to the matter question finally began to take shape with the work of John Dalton. By observing previous experiments and through his research, Dalton concluded that the properties of matter could be explained in terms of an atom. Dalton’s atomic theory of matter was based on the following postulates:
1. Each element is composed of extremely small particles called atoms.
2. All atoms of a given element are uniquely identical.
3. Atoms cannot be created of destroyed.
4. A given compound always has the same relative number and kinds of atoms.
Dalton’s theories were developed from a number of observations that either contradicted of shed light on previous work. In ‘Theory of the Absorption of Gases by Water’ Dalton considered that different types of substances (atoms and molecules) were physically unique in terms of quantity and mass. He wrote
“The greatest difficulty attending the mechanical hypothesis arises from different gases observing different laws. Why does water not admit its bulk of every gas alike? …I am nearly persuaded that the circumstance depends upon the weight and number of ultimate particles of several gases: those particles that are lightest and single being least absorbable and the other more as they increase in weight and complexity.”
Dalton is hypothesizing that physical properties (i.e. density, texture, etc) of matter may depend on properties (mass and quantity) of some basic component (atom).
This part of the unit will explore Dalton’s Atomic Theory through the study of various works by Dalton and others who contributed to this theory.
This section of the unit will partially fulfill Content Standards on scientific inquiry of New Haven Public Schools Academic Performance Standard by:
1. Designing and conducting scientific investigations.
2. Incorporating technologies.
3. Communicating and defending a scientific argument.
4. Using mathematics to analyze and solve problems.
5. Recognizing that results of scientific inquiry emerge from different types of investigations and public communication among scientists.
Working in groups of three, student will make use of Internet and library resources to research Dalton’s atomic theory. In this assignment students will be required to research and discuss the experiments and observations made by Dalton’s and others of his time which ultimately lead to the development of the atomic theory. Accompanied by a 3-5-page paper, each group will present their research to the class. A question answer section will follow each presentation. This part of the unit will conclude with students designing and constructing a model impression of an atom that must be supported with cited experimental evidence.
Students will be given 3 days of class time to research and organize their report. It is essential that each group have access to the Internet and that the prescribed time is set aside for groups to perform their research. The teacher must set daily objective that will keep students on task.