Lecture 2.3- Elements vs. Compounds

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.

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.

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





H2 + O2 H2O

Chemical change because H2 and O2 become something different.

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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Cl + Na NaCl


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Cl + Na NaClPoison explosive food!


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Cl + Na NaClPoison explosive food!element element compound

This flowchart summarizes the process for classifying matter.

Figure 2.11 on page 50

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for Conceptual Problem 2.2

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

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

2. Which of the following is a mixture?

a. sodium chloride

b. carbon dioxide

c. sucrose

d. air

2.3 Section Quiz

3. The symbol for the element potassium is

a. K.

b. Po.

c. P.

d. Pt.

2.3 Section Quiz.

Lecture 2.3- Elements vs. Compounds

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Transcript of Lecture 2.3- Elements vs. Compounds