5.2-5.5

Polyatomic Ions • Chlorate

• Carbonate

• Phosphate

• Ammonium

• Acetate

• Iodate

• Nitrate

• Cyanide

• Bicarbonate

• Sulfate

• Hydroxide

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Formulas Describe Compounds

A compound is a distinct substance that is composed of atoms of two or more elements

Describe the compound by describing the number and type of each atom in the simplest unit of the compound› Molecules or ions

Each element is represented by its letter symbol

The number of atoms of each element is written as a subscript› If there is only one atom, the 1 subscript is not written

Polyatomic groups are placed in parentheses › Polyatomic ions come as packages!!! › If more than one

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Practice—Determine the Total Number of Atoms or Ions in One Formula Unit of Each of the Following.

Mg(C2H3O2)2

(Hg2)3(PO4)2

1 Mg + 4 C + 6 H + 4 O = 15

6 Hg + 2 P + 8 O = 16

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Classifying Materials Atomic elements = Elements

whose particles are single atoms Molecular elements(diatomic) =

Elements whose particles are multi-atom molecules

Molecular compounds = Compounds whose particles are molecules made of only nonmetals.

Ionic compounds = Compounds whose particles are cations and anions.

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Molecular Elements Certain elements occur as diatomic

molecules. 7 diatomic elements—The Rule of 7s

› The seventh element is H2. H O N F Cl Br I

H2

Cl2

Br2

I2

7N2 O2 F2

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Molecular Compounds Two or more

nonmetals

Smallest unit is a molecule

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Ionic Compounds

Metals + nonmetals

No individual molecule units, instead have a 3-dimensional array of cations and anions made of formula units.

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Classify Each of the Following as Either an Atomic Element, Molecular Element, Molecular Compound, or Ionic Compound.

Aluminum, Al

Aluminum chloride, AlCl3

Chlorine, Cl2

Acetone, C3H6O

Carbon monoxide, CO

Cobalt, Co

Ionic vs. Covalent Com

pounds

IONICCOVALENT

Formed from two ions

Consists of a METAL and a nonmetal or polyatomic ion

Formed from two NONMETALS

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Ionic Compounds Ionic compounds are made of ions. Ionic compounds always contain cations

and anions› Cations = + charged ions; anions = − charged

ions. The sum of the + charges of the cations

must equal the sum of the − charges of the anions

The overall charge of a compound is ZERO!!

Writing Formulas for IONIC Compounds

1. Write the elemental symbol for each element

2. Write the charges for each element (How do I figure this out?)

3. The total charge of all compounds equal ZERO!!!

Example Magnesium Fluoride

Ammonium Sulfide

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Practice—What Are the Formulas for Compounds Made from the Following Ions?

Potassium ion with a nitride ion.

Calcium ion with a bromide ion.

Aluminum ion with a sulfide ion.