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Chemical Bonds

Chapter 22

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Forming Chemical Bonds

o The force that holds two atomstogether is called a chemicalbond.

o Chemical bonds may form by theattraction between a positivenucleus and negative electrons

or the attraction between apositive ion and a negative ion

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Review

o Valence electrons are the electrons in theoutermost energy level. These sameelectrons are involved in the formation of

chemical bonds between two atoms

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Formation of Positive Ions

o A positive ion forms when an atomloses one or more valenceelectrons in order to attain a noblegas configuration

o

o

Positively

charged ionis called a

cation

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Transition Metals

o When forming positive ions, transitionmetals commonly lose theirvalence electrons, forming 2+ ions.n However, it is also possible for d

electrons to be lost

o A useful rule of thumb for these

metals is that they form ions with a2+ or 3+ charge.

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Formation of Negative Ions

o Nonmetals have a great attraction forelectrons and form stable outerelectron configuration by gainingelectrons

Negatively

charged ionis called ananion

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Checkpoint

Why do ions form?

Describe the formation of positive andnegative ions.

Predict the change that must occur toachieve noble gas stability Nitrogen

Sulfur Barium

Lithium

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Answers

Atoms gain stability by losing or gainingelectrons

Positive ions form when atoms lose valence

electronsn Negative ions form when valence electrons

are added to an atom

Nitrogen- gain 3 electrons (N3-)

Sulfur- gain 2 electrons (S

2-

) Barium- lose 2 electrons (Ba2+)

Lithium- lose 1 electron (Li1+)

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The Formation and Nature of Ionic

Bonds

o The electrostatic forcethat holds oppositelycharged particlestogether in an ionic

compound is referredto as an ionic bond

o Ionic bonds form betweencations (+) and anions(-)

oBinary compounds containtwo different elements

n Metallic cation

n Nonmetallic anionElectrons gained = electrons lost

OVERALL CHARGE OF THE COMPOUND FORMED MUST BE ZERO!!!

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The Formation and Nature ofCovalent Bonds

o Atoms of nonmetals are unlikely to gain or losee- therefore they share e- to attain noblegas stability.

o Single covalent bonds share 1 pair of e-o Double covalent bonds share 2 pairs of e-

o Triple covalent bonds share 3 pairs of e-

o Covalent bonds are formed betweennonmetal elements only!

http://static.newworldencyclopedia.org/d/d9/Covalent.pnghttp://static.newworldencyclopedia.org/d/d9/Covalent.png

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Comparing Ionic & Covalent

Bonds

Ionic CompoundsCrystalline solids(made of ions)High melting andboiling pointsConduct electricitywhen meltedMany soluble inwater but not in

nonpolar liquid

Covalent CompoundsGases, liquids, or solids (made ofmolecules)Low melting and boiling points

Poor electrical conductors in allphasesMany soluble in nonpolar liquidsbut not in water

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CW

o Pg 702 #s 1-6

o Pg 711 Modeling Chemical Bonding