Core Science Curriculum Framework and Grade-Level Concepts
6.1.a. Mixtures are made of combinations of elements and/or compounds, and they can be separated by using a variety of physical means.
Students should understand that…
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Everything is made of matter. Matter has two fundamental properties: it has weight (mass) and it takes up space (volume).
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All matter has a variety of properties, some of which are characteristic of the substance. Characteristic properties do not depend on the amount of the substance (as mass and volume do). Properties such as magnetic attraction, conductivity, density, pH, boiling point and solubility are characteristic properties that can be used to identify substances.
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Solids, liquids or gases can be combined to form mixtures. In a mixture, each substance keeps its individual properties. In some mixtures, each of the components can be seen (for example, rocks, twigs, insects and leaves are visible components of soil); in other mixtures, the individual substances blend so well that they appear to be a single substance (for example, oxygen, nitrogen and carbon dioxide are mixed together to form air).
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Mixtures can be separated using different methods, depending on the physical properties of the component substances. Filtering, evaporating, floating/settling, dissolving, and using magnets are all methods for separating mixtures based on the properties of their components.
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Solutions are mixtures that appear to be single substances because particles have dissolved and spread evenly throughout the mixture. Not all separation methods are effective for separating the components of solutions.
6.1.b. Pure substances can be either elements or compounds, and they cannot be broken down by physical means.
Students should understand that…
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All matter is made of particles called atoms that are too small to be seen without special magnification. For example, a gold ring can be broken into smaller and smaller pieces until the pieces are no longer visible.
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All matter is made of different combinations of about 100 pure substances called elements. The smallest particle of an element is an atom. Iron is an example of an element that is made up of only iron atoms.
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Each element has distinct characteristic properties. The Periodic Table of Elements is used to organize elements based on properties such as their reactivity, state of matter, conductivity or density. Element names are represented by letter symbols on the Periodic Table.
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Some elements, such as iron (“Fe”) and aluminum (“Al”), are classified as
metals
because they have similar properties. Individual metallic elements have distinct characteristic properties (for example, sodium (“Na”) is a light, soft metal that is nonmagnetic, while iron is a magnetic metal that is denser than sodium and aluminum).
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Some elements, such as carbon (“C”), hydrogen (“H”), oxygen (“O”) and chlorine (“Cl”), are classified as
nonmetals
. Carbon is a nonmetal that occurs in several different forms (graphite, diamond, and coal), each of which has distinct properties. Hydrogen and oxygen are nonmetals that are similar in that they are both gases; however, each gas has distinct characteristic properties.
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Atoms can combine chemically to make a molecule of a new substance with new properties called a compound. A molecule is the smallest part of a compound and is made of atoms of different elements in specific amounts
.
Unlike mixtures, compounds cannot be separated using the physical properties of the component elements.
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Compounds have different properties than the individual elements of which they are made. For example, table salt (NaCl) is a compound with different characteristic properties than the elements sodium and chlorine from which it is made; water (H
2
0) is a compound with different characteristic properties than the elements hydrogen and oxygen from which it is made. Different amounts of the same elements can produce compounds with different properties (for example, water (H
2
0) and hydrogen peroxide (H
2
0
2
).
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In a chemical reaction, atoms can rearrange to form different molecules of new compounds. During photosynthesis, carbon dioxide (CO
2
) is taken in by green plants and combined with water (H
2
O). The carbon, hydrogen and oxygen atoms rearrange to make two new compounds: glucose (made of atoms of carbon, oxygen, and hydrogen) and oxygen gas (made of atoms of oxygen).
Grade-Level Expectations
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Distinguish between mass and density.
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Explain that density is a ration of mass to volume. Use density to identify elements or separate mixtures.
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Demonstrate that different substances float or sink in water depending on their density.
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Compare and contrast the properties of metals, nonmetals, and metalloids.
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Differentiate between a mixture and an element or a compound and identify examples.
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Conduct and report on an investigation that uses physical means such as particle size, density, solubility, or magnetism to separate substances in a mixture.
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Compare and contrast physical and chemical changes, and use evidence to support or refute a claim that a chemical reaction has occurred.