C H E M I S T R Y

Chapter 2Atoms, Molecules, and Ions

Variableproperties

Similarproperties

The same number of protons

Cannot be separated physically

Different compositions Same compositions

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Covalent Bond: Results when two atoms share several (usually two) electrons. Typically a nonmetal bonded to a nonmetalMolecule: The unit of matter that results when two or more atoms are joined by covalent bonds.

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Insert Figure 2.12 p56

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Ionic Bond: A transfer of one or more electrons from one atom to another. A strong electrical attraction between charged particles. Typically a metal bonded to a nonmetal.

Ion: A charged particle

Cation: A positively charged particle. Metals tend to form cations.

Anion: A negatively charged particle. Nonmetals tend to form anions.

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Na1+ + Cl1-Na + Cl

11 protons10 electrons

17 protons18 electrons

11 protons11 electrons

17 protons17 electrons

In the formation of sodium chloride, one electron is transferred from the sodium atom to the chlorine atom.

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1+ 2+ 3+

Cation Charges for Typical Main-Group Ions

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Chapter 2/8

1-

Anion Charges for Typical Main-Group Ions

3- 2-

Naming Ionic Compounds

To name a compound that contains two elements,

• identify the cation and anion.

• name the cation first, followed by the name of the anion with an –ide ending.

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Ionic Compound: A neutral compound in which the total number of positive charges must equal the total number of negative charges.

Total positive charge = Total negative charge

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Some transition metals form more than one cation

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Use Roman numerals in parentheses to indicate the charge on metals that form more than one kind of cation.

lead(II) fluoride: PbF2Pb2+ F-

iron(III) oxide: Fe2O3Fe3+ O2-

tin(II) chloride: SnCl2Sn2+ Cl-

Binary Ionic Compounds

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ExampleWrite the formula and names of the following

compounds:

1) K+ and Br-

2) Al3+ and O2-

3) Pb4+ and S2-

4) Cu2+ and F-

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Because nonmetals often combine with one another in different proportions to form different compounds, numerical prefixes are usually included in the names of binary molecular compounds.

Binary Molecular Compounds

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N2F4

The second element listed is more anionlike and takes the name of the element with an “ide” modification to the ending.

The first element listed is more cationlike and takes the name of the element.

The prefix is added to the front of each to indicate the number of each atom.

dinitrogen tetrafluoride

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Binary Molecular Compounds

dinitrogen tetroxideN2O4

carbon monoxideCO

Whenever the prefix for the first element is “mono,” drop it.

Whenever the prefix ends in “a” or “o” and the element name begins with a vowel, drop the “a” or “o” in the prefix.

carbon dioxideCO2

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Learning CheckWrite the name of each covalent compound.

P2O5 _____________________

SiCl4 _____________________

CCl4 _____________________

N2O _____________________

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memorize

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Learning CheckWrite formula and name of the following

compounds:

A. Mg2+ and NO3-

B. Al3+ and BrO4-

C. Fe2+ and HSO4-

D. Ba2+ and PO33-

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ExamplesWrite the correct formula for each.

A. aluminum nitrate

B. copper(II) nitrate

C. iron(III) hydrogen sulfite

D. tin(IV) hydroxide

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