MS-PS1 Matter and Its Interactions Key Ideas and Common Student Misconceptions This document compiles Key Ideas and developed by AAAS Project 2061 and the National Science Foundation. For additional information on this topic and others, check out: http://assessment.aaas.org/topics For similar instructional documents check out: www.sciencebrewer.org Atoms, Molecules, and States of Matter All matter is made up of atoms. All atoms are extremely small. All atoms and molecules are in constant motion. There are differences in the spacing, motion, and interaction of atoms and molecules that make up solids, liquids, and gases. For any single state of matter, increasing the temperature typically increases the distance between atoms or molecules. Therefore, most substances expand when heated. When heated, solids can change into liquids and liquids can change into gases. When cooled, gases can change into liquids and liquids can change into solids. These changes of state can be explained in terms of changes in the proximity, motion, and interaction of atoms and molecules. For any single state of matter, the average speed of the atoms or molecules increases as the temperature of a substance increases and decreases as the temperature of a substance decreases. Substances, Chemical Reactions, and Conservation of Matter A pure substance has characteristic properties, such as density, a boiling point, and solubility, all of which are independent of the amount of the substance and can be used to identify it. Many substances react chemically in predictable ways with other substances to form new substances with different characteristic properties. When substances interact to form new substances, the atoms that make up the molecules of the original substances rearrange into new molecules. Whenever substances within a closed system interact with one another, the total mass of the system remains the same. Whenever atoms interact with each other, regardless of how they are arranged or rearranged, the total mass stays the same.
1. Matter is anything that has mass and takes up space. 2. Matter includes all gases, liquids, and solids, which make up all living and non-living things. 3. Light and heat are not matter. 4. All matter solids, liquids, and gases is made up of discrete particles (atoms), rather than being continuous, and that these atoms are the matter rather than contained in matter. In other words, the atoms are not floating or embedded in some other substance, such as air or a liquid. 5. Matter can exist even when it cannot be seen. For example, gases or vapors are matter even though some of them cannot be seen. 6. Anything made up of atoms is matter. 7. It is because atoms take up space and have mass that all matter takes up space and has mass. Key Idea All matter is made up of atoms. Cells are not made up of atoms (Herrmann-Abell & DeBoer, 2008). Air does not take up space (Driver et al., 1994). 1. It is not expected that students will know about the internal structure of atoms or the existence of subatomic particles and, therefore, that these subatomic particles have mass. Atoms or molecules are embedded in matter (Renstrom et al., 1990; Griffiths et al., 1992; Lee et al., 1993; Johnson, 1998c). Solids are not made up of atoms; especially those without visible granularity (Johnson, 1998c; Nakhleh et al., 1999; Nakhleh et al., 2005; Nakhleh et al., 2006). Matter exists only when there is perceptual evidence of its existence (Stavy, 1990). Gases are not made up of atoms (AAAS Project 2061, n.d.).
1. Individual atoms are much smaller than things that can be seen and even much smaller than very small things, such as dust, germs and other microorganisms, blood cells, and plant cells. 2. This is true for all atoms. 3. All atoms are so small that billions of them make up these small things. Key Idea All atoms are extremely small. 1. The comparison with very small objects can be used to test students understanding of the relative size of atoms in relation to these objects. Students will not, however, be expected to know the actual size of atoms. A germ is smaller than an atom (AAAS Project 2061, n.d.). Cells are smaller than atoms (Tretter et al., 2006). A grain of sand is smaller than an atom (AAAS Project 2061, n.d.). Atoms/molecules are similar in size to cells, dust, or germs/bacteria (Lee et al., 1993; Nakhleh et al., 1999). The width of a hair is smaller than an atom (Tretter et al., 2006).
All atoms and molecules are in constant motion. 1. Atoms and molecules of all matter 1. Students are not expected to know the terms are always moving. rotation, translation, and vibration. 2. This is true for atoms or molecules of solids, 2. They are also not expected to know that liquids, and gases. atoms and molecules of different substances 3. Even when objects that are made up of these move at different speeds at the same atoms and molecules appear not to be temperature. moving, the atoms and molecules that make 3. Students are not expected to know the up those objects are nonetheless themselves special case of absolute zero temperature in constant motion. where, according to kinetic theory, there 4. The motion of atoms or molecules can should be no motion. include moving back and forth with respect to a fixed point, around a fixed point, and/or past each other from one fixed point to another. 5. The motion (speed and direction) of an atom or molecule can change when it undergoes collision with another atom or molecule resulting in one speeding up and the other slowing down. 6. Because atoms and molecules are continually colliding with each other, the atoms/molecules of the substance do not have the same speed. Atoms or molecules of a solid are not moving (Lee et al., 1993; Novak & Musonda, 1991). Molecules within a phase move at the same speed (Griffiths et al., 1992). The atoms or molecules of a liquid will stop moving when the liquid becomes a solid (Novak & Musonda, 1991). The atoms or molecules of a solid move only when heated. For example, the molecules of a glass window move only when the window is warmed by the sun (AAAS Project 2061, n.d.). Atoms or molecules of a liquid are not moving when the liquid itself is still (Johnson, 1998c). Atoms or molecules of a gas are not in motion (Novick et al., 1981). The atoms and molecules of a solid object move only when the object itself moves or is moved (AAAS Pilot testing, 2006).
There are differences in the spacing, motion, and interaction of atoms and molecules that make up solids, liquids, and gases. 1. The particles of a gas (atoms or molecules) are much farther apart than the atoms or molecules of a liquid or a solid. Because atoms or molecules of a gas are so far apart they rarely come in contact with each other. In solids and liquids, the atoms or molecules are packed closely together. 2. Although the motion of atoms or molecules of a solid is severely restricted, the atoms or molecules are constantly moving back and forth in all directions with respect to a fixed position. In liquids, the motion of the atoms or molecules is limited but the atoms or molecules can still move rapidly back and forth with respect to a fixed point, around a fixed point, and past each other from one fixed point to another. Atoms or molecules of a gas move freely and spread out throughout the container they occupy. 3. Similar to the pushes and pulls between magnets, atoms or molecules also push and pull on each other. a. In solids, the atoms or molecules pull strongly on each other and are linked together in rigid structures. b. In liquids, the atoms or molecules pull less strongly on each other, are more loosely connected, and form less rigid structures. c. In gases, the pull between atoms or molecules is so weak that they do not form structures. 4. Hardness, flow, and compressibility are macroscopic properties for which students are expected to know the molecular reason. a. Solids are hard because the atoms or molecules are linked together tightly in rigid structures, not because the individual atoms or molecules are hard. b. The atoms or molecules of liquids can easily move past each other from one fixed point to another but do not move apart from one another and 1. Students are not expected to know the nature of the bonds between atoms or between molecules. 2. They are not expected to know that atoms or molecules of a solid can sometimes move past each other. 3. Students are not expected to know the terms rotation, translation, and vibration. 4. They are not expected to know that plasma is a distinct state of matter, and they are not expected to know the properties of a plasma.
that this is why liquids flow and take the shape of their container but solids do not. c. Gases can be compressed because the atoms or molecules are not as close together as they could be, not because the individual atoms or molecules are soft. Atoms or molecules of a solid are not moving (Lee et al., 1993; Novak & Musonda, 1991). Particles of a gas are closely packed with no empty space between them (Benson et al., 1993; Novick & Nussbaum, 1978). Atoms and molecules of a gas in a container are not uniformly distributed (Novick et al., 1981; Lee et al., 1993). The gas state of a substance weighs less than the liquid or solid state (Stavy, 1990). Observable properties of the state are attributed to the individual molecules (e.g., molecules in a solid are hard; molecules move in gases and liquids, but not in solids; or the molecules of the substance change from soft to hard when a liquid freezes) (Lee et al., 1993). The molecules of the gas state are the lightest and the molecules of the solid state are the heaviest (Griffiths et al., 1992). Atoms or molecules of a gas are not in motion (Novick et al., 1981).
For any single state of matter, the average speed of the atoms or molecules increases as the temperature of a substance increases and decreases as the temperature of a substance decreases. 1. The temperature of a substance is directly related to the average speed of its atoms/molecules. 2. Therefore, as matter in any particular state is heated, stirred, shaken, etc., the average speed of its atoms/molecules increases, which is reflected in an increase in its temperature. 3. As matter in any particular state cools, the average speed of its atoms/molecules decreases, which is reflected in a decrease in its temperature. 4. When the temperature of matter in any particular state remains constant, the average speed of its atoms/molecules remains constant, and when the average speed of the atoms/molecules of matter in any particular state remains constant, the temperature of the matter remains constant. 1. Students are not expected to know that temperature remains constant during a change of state, which is a later idea. 2. They are not expected to know the term kinetic energy or that kinetic energy is a function of mass and velocity. 3. Students are also not expected to know that atoms and molecules of different substances move at different speeds at the same temperature. 4. They are not expected to know that increasing pressure will increase the temperature or any other application of the gas law equations. 5. Students are also not expected to know the special case of absolute zero temperature where, according to kinetic theory, there should be no motion. Increasing the speed of the atoms or molecules of a substance does not change the temperature of the substance (AAAS Project 2061, n.d.). The average speed of the atoms or molecules of a substance decreases when the temperature increases and increases when the temperature decreases (AAAS Project 2061, n.d.). Atoms or molecules of a solid are not moving (Lee et al., 1993; Novak & Musonda, 1991). Atoms or molecules of a liquid in a sealed container will stop moving (AAAS Project 2061, n.d.). The average speed of the atoms or molecules of a substance remains the same with a change in temperature (AAAS Project 2061, n.d.).
For any single state of matter, increasing the temperature typically increases the distance between atoms or molecules. Therefore, most substances expand when heated. 1. As the temperature of a substance increases, the average distance between the atoms/molecules of the substance typically increases, causing the substance to expand. 2. As the temperature of a substance decreases, the average distance between the atoms/molecules typically decreases, causing the substance to contract. 3. This expansion or contraction can happen to solids, liquids, and gases. 4. Expansion or contraction due to changes in temperature can also happen to mixtures of substances. 5. Expansion or contraction due to changes in temperature is not permanent (e.g., objects that expand when heated then contract when cooled). 6. The number of atoms and the mass of the atoms do not change with changes in temperature. 7. Different substances expand and contract differently. 1. Students are not expected to know the details of the relationship between the speed of the atoms or molecules and thermal expansion. 2. They are also not expected to know the substances that violate this rule and shrink when heated or that water will shrink when heated anywhere between 0 C and 4 C. 3. Students are not expected to know or apply gas law equations. 4. Because the definition of the size of an atom is varied and complex, we only expect students to know that the size of an atom or molecule does not decrease when the temperature increases and that the size does not increase when temperature decreases. Solid substances do not expand or contract with changes in temperature (Herrmann-Abell & DeBoer, 2007, 2008). The mass of the atoms or molecules of a substance increases when the temperature increases and decreases when the temperature decreases (AAAS Project 2061, n.d.). The average distance between the atoms or molecules of a substance remains the same when the temperature of the substance changes (AAAS Project 2061, n.d.). Heat is made of "heat molecules" (Berkheimer et al., 1988). The number of atoms or molecules of a substance increases when the temperature increases and decreases when the temperature decreases (Herrmann-Abell & DeBoer, 2008). Water molecules break down when heated (Griffiths et al., 1992). The mass of the atoms or molecules of a substance increases when the temperature decreases and decreases when the temperature increases (Herrmann-Abell & DeBoer, 2007, 2008). The molecules of air break down when the air is cooled (AAAS Project 2061, n.d.). Substances shrink when heated (especially solids) (Lee et al., 1993). The number of atoms or molecules of a substance increases when the temperature decreases and decreases when the temperature increases (Herrmann-Abell & DeBoer, 2007). The size of the atoms or molecules of a substance increases when the temperature decreases and decreases when the temperature increases (AAAS Project 2061, n.d.).
When heated, solids can change into liquids and liquids can change into gases. When cooled, gases can change into liquids and liquids can change into solids. These changes of state can be explained in terms of changes in the proximity, motion, and interaction of atoms and molecules. 1. When the temperature of a liquid decreases, the average speed of the atoms or molecules decreases and, as a result, the pull that exists between the atoms or molecules is strong enough to link them together as a solid. 2. When the temperature of a solid increases, the average speed of the atoms or molecules increases and the pull between the atoms or molecules is no longer strong enough to hold them together as a solid; the atoms or molecules are now more loosely connected as a liquid. 3. When the temperature of a gas decreases, the average speed of the atoms or molecules decreases and, as a result, the pull that exists between the atoms or molecules is strong enough to loosely connect them together as a liquid. 4. When the temperature of a liquid increases, the average speed of the atoms or molecules increases and the pull between the atoms or molecules is no longer strong enough to hold them together as a liquid. In this case, the pull between atoms or molecules is so weak that they are no longer connected to each other, but rather they exist as a gas. 5. At the boiling point and freezing point, atoms or molecules from anywhere in the substance can enter the gas state and solid state, respectively. Because of this, the bubbles that form when the substance is boiling are atoms or molecules of that substance in the gaseous state. 6. Evaporation or condensation can also occur independent of temperature; i.e., at any temperature there are some atoms or molecules that may move from one state to another at the surface of a substance. This also includes atoms or molecules on the surface of a solid that can enter the gas state. 7. A substance is made up of the same type of atom or molecule regardless of whether it is in the solid, liquid, or gas state. There 1. Although changes of state can be caused by changes in either temperature or pressure, students are only expected to know the effects of changes in temperature.
is no change in the identity of the atoms or molecules during a change of state; only the arrangement, motion, and interaction of the atoms or molecules change. 8. Atoms or molecules are not destroyed during a change of state. 9. Any change of state is reversible. The molecules of a substance break down into individual atoms when the substance evaporates. During evaporation, water breaks down into hydrogen and oxygen (Bar et al., 1991; Bar et al., 1994). The molecules of a substance break down into individual atoms when the substance boils. For example, molecules of water become atoms of hydrogen and oxygen when water boils (Osborne et al., 1983; Renstrom et al., 1990). When water boils, the bubbles formed during boiling contain air, not water in the gas state (Osborne et al., 1983; Renstrom et al., 1990; Bar et al., 1991; Johnson, 1998a; Chang, 1999). Heat is made of "heat molecules" (Berkheimer et al., 1988). Molecules change shape during a phase change (Novak et al., 1991; Griffiths et al., 1992). Observable properties of the state are attributed to the individual molecules (e.g., molecules in a solid are hard; molecules move in gases and liquids, but not in solids; or the molecules of the substance change from soft to hard when a liquid freezes) (Lee et al., 1993). The identity of the molecules of a substance changes during a phase change (Lee et al., 1993). Molecules change weight/mass during a phase change (Griffiths et al., 1992). Matter is destroyed during melting (AAAS Project 2061, n.d.). Molecules change size during a phase change (Novak et al., 1991; Griffiths et al., 1992). Matter is destroyed during boiling (AAAS Project 2061, n.d.). Matter is destroyed during evaporation (Bar & Galili, 1994; Bar & Travis, 1991; Lee et al., 1993; Osborne & Cosgrove, 1983) When water evaporates from an object, that water is absorbed into the object (Osborne et al., 1983; Bar et al., 1991; Bar et al., 1994).
A pure substance has characteristic properties, such as density, a boiling point, and solubility, all of which are independent of the amount of the substance and can be used to identify it. 1. Note: The term characteristic property is used to emphasize that these properties are defining attributes that are independent of the amount of the sample, regardless of time, location, size, or shape. 2. The term substance means a pure material that is made of the same matter throughout. This is in contrast to the common definition that equates substance with matter that could be made of either a single substance or a mixture of more than one substance. To make this explicit, the phrase pure substance is used in assessment items. 3. A substance can be a solid, a liquid, or a gas. 4. Every substance has a set of characteristic properties that are always the same for that substance, regardless of time, location, shape, or size. 5. Furthermore, characteristic properties are consistent throughout a sample of a substance. 6. Characteristic properties with which students should be familiar are boiling point, melting and freezing point, solubility (i.e. how much of the substance can dissolve in water), flammability (i.e. the ease with which a substance will catch on fire), odor, color, and density (i.e., that equal volumes of different substances have different masses). 7. Weight, mass, volume, shape, length/width, texture, and temperature are not characteristic properties of substances and may change. 8. The characteristic properties of a substance do not change when temperature and pressure remain the same. 9. No two substances can have the same set of characteristic properties under the same conditions and that if two materials have even one different characteristic property, they are different substances. 1. Students are not expected to know that the properties of substance can be different at the nanoscale. 2. They are not expected to know the formula for density (density = mass/volume). 3. Students are not expected to know that the atomic mass of a substance is a characteristic property. 4. They are not expected to know whether specific materials are or are not pure substances. 5. Because some properties do change with changing conditions (e.g., changing atmospheric pressure affects boiling point) all assessment items will make comparisons between substances where it is clear that the conditions, such as temperature and pressure, are constant.
If two substances share one characteristic property, they are the same substance (AAAS Project 2061, n.d.). The melting point of a substance is dependent on the amount of substance. For example, the melting point of a ball of wax will change if a piece of wax is removed from the ball (AAAS Project 2061, n.d.). Melting point is not a characteristic property of a pure substance. Volume is a characteristic property of a substance (DeBoer et al., 2009). Color is not a characteristic property of a pure substance (AAAS Project 2061, n.d.). Boiling point is not a characteristic property of a pure substance. Density is not a characteristic property of a pure substance. If most of the listed characteristic properties are the same, the substances are the same (AAAS Project 2061, n.d.). Temperature is a characteristic property of the substance (Thomaz et al., 1995). Mass/weight is a characteristic property of a substance (DeBoer et al., 2009). Freezing point is not a characteristic property of a pure substance. Flammability is not a characteristic property of a pure substance. Shape is a characteristic property of a substance (AAAS Project 2061, n.d.). Length is a characteristic property of a substance (AAAS Project 2061, n.d.). Width is a characteristic property of a substance (AAAS Project 2061, n.d.).
Many substances react chemically in predictable ways with other substances to form new substances with different characteristic properties. 1. When substances react chemically one or more new substances are formed. 2. If a new substance does not appear, a chemical reaction did not occur. 3. The products of a chemical reaction can be identified as new substances because each product has different characteristic properties from the original substances under the same conditions. 4. Liquids, solids, or gases can be reactants or products in chemical reactions. 5. It is possible for a single substance to undergo a chemical reaction, such as when the substance is heated or an electrical current flows through the substance. 6. It is not true that all chemical reactions are irreversible. 7. Students are not expected to know that chemical reactions involve the rearrangement of atoms into new molecules. This idea is addressed in a later idea (Idea D). 8. Students are also not expected to know that nuclear reactions are not chemical reactions nor why nuclear reactions are not chemical reactions. Nuclear reactions are addressed in later ideas (4E/H6* and 4G/H6*) 9. By predictable ways, we mean that the same products will be formed when the same reactants are combined regardless of location and experimental set-up. Students are not expected to predict what the products of a reaction will be. 10. Students are expected to know that the original substances in a chemical reaction are called reactants and the resulting substances are called products but they will not be assessed on these definitions. Chemical reactions involve two reactants (Cavallo et al., 2003; Eilks et al., 2007). A chemical change is irreversible (Cavallo et al., 2003; Calik et al., 2005). A chemical reaction occurs when a substance dissolves (Novak et al., 1991; BouJaoude, 1992; Abraham et al., 1994; Ahtee et al., 1998; Stavridou et al., 1998; Valanides, 2000; Eilks et al., 2007) A chemical reaction occurs during a change of state (Hall, 1973; Novak et al., 1991; BouJaoude, 1992; Ahtee et al., 1998; Stavridou et al., 1998). A chemical reaction always happens when two substances are combined together (AAAS Project 2061, n.d.). Chemical reactions involve only the production of gas (Cavallo et al., 2003). Chemical reactions involve liquids only (Cavallo et al., 2003). A chemical reaction always happens when two liquids are combined together (DeBoer et al., 2008). Chemical reactions occur between solids and liquids but not between solids and gases (AAAS Project 2061, n.d.). All chemical reactions are inherently dangerous (Cavallo et al., 2003). A solid substance is always formed during a chemical reaction (DeBoer et al., 2008). A chemical reaction must take place in a laboratory (Herrmann-Abell et al., 2009).
When substances interact to form new substances, the atoms that make up the molecules of the original substances rearrange into new molecules. 1. During a chemical reaction the atoms that are linked together in molecules (or arranged in other patterns such as arrays and crystals) rearrange to make new molecules. 2. If the atoms are not rearranged, then a chemical reaction has not occurred. 3. New substances are made of the same kinds of atoms as the original substances (i.e., the atoms themselves did not change during the reaction). 1. The idea that the number of each kind of atom stays the same will be assessed under Idea H (conservation of matter). 2. Students are not expected to know the term bond or how chemical bonds are formed or broken during chemical reactions. 3. They are not expected to know that during chemical reactions, atoms are not turned into energy. The atoms of the reactants of a chemical reaction are transformed into other atoms (Andersson, 1986). Substances can change their characteristic properties but maintain their identity (Pfundt, 1982). The products of a chemical reaction are the same substances as the reactants but with different properties (Solomonidou et al., 2000). The products of a chemical reaction, though unseen, must have somehow existed from the start in another location, such as in the air or inside the reactants (Andersson, 1986; Solomonidou et al., 2000). After a chemical reaction, the product is a mixture in which the old substances persist, and is not a new substance (Johnson, 2000b; Solomonidou & Stavridou, 2000). The reactants and products of a chemical reaction are different and independent of each other. There is no recognition of a change of one sample to the other (Johnson, 2000b).
Whenever substances within a closed system interact with one another, the total mass of the system remains the same. 1. When substances mix, undergo chemical reactions, change state, or dissolve, or when objects are cut or broken into smaller pieces, the total mass of all the matter will always remain the same. 2. Regardless of the form that the products of these processes may take (for example, when a sugar cube dissolves in water or a chemical reaction produces a gas), the mass will always stay the same. 3. If it appears that the mass has changed, it is because some material has not been accounted for. 4. Because light is not matter, its presence or absence does not affect the mass of the matter. 1. Students are not expected to know that mass is not conserved in energy-mass conversions such as nuclear reactions or other subatomic interactions. 2. Note: The words weight, weigh, and mass are used appropriately in the assessment items. The students are not expected to know the difference between weight and mass. Mass is not conserved during processes in which gases take part (Mas et al., 1987; Berkheimer et al., 1988; Hesse et al., 1992). If a gas is produced during a chemical reaction that takes place in a closed system, the total mass decreases (Ozmen et al., 2003). In a closed system, the total mass increases during a precipitation reaction (Barker et al., 1999; Ozmen et al., 2003). When a liquid in a closed container is heated, the mass of the liquid increases as the liquid expands (AAAS Project 2061, n.d.). During biological decomposition in a closed system, the total mass of the system decreases (Mitchell et al., 1984). In a closed system, mass decreases after a solid dissolves in a liquid (Stavy, 1990b; Ozmen et al., 2003). When a chemical reaction occurs, matter just disappears. For example, gasoline is used up in the car and disappears (Andersson, 1986). Mass increases after a solid dissolves in a liquid (Stavy, 1990b). Matter can disappear with repeated division, dissolving, evaporation, or chemical change (Smith et al., 2004).
Whenever atoms interact with each other, regardless of how they are arranged or rearranged, the total mass stays the same. 1. Atoms are not created or destroyed when substances mix, undergo chemical reactions, change state, or dissolve, or when objects are cut or broken into smaller pieces. 2. The total number of each kind of atom always remains the same regardless of what happens to the matter (mixing, chemical reactions, changes of state, dissolving, or objects being cut or broken into smaller pieces). 3. The mass of an atom does not change. 4. If the measured mass has changed, it is because some atoms have not been accounted for. 1. Students are not expected to know that mass is not conserved in energy-mass conversions such as nuclear reactions or other subatomic interactions. New atoms are created during chemical reactions (AAAS Project 2061, n.d.). Atoms can be destroyed during a chemical reaction (AAAS Project 2061, n.d.). Mass is not conserved during processes in which gases take part (Mas et al., 1987; Berkheimer et al., 1988; Hesse et al., 1992). If a gas is produced during a chemical reaction that takes place in a closed system, the total mass decreases (Ozmen et al., 2003). The mass of a closed system will increase if a new kind of molecule is formed in the system (AAAS Project 2061, n.d.). The number of different kinds of molecules, not the number of each kind of atom, is always conserved (AAAS Project 2061, n.d.). Atoms can become lighter during a chemical reaction (AAAS Project 2061, n.d.). The total number of atoms, not the number of each kind of atom, is always conserved (AAAS Project 2061, n.d.). The mass of a closed system will decrease if two substances combine to form one substance (AAAS Project 2061, n.d.). Atoms can become heavier during a chemical reaction (AAAS Project 2061, n.d.). The number of molecules is always conserved (Mitchell et al., 1984).