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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)

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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

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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

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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?

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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

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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?

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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

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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-))

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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!

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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!

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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!

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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.

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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.

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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

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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

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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

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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

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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

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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).

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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

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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!!!

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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

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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.

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More Examples…More Examples…

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Shifting Gears: Polyatomic Ions…Shifting Gears: Polyatomic Ions…

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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)

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Some Compounds with Polyatomic IonsSome Compounds with Polyatomic Ions

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Some Compounds with Polyatomic IonsSome Compounds with Polyatomic Ions

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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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

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Flowchart for Naming Ionic CompoundsFlowchart for Naming Ionic Compounds

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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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

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KEY QUESTION: How do you determine which atom has the partial negative charge and which atom has

the partial positive charge?

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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.

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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

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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.

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• 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

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• 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

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Comparing Nonpolar & Polar Covalent BondsComparing Nonpolar & Polar Covalent Bonds

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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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