LECTURE 6.2LECTURE 6.2

LECTURE OUTLINELECTURE OUTLINE

Weekly ReadingWeekly ReadingPrototype Practice Quiz 6: FeedbackPrototype Practice Quiz 6: FeedbackThe Periodic TableThe Periodic Table

CHAPTER XVII: THE CHAPTER XVII: THE METALLIC BONDMETALLIC BOND

Chapter 17 introduces the reader to the metallic bond: Chapter 17 introduces the reader to the metallic bond: an oft-ignored "strong" bond, but one that is an oft-ignored "strong" bond, but one that is responsible for bonding in all metallic materials, responsible for bonding in all metallic materials, virtually 75% of all known elements. It is shown that virtually 75% of all known elements. It is shown that the "simple" nature of the metallic bond results in the "simple" nature of the metallic bond results in "close-packed" crystalline structures. The reader is "close-packed" crystalline structures. The reader is introduced to the three major metallic structures: introduced to the three major metallic structures: cubic close packed, hexagonal close packed, and cubic close packed, hexagonal close packed, and body centered cubic. Chapter 17 also "hints" at the body centered cubic. Chapter 17 also "hints" at the properties of metallic materials, in particular their properties of metallic materials, in particular their melting points and their ductility.melting points and their ductility.

CHAPTER XVIII: THE VAN CHAPTER XVIII: THE VAN DER WAALS BOND DER WAALS BOND

Chapter 18 opens with a question: How can molecular materials, such Chapter 18 opens with a question: How can molecular materials, such as O2, H2 and CO2 form liquids, much less solids?as O2, H2 and CO2 form liquids, much less solids?

If a material is composed of "molecules," then the atoms that If a material is composed of "molecules," then the atoms that constitute the molecule have attained the "magical octet" of outer-constitute the molecule have attained the "magical octet" of outer-shell electrons. So, what driving force could there be for molecules to shell electrons. So, what driving force could there be for molecules to bond to each other? In Chapter 18, one of two possible answers is bond to each other? In Chapter 18, one of two possible answers is given—it is called the van der Waals bond. This bond is weak and is given—it is called the van der Waals bond. This bond is weak and is associated with "fluctuating dipoles" on individual atoms.associated with "fluctuating dipoles" on individual atoms.

Chapter 18 presents several examples of materials within which the Chapter 18 presents several examples of materials within which the van der Waals bond is of some importance. It also differentiates van der Waals bond is of some importance. It also differentiates between intramolecular bonds and intermolecular bonds. These terms between intramolecular bonds and intermolecular bonds. These terms are only meaningful in molecular materials (i.e., those in which the are only meaningful in molecular materials (i.e., those in which the strong bond is covalent).strong bond is covalent).

CHAPTER XIX: THE CHAPTER XIX: THE HYDROGEN BOND HYDROGEN BOND

The two secondary or weak bonds are van der Waals (Chapter The two secondary or weak bonds are van der Waals (Chapter 18) and "hydrogen" (this chapter). Because the hydrogen bond 18) and "hydrogen" (this chapter). Because the hydrogen bond is responsible for the unique properties of water, Chapter 19 is responsible for the unique properties of water, Chapter 19 concentrates on the hydrogen bonding in the only common concentrates on the hydrogen bonding in the only common liquid on planet Earth: water.liquid on planet Earth: water.

The hydrogen bond is shown to result from a permanent dipole The hydrogen bond is shown to result from a permanent dipole that is created on a molecule, which consists of an that is created on a molecule, which consists of an electropositive and an electronegative atom. Following a electropositive and an electronegative atom. Following a description of the hydrogen bond, the unusual properties of description of the hydrogen bond, the unusual properties of water are explained in terms of the relative strengths of the water are explained in terms of the relative strengths of the van der Waals bond and the hydrogen bond. Finally, the van der Waals bond and the hydrogen bond. Finally, the mechanism for the formation of snowballs is demystified!mechanism for the formation of snowballs is demystified!

CHAPTER XX: THE CHAPTER XX: THE STRUCTURE OF POLYMERS STRUCTURE OF POLYMERS

The structure of polymers is described with specific reference The structure of polymers is described with specific reference to the covalent bond, which is "primary" and strong, and to the to the covalent bond, which is "primary" and strong, and to the secondary and weak bonds, van der Waals and hydrogen.secondary and weak bonds, van der Waals and hydrogen.

A distinction is drawn between thermoplastic polymers and A distinction is drawn between thermoplastic polymers and thermosetting polymers. The thermoplastic polymers are thermosetting polymers. The thermoplastic polymers are described in terms of the primary and secondary bonds, and described in terms of the primary and secondary bonds, and the differences between linear and branched polymers are the differences between linear and branched polymers are presented. The chapter explains thermosetting polymers in presented. The chapter explains thermosetting polymers in terms of the creation of strong, intermolecular bonds that are terms of the creation of strong, intermolecular bonds that are typically covalent. The crystalline nature and microstructure of typically covalent. The crystalline nature and microstructure of polymers is described briefly, and a discussion on the various polymers is described briefly, and a discussion on the various states of matter, as applied to polymeric materials, is states of matter, as applied to polymeric materials, is presented.presented.

PRACTICE QUIZ #6: PRACTICE QUIZ #6: FEEDBACKFEEDBACK

Q5. The three primary bonds are:Ionic, which form between a metal and a non-metal (e.g.,

NaCl).Covalent, which form between a non-metal and a non-metal

(e.g., CO2).Metallic, which form between atoms of metallic elements

(e.g., in bronzes).Use the above information to answer the following question.

Oxygen (O2) is a molecular material.<a+> True<b> False<F> True. Oxygen is a non-metal and two oxygen atoms bond covalently to each other forming an O2 molecule. Note that in the O2 molecule, each bond consists of two bonding pairs (i.e., it is a “double bond”).

Q6. Phosphorus has an effective nuclear charge of 15.<a> True<b+> False <F> False. The effective nuclear charge of an element is numerically the same as the number of outer-shell electrons, which for phosphorus is 5. Note that the effective nuclear charge is a measure of the force of attraction between the nucleus (positive) and the outer-shell electrons (negative). The “effective” nucleus is taken to be comprised of the “real” nucleus plus all of the inner electron shells. The effective charge on this effective nucleus is given by the number of protons in the real nucleus minus the number of electrons in the inner shells. Each electron in the outer shell is then attracted to the nucleus by the effective nuclear charge.

Q7. Which of the following phenomena contribute to the stability of the noble gases?<a> They have closed s and/or p shells, containing 2 and 8 electrons, respectively.<b> For a given period, they are characterized by the highest value of the "effective nuclear charge."<c> They have the highest ionization energies in a particular period.<d> They have closed s and/or p shells, containing 2 and 8 electrons, respectively, and for a given period, they are characterized by the highest value of the "effective nuclear charge."<e+> They have closed s and/or p shells, containing 2 and 8 electrons, respectively, and for a given period, they are characterized by the highest value of the "effective nuclear charge," and they have the highest ionization energies in a particular period.

<F> The noble gases have closed or filled outer shells (2 for the K-shell and 8 for the remainder). A closed outer shell implies a symmetric electron distribution, with little or no tendency to form dipoles. The effective nuclear charge is equal to 8 (other than for helium, which is 2). This is the highest value for any element within a given period and so the outer-shell electrons are most strongly bonded to the nucleus. Consequently, the ionization energy, which is the energy needed to remove an outer-shell electron, is highest, in a given period, for the noble gas.

Q8. Titanium is_____.<a> in Period 4<b> a transition metal<c> lustrous<d> in Period 4 and a transition metal<e+> in Period 4, a transition metal, and lustrous<F> Titanium can be located using its atomic number. It is found in Period 4, between Groups II and III (i.e., it is a transition metal). Because it is a metal, it is lustrous.

Q9. The Wayward islanders are just beginning to develop their own version of the periodic table, but many elements are yet to be discovered. The islanders use their own convention to discriminate between periods and groups. For example, in Period Q, several elements are known to exist. Their atomic weights are 40, 44, 46, 48, 50, 52 and 54. Recently, another element has been isolated, and it is known that it belongs to Period Q, but the islanders have lost the information about its atomic weight. Which of the following values do you think is most likely?<a> 49<b> 51<c> 45<d> 53<e+> 42<F> Reference to the listed atomic weights shows that there is a difference of 2 between adjacent elements. However, the "gap" between 40 and 44 is 4, which suggests a missing element. An atomic weight of 42 rather neatly fills this gap!

LESSON 6: THE LESSON 6: THE PERIODIC TABLEPERIODIC TABLE

Electronic Structure of the ElementsElectronic Structure of the ElementsThe Periodic TableThe Periodic TableAtomic RadiiAtomic RadiiIonization EnergiesIonization EnergiesMetals and Non-MetalsMetals and Non-Metals

INNER AND OUTER SHELLSINNER AND OUTER SHELLS

The maximum number of electrons that The maximum number of electrons that may be associated with an inner shell is may be associated with an inner shell is either equal to or greater than the either equal to or greater than the maximum number of electrons, when that maximum number of electrons, when that shell is an outer shell.shell is an outer shell.

ENERGY LEVELS FOR A ENERGY LEVELS FOR A “MANY ELECTRON” ATOM“MANY ELECTRON” ATOM

The K-shell contains 2 electrons The K-shell contains 2 electrons only: the 1s electrons.only: the 1s electrons.

The L-shell may contain a The L-shell may contain a maximum of 8 electrons: 2s and maximum of 8 electrons: 2s and 2p.2p.

The M-shell may contain up to The M-shell may contain up to 18 electrons: 3s, 3p, and 3d18 electrons: 3s, 3p, and 3d

However, after the 3s and 3p However, after the 3s and 3p levels are filled, the next levels are filled, the next electron occupies a 4s level.electron occupies a 4s level.

The first series of “transition The first series of “transition elements” are those elements elements” are those elements whose inner 3d shell is being whose inner 3d shell is being filled.filled.

ELECTRONIC STRUCTURESELECTRONIC STRUCTURES The K-shell contains 2 electrons The K-shell contains 2 electrons

only: the 1s electrons.only: the 1s electrons. The L-shell may contain a The L-shell may contain a

maximum of 8 electrons: 2s and maximum of 8 electrons: 2s and 2p.2p.

The M-shell may contain up to The M-shell may contain up to 18 electrons: 3s, 3p, and 3d.18 electrons: 3s, 3p, and 3d.

However, after the 3s and 3p However, after the 3s and 3p levels are filled, the next levels are filled, the next electron occupies a 4s level.electron occupies a 4s level.

The first series of “transition The first series of “transition elements” are those elements elements” are those elements whose inner 3d shell is being whose inner 3d shell is being filled.filled.

THE GROUP IV ELEMENTSTHE GROUP IV ELEMENTS

Carbon: Period 2

Silicon: Period 3

Germanium: Period 4

ABBREVIATED PERIODIC ABBREVIATED PERIODIC TABLETABLE

THE MAGICAL OCTET!THE MAGICAL OCTET!For all outer shells, other than the K-shell, an For all outer shells, other than the K-shell, an

atom will try to attain a full outer shell, atom will try to attain a full outer shell, consisting of eight electrons (the K-shell is consisting of eight electrons (the K-shell is complete with only two).complete with only two).

An atom will seek this magical octet by An atom will seek this magical octet by donating, accepting, or sharing outer-shell donating, accepting, or sharing outer-shell electrons with other atoms.electrons with other atoms.

It is this donating, accepting, or sharing of It is this donating, accepting, or sharing of electrons that gives rise to “bonding”!electrons that gives rise to “bonding”!

METALS AND NON-METALSMETALS AND NON-METALS Metals will be defined as electron donors and non-Metals will be defined as electron donors and non-

metals will be defined as electron acceptors.metals will be defined as electron acceptors. In a very crude first approximation, we shall assume In a very crude first approximation, we shall assume

that it is relatively easy to lose a small number of that it is relatively easy to lose a small number of outer-shell electrons and also relatively easy to gain a outer-shell electrons and also relatively easy to gain a small number.small number.

Hence, “define” (?) a metal as an element that contains Hence, “define” (?) a metal as an element that contains three outer-shell electrons or fewer.three outer-shell electrons or fewer.

Then a non-metal will contain five or more outer-shell Then a non-metal will contain five or more outer-shell electrons (?).electrons (?).

This leaves us with the Group IV elements!This leaves us with the Group IV elements!

METALS AND NON-METALS: A METALS AND NON-METALS: A FIRST ATTEMPT!FIRST ATTEMPT!

EFFECTIVE NUCLEAR EFFECTIVE NUCLEAR CHARGECHARGE

The “effective nuclear charge” is a measure of how The “effective nuclear charge” is a measure of how strongly the outer-shell electrons are attracted to the strongly the outer-shell electrons are attracted to the nucleus.nucleus.

As the effective nuclear charge increases, the outer-As the effective nuclear charge increases, the outer-shell electrons get closer to the nucleus, and the radius shell electrons get closer to the nucleus, and the radius of the atom decreases.of the atom decreases.

As the outer-shell electrons get closer to the nucleus, As the outer-shell electrons get closer to the nucleus, they become more difficult to “remove” from the they become more difficult to “remove” from the atom, and the “ionization energy” increases.atom, and the “ionization energy” increases.

METALS TEND TO HAVE LOW IONIZATION METALS TEND TO HAVE LOW IONIZATION ENERGIES!ENERGIES!

EFFECTIVE NUCLEAR EFFECTIVE NUCLEAR CHARGE: PERIOD 3CHARGE: PERIOD 3

aa

Each outer electron "sees" aneffective nuclear charge(effective attractive force) of +1Each outer electron "sees" aneffective nuclear charge(effective attractive force) of +2Outer Shell ElectronsSodiumNa 2....8....1MagnesiumMg 2....8....2NucleusInner Shell Electrons12+10-11+10-

EFFECTIVE NUCLEAR EFFECTIVE NUCLEAR CHARGES, ATOMIC RADII, CHARGES, ATOMIC RADII,

IONIZATION ENERGIES, ETC.IONIZATION ENERGIES, ETC. The effective nuclear charge in Period 3 increases going from The effective nuclear charge in Period 3 increases going from

left to right.left to right. We would therefore predict that in going across Period 3, for We would therefore predict that in going across Period 3, for

example, the atomic radii will decrease.example, the atomic radii will decrease. Hence, the ionization energies increase going from left to right!Hence, the ionization energies increase going from left to right! In going “north to south” in a given group, the effective nuclear In going “north to south” in a given group, the effective nuclear

charge remains the same, but the outer shell becomes more charge remains the same, but the outer shell becomes more remote from the nucleus as the number of inner shells increases.remote from the nucleus as the number of inner shells increases.

Hence, ionization energies decrease going north to south in a Hence, ionization energies decrease going north to south in a given group!given group!

ATOMIC RADII: A PERIODIC ATOMIC RADII: A PERIODIC FUNCTIONFUNCTION

a) The Group I Elements b) The Period 3 Elementsa) The Group I Elements b) The Period 3 Elements

THE ATOMIC RADII OF THE THE ATOMIC RADII OF THE PERIOD 4 ELEMENTSPERIOD 4 ELEMENTS

EFFECTIVE NUCLEAR EFFECTIVE NUCLEAR CHARGES, ATOMIC RADII, CHARGES, ATOMIC RADII,

IONIZATION ENERGIES, ETC.IONIZATION ENERGIES, ETC. The effective nuclear charge in Period 3 increases going from The effective nuclear charge in Period 3 increases going from

left to right.left to right. Therefore, we would predict that in going across Period 3, for Therefore, we would predict that in going across Period 3, for

example, the atomic radii will decrease.example, the atomic radii will decrease. Hence, the ionization energies increase going from left to right!Hence, the ionization energies increase going from left to right! In going “north to south” in a given group, the effective nuclear In going “north to south” in a given group, the effective nuclear

charge remains the same, but the outer shell becomes more charge remains the same, but the outer shell becomes more remote from the nucleus as the number of inner shells increases.remote from the nucleus as the number of inner shells increases.

Hence, ionization energies decrease going north to south in a Hence, ionization energies decrease going north to south in a given group!given group!

IONIZATION ENERGIES: IONIZATION ENERGIES: METALS AND NON-METALSMETALS AND NON-METALS

THE GROUP IV ELEMENTSTHE GROUP IV ELEMENTS

Carbon: Period 2

Silicon: Period 3

Germanium: Period 4

EFFECTIVE NUCLEAR EFFECTIVE NUCLEAR CHARGES, ATOMIC RADII, CHARGES, ATOMIC RADII,

IONIZATION ENERGIES, ETC.IONIZATION ENERGIES, ETC. The effective nuclear charge in Period 3 increases going from The effective nuclear charge in Period 3 increases going from

left to right.left to right. Therefore, we would predict that, in going across Period 3, for Therefore, we would predict that, in going across Period 3, for

example. the atomic radii will decreaseexample. the atomic radii will decrease Hence, the ionization energies increase going from left to right!Hence, the ionization energies increase going from left to right! In going “north to south” in a given group, the effective nuclear In going “north to south” in a given group, the effective nuclear

charge remains the same, but the outer shell becomes more charge remains the same, but the outer shell becomes more remote from the nucleus as the number of inner shells increases.remote from the nucleus as the number of inner shells increases.

Hence, ionization energies decrease going north to south in a Hence, ionization energies decrease going north to south in a given group!given group!

THE GROUP IV ELEMENTS: THE GROUP IV ELEMENTS: IONIZATION ENERGIESIONIZATION ENERGIES

THE GROUP IV ELEMENTSTHE GROUP IV ELEMENTSFor carbon, the outer shell is the L-shell. For carbon, the outer shell is the L-shell.

Hence, the four outer-shell electrons are Hence, the four outer-shell electrons are strongly bound to the nucleus and the strongly bound to the nucleus and the ionization energy is very high. Carbon in the ionization energy is very high. Carbon in the guise of diamond is a prototypical non-metal.guise of diamond is a prototypical non-metal.

For lead, the outer shell is the P-shell. The For lead, the outer shell is the P-shell. The outer-shell electrons are only weakly bound outer-shell electrons are only weakly bound and lead is a typical metal.and lead is a typical metal.

IN THE MIDDLE ARE THE IN THE MIDDLE ARE THE SEMICONDUCTORS: SILICON AND SEMICONDUCTORS: SILICON AND GERMANIUM.GERMANIUM.

ATOMIC RADII AND ATOMIC RADII AND IONIZATION ENERGIES: IONIZATION ENERGIES: PERIODIC PROPERTIESPERIODIC PROPERTIES

IONIZATION ENERGIES: IONIZATION ENERGIES: METALS AND NON-METALSMETALS AND NON-METALS

METALS AND NON-METALSMETALS AND NON-METALS