Download - Lecture 2.3- Elements vs. Compounds
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Bellwork- Classify MatterIdentify 5 items that fit each of the following
categories.a) Substanceb) Homogeneous mixturec) Heterogeneous mixtured) Solution
Select one thing from category b and one from category c and outline a method for separating the components.
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Lecture 2.3- Elements vs. Compounds
Elements and compounds are both pure substances.
How are they different?
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An element is the simplest form of matter.
A compound is a substance that contains two or more elements chemically combined in a fixed proportion.
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Compounds can be broken down into simpler substances by chemical means, but elements cannot.
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Breaking Down Compounds
A chemical change produces matter with a different composition than the original matter.
When table sugar is heated, it goes through a series of chemical changes.
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The final products of these chemical changes are solid carbon and water vapor. The following diagram summarizes the process.
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Because sugar can be chemically broken into more than one element, it is a compound.
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Liquid H2O H2O vapor
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Liquid H2O H2O vapor
Physical change because it is still H2O!
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Liquid H2O H2O vapor
Physical change because it is still H2O!
Glass cup pile of broken glass
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Liquid H2O H2O vapor
Physical change because it is still H2O!
Glass cup pile of broken glass
Physical change because it is still glass!
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Liquid H2O H2O vapor
Physical change because it is still H2O!
Glass cup pile of broken glass
Physical change because it is still glass!
H2 + O2 H2O
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Liquid H2O H2O vapor
Physical change because it is still H2O!
Glass cup pile of broken glass
Physical change because it is still glass!
H2 + O2 H2O
Chemical change because H2 and O2 become something different.
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Properties of Compounds
The properties of compounds are very different from those of their component elements.
When the elements sodium and chlorine combine chemically to form sodium chloride, there is a change in composition and a change in properties.
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Chlorine is used to kill harmful organisms in swimming pools.
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Sodium is stored under oil to keep it from reacting with oxygen or water vapor in the air. Sodium vapor produces the light in some street lamps.
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Sodium Chloride (commonly known as table salt) is used to season or preserve food.
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Sodium Chloride (commonly known as table salt) is used to season or preserve food.
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Cl + Na NaCl
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Sodium Chloride (commonly known as table salt) is used to season or preserve food.
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Cl + Na NaClPoison explosive food!
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Sodium Chloride (commonly known as table salt) is used to season or preserve food.
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Cl + Na NaClPoison explosive food!element element compound
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This flowchart summarizes the process for classifying matter.
Figure 2.11 on page 50
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for Conceptual Problem 2.2
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Chemists use chemical symbols to represent elements, and chemical formulas to represent compounds.
These chemical symbols were used in earlier centuries.
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Each element is represented by a one or two-letter chemical symbol.
The first letter is always capitalized.
The 2nd letter (if applicable) is always lowercase
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1. Passing an electric current through a certain substance produces oxygen and sulfur. This substance cannot be a(n)
a. compound.
b. mixture.
c. element.
d. solution.
2.3 Section Quiz
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2. Which of the following is a mixture?
a. sodium chloride
b. carbon dioxide
c. sucrose
d. air
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3. The symbol for the element potassium is
a. K.
b. Po.
c. P.
d. Pt.
2.3 Section Quiz.