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Chapter 8

Covalent Bonding I

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Molecules and Molecular Cpds

noble gases (e.g. He and Ne) and most elements are monatomic.

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Molecules and Molecular Cpds

• Non-metals• e.g. [O2 ;not a cpd], CO2, C6H12O6

element

Covalent cpds• atoms held together by sharing e- are joined by

a covalent bond to form covalent cpds

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Molecules and Molecular Cpds

Covalent bonds• not so strong as Ionic bonds (electrostatic

attractions).

• Covalent cpds: made up of ALL nonmetals (how about ionic cpds?)

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Molecules and Molecular Cpds

Molecule • a neutral group of atoms (all nonmetals) joined

together by covalent bonds.

• may be a cpd (e.g. CO2) or an element (e.g. N2)

covalent cpds = molecular cpds

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Molecules and Molecular Cpds

• e.g. air contains oxygen molecules (O2) and nitrogen molecules (N2)---not cpds

A diatomic element consists of 2 atoms. e.g. 7 diatomic elements are H2, N2, O2,

F2, Cl2, Br2, I2

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Diatomic Molecules

Hydrogen Colorless gas H2

Nitrogen Colorless gas N2

Oxygen Pale blue gas O2

Fluorine Pale yellow gas F2

Chlorine Pale green gas Cl2

Bromine Reddish brown liquid Br2

Iodine Lustrous, dark purple solid

I2

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A Hydrogen Molecule

• 2 H atoms share a pair of e- in a covalent bond.

A covalent bond is formed by 2 shared e-.

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Covalent Bonds

• 2 of the same atoms form a covalent bond, e.g., when 2 F atoms form the F2 molecule.

• a pair of valence e- are shared---single covalent bond (2 shared e-).

• Form octets of for both atoms

Shared pair of e-

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Molecules and Molecular Cpds

Molecular cpd (covalent cpd):

- cpds composed of molecules

• e.g. H2O , CO2 , C6H12O6

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Molecules and Molecular Cpds

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Physical Properties Properties Ionic cpd Covalent cpd

Example NaCl CO 2

State at room temperature Crystalline solid Solid, liquid or gas

Melting point High Low

Conduct electricity in liquid state

Yes No

Water solubility High Low

Conduct electricity in aqueous solution

Yes poor

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Molecular Formulas

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Covalent Bonds

• All diatomic elements (F2, Cl2, Br2, I2, O2, N2, and H2) have covalent bonds.

• are molecules (not molecular cpds)• The other molecules are ALL cpds

• Most of the elemental diatomic molecules are gases at room temp—Cl2, F2, O2, N2, and H2.

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Modeling Water

• 2 covalent bonds.

• octet• duplet

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Lone (unshared) pair

Bonding (shared) pair

3 covalent bonds

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A Model for Ammonia

• Each H shares a pair of e- with the N.

• N’s remaining 2 e- form a lone pair.

• N has a complete octet of e-.

Lone pair

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double bond

• sharing 2 pairs of e- between 2 atoms.

Modeling Carbon Dioxide

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Double Bonds and Triple bonds

F−F

O=O

N≡N

O=C=O

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(1) Name the elements in the order listed in the formula.

(2) Use prefixes to indicate the # of each kind of atom.

9.3Naming Binary Molecular Cpds

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(3) Omit the prefix mono- when the formula contains only 1 atom of the 1st element in the name. e.g. CO2 (we don’t say monocarbon)

(4) The suffix of the name of the 2nd element is -ide.

9.3Naming Binary Molecular Cpds

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(5) Use the prefixes in the name to tell the subscript of each element in the formula.

(6) Then write the correct symbols for the 2 elements with the appropriate subscripts.

9.3Writing Formulas for Binary Mol. Cpds

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9.3Naming Binary Molecular Cpds

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Naming Binary Molecular Cpds

NF3 SF4

CO2 SbCl3

CO NH3

H2O CF4

CS2 P4S3

BCl3 SO2

IF7 SO3

PCl5 CCl4

C2O5 MgCl2

HCl SiCl4

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CST problem 1

(picture of a circuit) The above picture shows a light bulb connected to a battery with the circuit interrupted by a solution. When dissolved in the water to form a 1.0 molar solution, all of the following substances will complete a circuit allowing the bulb to light except

A hydrochloric acid

B sodium nitrate

C sucrose

D ammonium sulfate

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Name Hydrogen Chlorine Ammonia Methane

Molecular Formula

H2 Cl2 NH3 CH4

CST problem 2

What type of bond do all of the molecules in the table above have in common?

A covalent

B ionic

C metallic

D polar

Table of common molecules

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The End