review we can tell how many electrons and atom will gain or lose by looking at its valence. metals...
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REVIEWREVIEW• We can tell how many electrons and atom will gain
or lose by looking at its valence.
• Metals like to lose electrons. (Cations)– Ex. Na +
• Nonmetals like to gain electrons. (Anions)– Ex: O 2-
• All elements try to have a full valence of 8 electrons(OCTET RULE).
REVIEWREVIEW• Cation- is a positively charged ion.
• How do cations form?– When atoms LOSE electrons they become
positive.
• Anion- is a negatively charged ion.
• How do anions form?– When atoms GAIN electrons they become
negative.
Chemical Bonding NotesChemical Bonding Notes
A A chemical bondchemical bond is the force of attraction is the force of attraction that holds two atoms together.that holds two atoms together.
Attractive Force
Na Cl
• http://www.wisc-online.com/objects/ViewObject.aspx?ID=GCH2204
Why do elements form Why do elements form chemical bonds?chemical bonds?
Atoms form chemical bonds in order to fill Atoms form chemical bonds in order to fill their outermost energy level with electrons.their outermost energy level with electrons.
• A full valence shell causes an atom to be A full valence shell causes an atom to be more stable.more stable.•A full valence shell consists of 8 valence electrons.
Ionic BondingIonic Bonding
Ionic bondsIonic bonds: Metal atoms transfer electrons : Metal atoms transfer electrons to nonmetal atoms. Producing to nonmetal atoms. Producing oppositely charged ions oppositely charged ions
(cation & (cation & anion) which attract each anion) which attract each other.other.
Na + ClNa + Cl Na Na++ Cl Cl--
Remember: Non-metal atoms take electrons from metal Remember: Non-metal atoms take electrons from metal atoms to form an octet.atoms to form an octet.
How to write a formula.How to write a formula.
Write cation first, followed by anionExample:
Anion : P3-
Cation : Al3+
Formula : AlP
How to write a formula.How to write a formula.
• Compound must be neutral, so all charges must cancel
Write an ionic formula for Na+ bonding with F−
Balance the charges. Na+ F−
(1+) + (1-) = 0
1 Na+ and 1 F− = NaF
Write an ionic formula for Mg2+ bonding with Cl−
Balance the charges. Mg2+ Cl−
Cl−
(2+) + 2(1-) = 0
1 Mg2+ and 2 Cl− = Mg Cl2
Write an ionic formula for K+ bonding with S2−
Balance the charges. K+ S2−
K+
2(1+) + (2-) = 0
2 K+ and 1 S2− = K2S
Write the formula for…Write the formula for…
an ionic compound composed of:
Al3+ and S2-
Al2S3
Write an ionic formula for Fe3+ bonding with OH−
Balance the charges.Fe3+ OH−
OH− OH−
(3+) + 3(1-) = 0
1 Fe3+ and 3 OH− = Fe(OH)3
Let’s play the Ionic Bonding Let’s play the Ionic Bonding Dating Game!Dating Game!
Example: Aluminum ChlorideExample: Aluminum Chloride
Step 1:
Step 2:
Step 3: 1 3
Step 4: AlCl3
Criss-Cross Rule
Al Cl
Al Cl
3+ 1-
write out name with space
write symbols & charge of elements
criss-cross charges as subsrcipts
combine as formula unit(“1” is never shown)
Aluminum Chloride
Example: Aluminum OxideExample: Aluminum Oxide
Step 1: Aluminum Oxide
Step 2: Al3+ O2-
Step 3: Al O2 3
Step 4: Al2O3
Criss-Cross Rule
Example: Magnesium OxideExample: Magnesium Oxide
Step 1: Magnesium Oxide
Step 2: Mg2+ O2-
Step 3: Mg O2 2
Step 4: Mg2O2
Step 5: MgO
Criss-Cross Rule
InBr3BaS
Criss-Cross RuleCriss-Cross Rule
criss-cross rule: charge on cation / anion
“becomes” subscript of anion / cation
** Warning: Reduce to lowest terms.
Al2O3
Al3+ and O2–
Al2 O3
Ba2+ and S2–
Ba2 S2
In3+ and Br1–
In1 Br3
aluminum oxide barium sulfide indium bromide
Lesson Three--Transition Metal Lesson Three--Transition Metal CompoundsCompounds
Transition metals have electrons in d orbitals and can donate different numbers of electrons, thus giving them several different positive charges.
These can be determined from the Roman numeral which is written next to the metal's name.Example: Cu1+is Copper I
Pb2+is Lead IIFe3+is Iron IIISn4+s Tin IV
Metals with more than 1 chargeMetals with more than 1 charge
Examples:
• Cu + Copper (I)
• Cu+2 Copper (II)
• Fe+2 Iron (II)
• Fe+3 Iron (III)
PracticePractice
• K and Cl
• K and S
• Ca and S
• Cu (II) and S
Polyatomic Ions!!!!!!!!Polyatomic Ions!!!!!!!!
• A polyatomic ion is a charged species (ion) composed of two or more atoms covalently bonded.
• PO4-3 NH4
+1
Lewis Dot Structures for Polyatomic ions
H +
NH4+ H N H
H
• Al + PO4-3 K + SO4
-2
• Al +3 + PO4-3 K +1 + SO4
-2
• Al(PO4
) K2
(SO4
)
• Ca + PO4-3
• Ca +2 + PO4-3
• Ca3
(PO4
)2
Covalent bonding NotesCovalent bonding Notes
• Covalent bond: The sharing of a pair of electrons between 2
nonmetal atoms in order to fill its valence shell.
– Each atom gains 1 electron from each covalent bond it forms with another atom.
• When electron sharing usually occurs so that atoms attain a stable electron configuration and have 8 valence electrons.
Single Covalent Bonds Diatomic MoleculesSingle Covalent Bonds Diatomic Molecules
Each chlorine needs to gain one electron by sharing electrons each atom achieves stability .
Cl + Cl Cl Cl
The pair of shared electrons is often represented as a dash. Cl-Cl
Single Covalent Bonds Diatomic MoleculesSingle Covalent Bonds Diatomic Molecules
The chlorine atoms only share one pair of valence electrons. The electrons pairs not shared are called unshared electron pairs or lone pairs.
Cl + Cl Cl Cl
Single Covalent Bonds in compoundsSingle Covalent Bonds in compounds
• H20 is a molecule containing three atoms with two single covalent bonds.
• Count up the electrons you have!!!
• 2 H + O H O H
• The hydrogen and oxygen attain stable configurations by sharing electrons.
Your TurnYour Turn
• Example OF2
Double Covalent BondsDouble Covalent Bonds
Two pair of electrons are being shared.
S + S S S
Triple Covalent BondsTriple Covalent Bonds
Three pair of electrons are being shared.
P + P P P
Charged CompoundsCharged Compounds
• Some compounds do not satisfy their stable configuration and therefore have a charge on the compound.
• Example- NH4 +1
Exceptions to the Octet RuleThe octet rule cannot be satisfied in molecules whose total
number of valence electrons is an odd number. However, these molecules do exist in nature.
Examples:
Nitrogen dioxide (NO2)
Boron trifluoride (BF3)
Phosphorus pentachloride (PCl5) = 10 v.e- Expanded octet
Sulfur hexafluroride (SF6) = 12 v.e- Expanded octet
Nonpolar Covalent BondNonpolar Covalent Bond
• When atoms bond equally it is considered a nonpolar covalent bond.
• Cl2• O2
• N2
• H2
Polar Covalent BondPolar Covalent Bond
• When electrons are shared unequally it is a polar covalent bond.
• An atom that strongly attracts electrons is more electronegative and therefore gains a slightly negative charge.
• The less electronegative atom has a slightly positive charge.
• This results in a polar bond!
An arrow is used to show which element is donating the unshared pair of electrons.
The crossed end of the arrow indicates a pos. end and the arrow points in the direction of the neg. end
Example: H-Br
polar molecules are also called dipoles.
A dipole is a molecule with two partially charged ends or poles.
ExamplesExamples
• H-Br
• H2S
• SCl2
• CO2
C. JohannessonC. Johannesson
• Nonpolar Covalent Bond– e- are shared equally– symmetrical e- density– usually identical atoms
C. Bond PolarityC. Bond Polarity
C. JohannessonC. Johannesson
+ -
C. Bond PolarityC. Bond Polarity
• Polar Covalent Bond– e- are shared unequally– asymmetrical e- density– results in partial charges (dipole)
C. JohannessonC. Johannesson
+ -
+
B. Lewis StructuresB. Lewis Structures• Nonpolar Covalent - no charges
• Polar Covalent - partial charges
C. JohannessonC. Johannesson
A. Dipole MomentA. Dipole Moment
• Direction of the polar bond in a molecule.
• Arrow points toward the more e-neg atom.
H Cl+ -
C. JohannessonC. Johannesson
B. Determining Molecular PolarityB. Determining Molecular Polarity
• Nonpolar Molecules– Dipole moments are symmetrical and
cancel out.
BF3
F
F F
B
C. JohannessonC. Johannesson
B. Determining Molecular PolarityB. Determining Molecular Polarity
• Polar Molecules– Dipole moments are asymmetrical and don
’t cancel .
netdipolemoment
H2OH H
O
C. JohannessonC. Johannesson
CHCl3
H
Cl ClCl
B. Determining Molecular PolarityB. Determining Molecular Polarity
• Therefore, polar molecules have...– asymmetrical shape (lone pairs) or – asymmetrical atoms
netdipolemoment