11
AnnouncementsAnnouncements & Agenda& Agenda (01/29/07)(01/29/07)
Pick up graded quizzes (Average = 8.2/10)Pick up graded quizzes (Average = 8.2/10) Note: Need more detailed/precise explanationsNote: Need more detailed/precise explanations
This week’s quiz moved to FridayThis week’s quiz moved to Friday
Today (4.3-4.6):Today (4.3-4.6): More on ionic & covalent compoundsMore on ionic & covalent compounds Naming and writing ionic & covalent compoundsNaming and writing ionic & covalent compounds Electronegativity & Bond Polarity (4.6)Electronegativity & Bond Polarity (4.6)
22
An amazing thing about the universe - Sometimes An amazing thing about the universe - Sometimes when things come together, they stick…when things come together, they stick…
• Protons and neutrons in a atomic nucleiProtons and neutrons in a atomic nuclei
• Atoms in moleculesAtoms in molecules
H H
H H
Last Time: Bonding OverviewLast Time: Bonding Overview
33
TWO EXTREME CASESTWO EXTREME CASES• Ionic bonding:Ionic bonding: results when “Atom A” results when “Atom A” transferstransfers an an
electron to “Atom B” (e.g. salts such as NaCl)electron to “Atom B” (e.g. salts such as NaCl)
• Covalent bonding:Covalent bonding: results when atoms results when atoms shareshare electronselectrons
• Polar-covalent bonding:Polar-covalent bonding: everything in between (a everything in between (a good portion of ‘reality’)good portion of ‘reality’)
Last Time: Chemical Bonds:Last Time: Chemical Bonds: attractive attractive force holding two or more atoms togetherforce holding two or more atoms together
44
Last Time: The Octet RuleLast Time: The Octet Rule
An octet in the outer shell An octet in the outer shell makes atoms stablemakes atoms stable
Electrons are lost, gained Electrons are lost, gained or shared to form an octetor shared to form an octet
Electronegativity (4.6): Electronegativity (4.6): How tightly does an atom How tightly does an atom tend to hold on to tend to hold on to electrons?electrons?
55
Atoms are electronically neutral Atoms are electronically neutral they do they do not have a charge.not have a charge. WHY? Charge from protons and electrons cancelWHY? Charge from protons and electrons cancel
But an atom can lose or gain electrons (it But an atom can lose or gain electrons (it cannot lose or gain protons…)cannot lose or gain protons…)
An An ionion – is a particle with an unequal number – is a particle with an unequal number of protons and electrons.of protons and electrons.
Last Time: IonsLast Time: Ions
66
IonsIons tend to form “octets.” tend to form “octets.” → Periodic Table→ Periodic Table
2 Flavors:2 Flavors:Cations Cations – positive charge, generally metal – positive charge, generally metal atoms – result from loss of 1 or more electrons.atoms – result from loss of 1 or more electrons.AnionsAnions – negative charge, generally nonmetals, – negative charge, generally nonmetals, result from gain of 1 or more electrons.result from gain of 1 or more electrons.
Carbon and boron do not form ionsCarbon and boron do not form ions
Why Do Ions Form?Why Do Ions Form?
77
Ionic Charges - CationsIonic Charges - CationsGroup 1AGroup 1A form cations with +1 charge. (Na form cations with +1 charge. (Na++, K, K++, Cs, Cs+ +
etc…)etc…)
Group 2AGroup 2A form cations with +2 charge. (Ba form cations with +2 charge. (Ba2+2+, Ca, Ca2+2+, , MgMg22+ etc…)+ etc…)
Metals in the middle (transition metals) can be variable Metals in the middle (transition metals) can be variable positive charge positive charge
88
Ionic Charges - AnionsIonic Charges - Anions
Group 7AGroup 7A elements tend to form anions with –1 charge. elements tend to form anions with –1 charge. (F(F--, Br, Br--, I, I-- etc..) etc..)
Group 6AGroup 6A elements tend to form anions with –2 charge. elements tend to form anions with –2 charge. (O(O2-2-, S, S2-2- etc…) etc…)
Groups 5AGroups 5A elements can (but rare) form –3 anions (N elements can (but rare) form –3 anions (N3-3-))
99
Ionic CompoundsIonic Compounds
A solid that contains cations and anions in A solid that contains cations and anions in a a balancedbalanced whole-number ratio is called an whole-number ratio is called an ionic compound.ionic compound. Electrons Electrons lostlost by the by the cationcation must equal the must equal the
electrons electrons gainedgained by the by the anionanion
Usually it is between a metal & a nonmetal.Usually it is between a metal & a nonmetal.
Example: NaClExample: NaCl
Important: When an ionic compound dissolves, it Important: When an ionic compound dissolves, it breaks apart into ions. Covalent compounds do not!breaks apart into ions. Covalent compounds do not!
1010
Formation of a Sodium Ion, NaFormation of a Sodium Ion, Na++
Sodium achieves an octet by losing its 1 valence electron.Sodium achieves an octet by losing its 1 valence electron.
2, 8, 12, 8, 1 2, 82, 8
By the way, cations are always smaller than By the way, cations are always smaller than their neutral counterparts!their neutral counterparts!
1111
Formation of a Chloride, ClFormation of a Chloride, Cl--
Chlorine achieves an octet by adding an electron to its Chlorine achieves an octet by adding an electron to its valence electrons.valence electrons.
2, 8, 72, 8, 7 2, 8, 82, 8, 8
By the way, anions are always bigger than their By the way, anions are always bigger than their neutral counterparts!neutral counterparts!
1212
Charge Balance for NaCl, “Salt”Charge Balance for NaCl, “Salt”
In NaCl,In NaCl,• a Na atom loses its valence electron. a Na atom loses its valence electron. • a Cl atom gains an electron.a Cl atom gains an electron.• the symbol of the metal is written the symbol of the metal is written firstfirst followed by the followed by the
symbol of the nonmetal.symbol of the nonmetal.
1313
Charge Balance In MgClCharge Balance In MgCl22
In MgClIn MgCl22,,
• a Mg atom loses 2 a Mg atom loses 2 valence electrons.valence electrons.
• two Cl atoms each two Cl atoms each
gain 1 electron.gain 1 electron.
• subscripts indicate subscripts indicate the number of ions the number of ions needed to give needed to give charge balance.charge balance.
1414
From Lab: Naming Ionic CompoundsFrom Lab: Naming Ionic Compounds
Name the metal first, then the nonmetal as Name the metal first, then the nonmetal as -ide-ide..Use name of a metal if it can only have one fixed Use name of a metal if it can only have one fixed
chargecharge
Groups 1A, 2A, 3AGroups 1A, 2A, 3A
and Ag (+1), Zn (+2), and Cd (+2)and Ag (+1), Zn (+2), and Cd (+2)
Examples:Examples:
NaClNaCl sodium chloridesodium chloride
ZnIZnI22 zinc iodidezinc iodide
AlAl22OO33 aluminum oxidealuminum oxide
1515
The formula of the ionic compound The formula of the ionic compound of Naof Na+ + and Oand O2-2- is is
0%
0%
0% 1.1. NaONaO
2.2. NaNa22OO
3.3. NaONaO22
11 22 33 44 55 66 77 88 99 1010 1111 1212 1313 1414 1515 1616 1717 1818 1919 2020
2121 2222 2323 2424 2525 2626 2727 2828 2929 3030 3131 3232 3333 3434 3535 3636 3737 3838 3939 4040
4141 4242 4343 4444 4545 4646 4747 4848 4949 5050
1616
The formula of a compound of The formula of a compound of calcium and sulfur is:calcium and sulfur is:
0%
0%
0% 1.1. CaCa22SS
2.2. CaSCaS22
3.3. CaSCaS
11 22 33 44 55 66 77 88 99 1010 1111 1212 1313 1414 1515 1616 1717 1818 1919 2020
2121 2222 2323 2424 2525 2626 2727 2828 2929 3030 3131 3232 3333 3434 3535 3636 3737 3838 3939 4040
4141 4242 4343 4444 4545 4646 4747 4848 4949 5050
1717
From Lab: From Lab: Transition MetalsTransition Metals
Most form 2 or more positive ions Most form 2 or more positive ions
1+1+ 2+ 1+ or 2+ 2+ or 3+ 2+ 1+ or 2+ 2+ or 3+
AgAg++ Cd Cd2+2+ Cu Cu++,, CuCu2+2+ Fe Fe2+2+, Fe, Fe3+3+
silver cadmium copper(I) ion silver cadmium copper(I) ion iron(II) ion iron(II) ion
ion ionion ion copper (II) ion iron(III) ioncopper (II) ion iron(III) ion
ZnZn2+2+
zinc ionzinc ion
1818
Names of Variable IonsNames of Variable Ions
Use a roman number after the name of a Use a roman number after the name of a metal that forms two or more ionsmetal that forms two or more ions
Transition metals and Transition metals and the metals in groups 4A and 5A the metals in groups 4A and 5A
FeClFeCl33 (Fe(Fe3+3+)) iron (III) chlorideiron (III) chloride
CuClCuCl (Cu(Cu++ ) ) copper (I) chloridecopper (I) chloride
SnFSnF44 (Sn(Sn4+4+)) tin (IV) fluoridetin (IV) fluoride
PbClPbCl22 (Pb(Pb2+2+))lead (II) chloridelead (II) chloride
FeFe22SS33 (Fe(Fe3+3+)) iron (III) sulfideiron (III) sulfide
1919
Flowchart for Naming Ionic CompoundsFlowchart for Naming Ionic Compounds
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
2020
Covalent BondsCovalent Bonds
Formed between atoms of groups (columns) 4A-Formed between atoms of groups (columns) 4A-7A (7A (nonmetalsnonmetals))
How do you form octets, if neither atom How do you form octets, if neither atom particularly wants to give up electrons?particularly wants to give up electrons?
Share Share Form single, double, and triple bonds to yield an Form single, double, and triple bonds to yield an
octetoctet
Applies to bonds between H, C, N, O, S, P, Applies to bonds between H, C, N, O, S, P, Halogens (F, Cl, etc) – not metals (usually).Halogens (F, Cl, etc) – not metals (usually).
2121
Each electron in bonding pair has greater space Each electron in bonding pair has greater space available than in the unbonded individual atoms, and available than in the unbonded individual atoms, and each gets to “feel” the positive charge of both nuclei.each gets to “feel” the positive charge of both nuclei.
Covalent Bonding: ConsiderationsCovalent Bonding: Considerations
2222
Diatomic MoleculesDiatomic Molecules
Gases that exist as diatomic moleculesGases that exist as diatomic molecules
are Hare H22, F, F22, N, N22, O, O22, Cl, Cl22, Br, Br22, I, I22
octetsoctets
N N + +
N N N N::::::NN triple bondtriple bondNOTE: For nitrogen to achieve its octet, it needs NOTE: For nitrogen to achieve its octet, it needs to form 3 bonds!!!to form 3 bonds!!!
2323
Lewis Structures: Covalent Bonds in NHLewis Structures: Covalent Bonds in NH33
Bonding pairsBonding pairs
HH
HH :: N N : : H H
Lone pair of electronsLone pair of electrons
DO LEWIS STRUCTURE ON BOARD
2424
Carbon forms 4 covalent bondsCarbon forms 4 covalent bonds
In a CHIn a CH44, methane, molecule, methane, molecule
• a C atom shares 4 electrons a C atom shares 4 electrons to attain an octet.to attain an octet.
• each H shares 1 electron to each H shares 1 electron to become stable like helium.become stable like helium.
2727
Polyatomic Ions: A Group of Covalently-Polyatomic Ions: A Group of Covalently-bonded Atoms with an Overall Charge.bonded Atoms with an Overall Charge.
KNOW THESE & Table 4.7:KNOW THESE & Table 4.7:
NHNH44++ ammoniumammonium OHOH-- hydroxide hydroxide
NONO33-- nitratenitrate NONO22
-- nitrite nitrite
COCO332-2- carbonatecarbonate
HCOHCO33-- hydrogen carbonate (bicarbonate)hydrogen carbonate (bicarbonate)
2828
Some Compounds with Polyatomic IonsSome Compounds with Polyatomic Ions
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
2929
Some Compounds with Polyatomic IonsSome Compounds with Polyatomic Ions
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
3030
Naming Ternary CompoundsNaming Ternary CompoundsContain at least 3 elementsContain at least 3 elementsName the nonmetals as a Name the nonmetals as a polyatomic ionpolyatomic ionExamples:Examples:
NaNaNONO33 Sodium Sodium nitratenitrate
KK22SOSO44 Potassium Potassium sulfatesulfate
AlAl(HCO(HCO33))33 AluminumAluminum bicarbonate bicarbonate
or or aluminumaluminum hydrogen hydrogen
carbonatecarbonate
3131
Flowchart for Naming Ionic CompoundsFlowchart for Naming Ionic Compounds
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
3232
Connecting the Extremes: In Between Connecting the Extremes: In Between Ionic and Covalent Bonds (4.6)Ionic and Covalent Bonds (4.6)
A A purepure covalent bond occurs only when covalent bond occurs only when two identical atoms are bonded: Ntwo identical atoms are bonded: N22
Polar Covalent BondPolar Covalent Bond: Unequal sharing : Unequal sharing between two dissimilar atoms between two dissimilar atoms Therefore, the electrons are nearer to one of Therefore, the electrons are nearer to one of
the atoms, and that atom acquires a the atoms, and that atom acquires a partial partial negative charge (negative charge ()). .
And consequently the other atom has a And consequently the other atom has a partial partial positive charge positive charge
3333
KEY QUESTION: How do you determine which atom has the partial negative charge and which atom has
the partial positive charge?
3434
Electronegativity: Ability of an Electronegativity: Ability of an Element to Draw Electrons to ItselfElement to Draw Electrons to Itself The attraction of an atom for electrons is called its The attraction of an atom for electrons is called its
electronegativity.electronegativity.Can be represented with numerical valuesCan be represented with numerical valuesLarger numbers mean a greater attraction for electronsLarger numbers mean a greater attraction for electrons
Fluorine has the greatest electronegativity.Fluorine has the greatest electronegativity.
THE TREND TO KNOW:THE TREND TO KNOW:
Elements in the upper-right corner have the greatest EN Elements in the upper-right corner have the greatest EN values.values.
Elements in the lower-left corner have the smallest EN Elements in the lower-left corner have the smallest EN values.values.
3535
Some Electronegativity Values for Some Electronegativity Values for Group A ElementsGroup A Elements
Copyright © 2005 by Pearson Education, Inc.Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin CummingsPublishing as Benjamin Cummings
Low Low valuesvalues
High High valuesvalues
`̀ Electronegativity increasesElectronegativity increases
`̀ E
lectrone
gativity d
ecrease
sE
lectrone
gativity d
ecrease
s
3636
The Two Extremes Revisited…The Two Extremes Revisited…
The greater the difference of the EN values, the more polar the bond! An EN difference ≥ 1.8 is considered an ionic bond.
3737
• occur between nonmetals.occur between nonmetals.• have equal or almost equal sharing of electrons.have equal or almost equal sharing of electrons.• have almost no electronegativity difference (0.0 to 0.4).have almost no electronegativity difference (0.0 to 0.4).
ExamplesExamples: : ElectronegativityElectronegativity Atoms Atoms DifferenceDifference Type of Bond Type of Bond
N-NN-N 3.0 - 3.0 = 3.0 - 3.0 = 0.00.0 Nonpolar covalent Nonpolar covalent
Cl-BrCl-Br 3.0 - 2.8 = 3.0 - 2.8 = 0.20.2 Nonpolar covalent Nonpolar covalentH-SiH-Si 2.1 - 1.8 = 2.1 - 1.8 = 0.30.3 Nonpolar covalent Nonpolar covalent
Nonpolar Covalent BondsNonpolar Covalent Bonds
3838
• occur between nonmetal atoms.occur between nonmetal atoms.• have an unequal sharing of electrons.have an unequal sharing of electrons.• have a moderate electronegativity difference (0.5 to 1.7).have a moderate electronegativity difference (0.5 to 1.7).
ExamplesExamples: : ElectronegativityElectronegativity
Atoms Atoms DifferenceDifference Type of BondType of BondO-ClO-Cl 3.5 - 3.0 = 3.5 - 3.0 = 0.50.5 Polar covalentPolar covalentCl-CCl-C 3.0 - 2.5 = 3.0 - 2.5 = 0.50.5 Polar covalentPolar covalentO-S O-S 3.5 - 2.5 = 3.5 - 2.5 = 1.01.0 Polar covalentPolar covalent
Polar Covalent BondsPolar Covalent Bonds
3939
Comparing Nonpolar & Polar Covalent BondsComparing Nonpolar & Polar Covalent Bonds
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
4040
Ionic BondsIonic Bonds
• occur between metal and nonmetal ions.occur between metal and nonmetal ions.• form as a result of electron transfer.form as a result of electron transfer.• have a large electronegativity difference (1.8 or more).have a large electronegativity difference (1.8 or more).
ExamplesExamples: : ElectronegativityElectronegativity
Atoms Atoms DifferenceDifference Type of Bond Type of Bond
Cl-KCl-K 3.0 – 0.8 3.0 – 0.8 = = 2.22.2 IonicIonic
N-NaN-Na 3.0 – 0.9 3.0 – 0.9 = = 2.12.1 Ionic Ionic
S-CsS-Cs 2.5 – 0.72.5 – 0.7 = = 1.81.8 Ionic Ionic
Top Related