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Elements and Compounds

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Two Types of Substances

• One type of pure substance can be broken down into simpler substances. This type of substance is called a compound.

• Another type of substance cannot be broken down into simpler substances. Such a substance is called an element.

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• All the substances of the universe are either elements, compounds formed from elements, or mixtures of elements and compounds.

Two Types of Substances

• Of the known elements, only about 90 occur naturally on Earth. The remainder are synthesized, usually in barely detectable amounts, in high-energy nuclear experiments. • Less than half of the 90 naturally occurring elements are abundant enough to play a significant role in the chemistry of everyday stuff.

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Organizing the Elements

• The periodic table organizes elements in a way that provides a wealth of chemical information—much more than is evident to you now. It shows the chemical symbols for the elements.

• Their symbols usually correspond to their names in Latin.

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Periodic Table of the ElementsTopic 1Topic 1

Compounds Are More Than One Element

• A more complete definition is that a compound is a chemical combination of two or more different elements joined together in a fixed proportion with a unique set of chemical and physical properties.

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• More than 10 million compounds are known and the number keeps growing.

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• Some new compounds are discovered and isolated from natural chemical sources such as plants and colonies of bacteria and are synthesized in laboratories for many different uses.

Compounds Are More Than One Element

• The properties of the compound are different from the properties of the elements that compose the compound.

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silver + bromine = silver bromide

Compounds Are More Than One Element

• A formula is a combination of the chemical symbols that show what elements make up a compound and the number of atoms of each element.

Compound Formula

Caffeine C8H10N4O2

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Compounds Are More Than One Element

• Formulas provide a shorthand way of describing a submicroscopic view of a compound.

• You probably already use formulas like H2O and CO2 as a way of talking about water and carbon dioxide.

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HOMEWORK

•Pg. 33 Section Review Questions 1-5 (Copied on the back of item # 21)

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