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AnnouncementsAnnouncements & Agenda& Agenda (01/26/07)(01/26/07)

You should finish reading Ch 4 and start Ch 5 over You should finish reading Ch 4 and start Ch 5 over the weekend.the weekend.Quiz today!Quiz today!

Today (4.1-4.3, 4.5):Today (4.1-4.3, 4.5): Ionic vs. covalent bonding & the Octet RuleIonic vs. covalent bonding & the Octet Rule Ionic and covalent compoundsIonic and covalent compounds Naming and writing ionic compoundsNaming and writing ionic compounds

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Last time: Electrons in Energy LevelsLast time: Electrons in Energy Levels

Energy Orbitals Maximum Energy Orbitals Maximum Total Total Level (Shell) No. of ElectronsLevel (Shell) No. of Electrons ElectronsElectrons11 1 1ss 2 2 2222 2 2ss 2 2 88

22pp 6 633 3 3ss 2 2 1818

33pp 6 6 33dd 1010

44 4 4ss 2 2 3232 44pp 6 6 44dd 1010

44ff 1414How do we know orbitals exist??? SpectroscopyHow do we know orbitals exist??? Spectroscopy

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Last Time: Periodic LawLast Time: Periodic Law

All the elements in a group have the same electron All the elements in a group have the same electron configuration in their outermost shellsconfiguration in their outermost shells

Outermost electrons are called Outermost electrons are called valence electronsvalence electrons

Elements with same # of valence electrons display Elements with same # of valence electrons display similar chemical & physical properties!!!similar chemical & physical properties!!!

Example: Example: Group 2Group 2

BeBe 2, 2, 22

Mg 2, 8, Mg 2, 8, 22

Ca Ca 2, 2, 8, 2, 2, 8, 22

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Last time: Metals, Nonmetals, & MetalloidsLast time: Metals, Nonmetals, & Metalloids

The heavy zigzag line The heavy zigzag line separates metals and separates metals and nonmetals.nonmetals.• MetalsMetals are located to are located to

the left.the left.• NonmetalsNonmetals are located are located

to the right. to the right. • MetalloidsMetalloids are located are located

along the heavy along the heavy zigzag line between zigzag line between the metals and the metals and nonmetals.nonmetals.

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

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Last Time: More Periodic TrendsLast Time: More Periodic Trends

How Atomic Orbital filling affects:How Atomic Orbital filling affects: Atomic Size (Radius)Atomic Size (Radius) Ionization Energy Ionization Energy

Definitions….Definitions….

Ionization Energy : Cost of removing an eIonization Energy : Cost of removing an e-- from a neutral atomfrom a neutral atom

Atomic Radii: Distance between center of Atomic Radii: Distance between center of nucleus and outer electron shellnucleus and outer electron shell

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30 Good Practice Problems (Ch 4)30 Good Practice Problems (Ch 4)

11 22 33 44 55

4.01, 4.05, 4.07, 4.09, 4.11, 4.13, 4.01, 4.05, 4.07, 4.09, 4.11, 4.13, 4.15, 4.17, 4.23, 4.25, 4.35, 4.37, 4.15, 4.17, 4.23, 4.25, 4.35, 4.37, 4.41, 4.45, 4.47, 4.49, 4.53, 4.55, 4.41, 4.45, 4.47, 4.49, 4.53, 4.55, 4.57, 4.59, 4.63, 4.65, 4.67, 4.69, 4.57, 4.59, 4.63, 4.65, 4.67, 4.69, 4.85, 4.87, 4.93, 4.97, 4.103, and 4.85, 4.87, 4.93, 4.97, 4.103, and 4.1054.105

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Chemical BondsChemical Bonds

Attraction between two or more atomsAttraction between two or more atomsInteraction between valence electronsInteraction between valence electronsIonic bondsIonic bondsCovalent bondsCovalent bonds

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An amazing thing about the universe - It works in a way that sometimes when things come together, they stick…

• Protons and neutrons in a atomic nuclei

• Atoms in molecules

H H

H H

Bonding OverviewBonding 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’)

Chemical Bonds:Chemical Bonds: attractive force holding attractive force holding two or more atoms togethertwo or more atoms together

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Guiding Principle: The Octet RuleGuiding Principle: The Octet Rule

An octet in the outer shell An octet in the outer shell makes atoms stablemakes atoms stable

Electrons are Electrons are lost, gained, lost, gained, or sharedor shared to form an octetto 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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Reminder: Valence ElectronsReminder: Valence Electrons

Electrons in the Electrons in the highest (outer)highest (outer) electron level electron level

Have most contact with other atoms Have most contact with other atoms

Known as Known as valencevalence electrons electrons

Outer shells of noble gases contain Outer shells of noble gases contain 8 valence 8 valence

electronselectrons (except He = 2)(except He = 2)

ExampleExample: : Ne Ne 2, 2, 88

ArAr 2, 8, 2, 8, 88

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Electron Dot StructuresElectron Dot Structures

Symbols of atoms with dots to represent the valence-Symbols of atoms with dots to represent the valence-shell electrons shell electrons

1A 2A 3A 4A 5A 6A 7A 8A1A 2A 3A 4A 5A 6A 7A 8A

HH He: He:

LiLi BeBe B B C C N N O O :: F F ::Ne Ne ::

NaNa Mg Mg Al Al SiSi PP SS ::Cl Cl ::Ar Ar ::

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XX:: would be the electron dot would be the electron dot formula for:formula for:

0%

0%

0%

1.1. NaNa

2.2. MgMg

3.3. AlAl

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would be the electron dot would be the electron dot formula for:formula for:

0%

0%

0%

1.1. BB

2.2. CC

3.3. NN

XX

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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.

Charged Atoms: IonsCharged Atoms: 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

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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, 1 2, 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, 7 2, 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

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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

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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

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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: In covalent compounds, nitrogen needs to form 3 bonds to obtain its octet!!!

3333

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.