ch 22 chemical bonding
TRANSCRIPT
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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