Particles

Particles

Particles

Level: 7th Grade
Time Frame: 1 Quarter
Description: Students will learn that all matter is composed of particles. Atoms combine to form molecules and compounds. Characteristics and movement of particles in solids, liquids, and gasses are compared. History and development of atomic structure theory is described and modeled.

Overview
Activity List
Learning Objectives
Standards
Resources

Unit Overview
The Champaign elementary curriculum includes a “matter” unit in 5^th grade in which students use a wide array of (initially) unidentified common substances to explore the following: basic characteristics of matter, solubility, state (solid and liquid), and observable signs of physical and chemical changes. The 6^th grade students have a text-based unit on matter and chemistry that builds and expands on that knowledge, with activities and information that are somewhat more sophisticated and structured than those in the 5^th grade unit. In 6^th grade, the students are introduced to elements and compounds, but not to atoms.

In this 7^th grade unit, the historical development of the “particle model” of the nature of matter is introduced, and this particle/atom model is used to redefine some basic chemistry concepts such as state of matter, the effects of heating/cooling, and the conservation of matter. The structure of the atom is introduced at the end of the unit.

Middle school teachers should be aware that there is disagreement as to the appropriateness of this topic at the middle school level. In the (earlier) Benchmarks for Science Literacy, the introduction of the particle nature of matter is supported and even emphasized at the middle school level. However, the introduction of the structure of the atom is discouraged. The (newer) National Science Education Standards discourage even the introduction of the “particle (atom) model” at the middle school level, with the rational that students don’t truly understand it, and so time is better spent on the observable (macroscopic) properties of, and changes in, matter.

The Illinois Learning Standards and Performance Descriptors appear to be modeled after the Benchmarks for Science Literacy, and this is one rationale for including this unit in the curriculum. The last, very short section on atomic structure is developmentally inappropriate based on any standards. However, electrons are referred to in the later unit on electricity, so giving minimal attention to atomic structure—without expecting any in-depth understanding—can be justified.

In the textbook, there is an attempt to use a lot of concrete experiments and several types of models to help students understand the relatively abstract concepts related to the particle nature of matter. Even with this approach, many middle school students will still—as mentioned in the standards and benchmarks sections below—have great difficulties in differentiating between atoms, elements, compounds and molecules. The idea that particles are always in motion—especially particles vibrating in solids—is also very difficult for middle school students to truly comprehend. Middle school teachers should therefore have realistic expectations about the extent to which students will understand the material in this unit.

From the National Science Education Standards:
“Students usually bring some vocabulary and primitive notions of atomicity to the science class but often lack understanding of the evidence and the logical arguments that support the particulate model of matter. Their early ideas are that the particles have the same properties as the parent material; that is, they are a tiny piece of the substance. It can be tempting to introduce atoms and molecules or improve students' understanding of them so that particles can be used as an explanation for the properties of elements and compounds. However, use of such terminology is premature for these students and can distract from the understanding that can be gained from focusing on the observation and description of macroscopic features of substances and of physical and chemical reactions. At this level, elements and compounds can be defined operationally from their chemical characteristics, but few students can comprehend the idea of atomic and molecular particles.”

From the Benchmarks for Science Literacy:
“The structure of matter is difficult for this grade span. Historically, much of the evidence and reasoning used in developing atomic/molecular theory was complicated and abstract. In traditional curricula too, very difficult ideas have been offered to children before most of them had any chance of understanding. The law of definite proportions in chemical combinations, so obvious when atoms (and proportions) are well understood, is not likely to be helpful at this level. The behavior of gases—such as their compressibility and their expansion with temperature—may be investigated for qualitative explanation; but the mathematics of quantitative gas laws is likely to be more confusing than helpful to most students. When students first begin to understand atoms, they cannot confidently make the distinction between atoms and molecules or make distinctions that depend upon it—among elements, mixtures, and compounds, or between "chemical" and "physical" changes. An understanding of how things happen on the atomic level—making and breaking bonds—is more important than memorizing the official definitions (which are not so clear in modern chemistry anyway). Definitions can, of course, be memorized with no understanding at all.

Going into details of the structure of the atom is unnecessary at this level, and holding back makes sense. By the end of the 8th grade, students should have sufficient grasp of the general idea that a wide variety of phenomena can be explained by alternative arrangements of vast numbers of invisibly tiny, moving parts.

To that end, students should become familiar with characteristics of different states of matter—now including gases—and transitions between them. Most important, students should see a great many examples of reactions between substances that produce new substances very different from the reactants. Then they can begin to absorb the rudiments of atomic/molecular theory, being helped to see that the value of the notion of atoms lies in the explanations it provides for a wide variety of behavior of matter. Each new aspect of the theory should be developed as an explanation for some observed phenomenon and grasped fairly well before going on to the next.”

Activity List

Lesson 1 (4:1) Exponents (Text pp. 76-80)
Lesson 2 (4:2) Observation, Inference, Models (Text pp. 81-84)
Lesson 3 (5:1) Case for Particles (Text pp. 88-91)
Lesson 4 (5:2) Hidden Structure of Matter (Text pp. 92-98)
Lesson 5 (5:3) Size of Particles (Text pp. 99-102)
Lesson 6 (5:4) Solids, Liquids, and Gases (Text pp. 103-104)
Lesson 7 (6:1) Temperature and Particles (Text pp. 107-110)
Lesson 8 (6:2) Changes of State (Text pp. 111-114)
Lesson 9 (6:3) Absorbing and Releasing Heat (Text pp. 115-118)
Lesson 10 (6:4) Particles: Mass and Volume (Text pp. 119-123)
Lesson 11 (7:1) Picturing an Atom (Text pp. 126-129)
Lesson 12 (7:2) Atomic Structure (Text pp 130-135)

Learning Objectives

Observe that the sizes of objects can be compared using an exponential scale.
Explain how exponential form is used to express very large and very small numbers.
Explain that observations are supported by facts.
Explain that inferences are supported by circumstantial evidence.
Examine models as representations of events or objects in the real world that can be used to test hypotheses.
Examine the evidence for the particle nature of matter.
Develop a model to explain observations of dissolving and the pouring and mixing of substances.
Explain that all matter is composed of atoms.
Recognize that there are a finite number of naturally occurring elements.
Demonstrate that all atoms of the same elements have the same properties.
Explain Explain that atoms combine to form molecules.
Identify molecules of different kinds of atoms as compounds.
Demonstrate that the molecules of different substances have different sizes.
Determine that atoms and molecules are extremely small.
Examine how some materials allow certain substances to pass through while blocking others.
Explain that the particles of matter are in constant motion.
Demonstrate that gas particles are farther apart than are the particles of liquids and solids.
Explain that heating a substance causes the particles of the substance to mover faster and farther apart.
Demonstrate that cooling matter causes the particles of matter to slow down and move closer together.
Explain that air expands when it is heated.
Recognize that not all substances expand and contract at the same rate.
Demonstrate that melting and freezing are the result of heat energy being added to or taken away from a substance.
Explain that the temperature remains constant at a substance's melting point or freezing point until all of the mater has either melted or frozen.
Define endothermic and exothermic charges.
Demonstrate that a charge of state requires substances to absorb or release heat energy.
Construct wet-bulb thermometers to study the process of evaporative cooling.
Investigate the three methods for determining the volume of small solid objects.
Demonstrate that different materials with the same volume may have different masses.
Explain that the mass of a given volume of a substance is an identifiable property of that substance.
Investigate Dalton's theory of matter, which states that all matter is made up of atoms.
Investigate Thomson's refinement of the atomic theory, which states that the atom contains both a positive and a negative charge.
Identify the parts of the atom.
Investigate Rutherford's discovery of a positively charged nucleus.
Investigate Bohr's planetary model of the atom.
Discuss the relative size protons, neutrons, and electrons.

Standards

Illinois Learning Standards (Middle School) As a result of their schooling students will be able to:

12. Know and apply concepts that describe properties of matter and energy and the interactions between them:

12.C.3a Explain interactions of energy with matter including changes of state and conservation of mass and energy
12.C.3b Model and describe the chemical and physical characteristics of matter (e.g., atoms, molecules, elements, compounds, mixtures).

11. Know and apply the concepts, principles and processes of scientific inquiry:

11.A.3a Formulate hypotheses that can be tested by collecting data.
11.A.3b Conduct scientific experiments that control all but one variable.
11.A.3c Collect and record data accurately using consistent measuring and recording techniques and media.
11.A.3d Explain the existence of unexpected results in a data set.
11.A.3e Use data manipulation tools and quantitative (e.g., mean, mode, simple equations) and representational methods (e.g., simulations, image processing) to analyze measurements.
11.A.3f Interpret and represent results of analysis to produce findings.
11.A.3g Report and display the process and results of a scientific investigation.

Illinois Science Assessment Framework (7^th Grade)

12.7.39	Understand that the phases of matter depend on how the atoms and molecules of a substance move.
12.7.40	Identify the most familiar elements which are gases at room temperature.
12.7.41	Know the definitions of melting point and boiling point and understand the concepts of evaporation and sublimation.
12.7.44	Define element as a substance that cannot be broken down into simpler substances by chemical interactions. Understand that there are over 100 known elements that combine in many ways to form many kinds of compounds.
12.7.46	Identify simple compounds (e.g., H2O).
12.7.47	Identify the atom as the smallest part of an element that still has the properties of that element
12.7.48	Identify the 3 subatomic building blocks, namely the electron, proton, and neutron. Know that the electron has a negative charge, the proton has a positive charge, and the neutron is electrically neutral
12.7.49	Understand that a molecule is two or more atoms joined by bonds. Understand that it is possible to have a molecule of an element, if the atoms are all of the same element, or a molecule of a compound, if the atoms in it are of different elements.
12.7.50	Identify the number of different kinds of elements in a chemical formula. Understand that water is a chemical compound, and that its formula is H2O.
12.7.51	Understand that during a chemical change atoms are neither created nor destroyed, but are rearranged to make new substances.
12.7.55	Understand that heat moves in predictable ways, flowing from warmer objects to cooler ones, until both reach the same temperature (thermal equilibrium)

Benchmarks for Science Literacy By the end of 8^th grade, students should know that:

All matter is made up of atoms, which are far too small to see directly through a microscope. The atoms of any element are alike but are different from atoms of other elements. Atoms may stick together in well-defined molecules or may be packed together in large arrays. Different arrangements of atoms into groups compose all substances.
Equal volumes of different substances usually have different weights.
Atoms and molecules are perpetually in motion. Increased temperature means greater average energy, so most substances expand when heated. In solids, the atoms are closely locked in position and can only vibrate. In liquids, the atoms or molecules have higher energy, are more loosely connected, and can slide past one another; some molecules may get enough energy to escape into a gas. In gases, the atoms or molecules have still more energy and are free of one another except during occasional collisions.
Scientific ideas about elements were borrowed from some Greek philosophers of 2,000 years earlier, who believed that everything was made from four basic substances: air, earth, fire, and water. It was the combinations of these "elements" in different proportions that gave other substances their observable properties. The Greeks were wrong about those four, but now over 100 different elements have been identified, some rare and some plentiful, out of which everything is made. Because most elements tend to combine with others, few elements are found in their pure form.

National Science Education Standards
Properties and Changes of Properties in Matter

A substance has characteristic properties, such as density, a boiling point and solubility, all of which are independent of the amount of the sample. A mixture of substances often can be separated into the original substances using one or more of the characteristic properties.
Substances react chemically in characteristic ways with other substances to form new substances to form new substances (compounds) with different characteristic properties. In chemical reactions, the total mass is conserved. Substances often are placed in categories or groups if they react in similar ways; metal is an example of such a group.
Chemical elements do not break down during normal laboratory reactions involving such treatments as heating, exposure to electric current, or reaction with acids. There are more than 100 known elements that combine in a multitude of ways to produce compounds, with account for the living and nonliving substances that we encounter.

Transfer of Energy

Energy is a property of many substances and is associated with heat, light, electricity, mechanical motion, sound, nuclei, and the nature of a chemical. Energy is transferred in many ways.
Heat moves in predictable ways, flowing from warmer objects to cooler ones, until both reach the same temperature.
In most chemical and nuclear reactions, energy is transferred into or out of a system. Heat, light, mechanical motion, or electricity might all be involved in such transfers.

Resources

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