1 chapter 8 “covalent bonding” ball-and-stick model

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Chapter 8

“Covalent Bonding”

Ball-and-stick model

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Section 8.1Molecular Compounds

OBJECTIVES:

–Distinguish between the melting points and boiling points of molecular compounds and ionic compounds.

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Section 8.1Molecular Compounds

OBJECTIVES:

–Describe the information provided by a molecular formula.

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Bonds are…Bonds are… Forces that hold groups of Forces that hold groups of

atoms together atoms together and make them and make them function as a unit. Two types:function as a unit. Two types:

1)1) Ionic bondsIonic bonds – – transfertransfer of of electrons electrons (gained or lost; (gained or lost; makes makes formula unitformula unit))

2)2) Covalent bondsCovalent bonds – – sharingsharing of of electrons. electrons. The resulting The resulting particle is called a particle is called a ““moleculemolecule””

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Covalent BondsThe word covalent is a

combination of the prefix co- (from Latin com, meaning “with” or “together”), and the verb valere, meaning “to be strong”.

Two electrons shared together have the strength to hold two atoms together in a bond.

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MoleculesMolecules Many elements found in nature

are in the form of molecules: a neutral group of atoms joined

together by covalent bonds. For example, air contains oxygen For example, air contains oxygen

molecules, consisting of two molecules, consisting of two oxygen atoms joined covalentlyoxygen atoms joined covalently

Called a “Called a “diatomicdiatomic molecule” (O molecule” (O22))

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How does H2 form?

The nuclei repel each other, since they both have a positive charge (like charges repel).

++

(diatomic hydrogen molecule)

+ +

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How does H2 form?

++

But, the nuclei are attracted to the electrons

They share the electrons, and this is called a “covalent bond”, and involves only NONMETALS!

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Covalent bondsNonmetals hold on to their valence

electrons. They can’t give away electrons to bond.

–But still want noble gas configuration. Get it by sharing valence electrons with

each other = covalent bonding By sharing, both atoms get to count

the electrons toward a noble gas configuration.

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Covalent bonding Fluorine has seven valence

electrons (but would like to have 8)

F

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electrons A second atom also has seven

F F

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electrons A second atom also has seven By sharing electrons…

F F

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F F

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F F

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F F

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F F

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Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons…

…both end with full orbitals

F F

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Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons… …both end with full orbitals

F F8 Valence electrons

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Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons… …both end with full orbitals

F F8 Valence electrons

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Molecular Compounds Compounds that are bonded

covalently (like in water, or carbon dioxide) are called molecular compounds

Molecular compounds tend to have relatively lower melting and boiling points than ionic compounds – this is not as strong a bond as ionic

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Molecular Compounds Thus, molecular compounds tend to

be gases or liquids at room temperature

–Ionic compounds were solids A molecular compound has a

molecular formula:

–Shows how many atoms of each element a molecule contains

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Molecular Compounds The formula for water is written as

H2O–The subscript “2” behind hydrogen

means there are 2 atoms of hydrogen; if there is only one atom, the subscript 1 is omitted

Molecular formulas do not tell any information about the structure (the arrangement of the various atoms).

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- Page 215

These are some of the different ways to represent ammonia:

1. The molecular formula shows how many atoms of each element are present

2. The structural formula ALSO shows the arrangement of these atoms!

3. The ball and stick model is the BEST, because it shows a 3-dimensional arrangement.

1 chapter 8 “covalent bonding” ball-and-stick model

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