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Announcements

• Exam 2 is this Thursday, Nov 1• Practice Exam 2 and its corresponding Answer Key are posted

• You will have 65 min, rather than 60 min, for Exam 2.• The Cover Sheet on Exam 2 will be slightly different from that on Practice

Exam 2; it will be like the Cover Sheet that was on Exam 1.• The Table of Electronegativities that was on Practice Exam 2 will not be on

Exam 2.

• There was a change in the schedule for the lead experiment– we will meet today during office hours (after class, 7th floor lounge).

• There is no class next Tuesday, Nov 6 (Election Day). L. We will therefore meet again next Thursday, Nov 8.

Today and Next Thursday• Today:

• Review and Finish Ch 12• Review: Valence vs Core Electrons• Periodic Trends in Atomic Properties

• Ionization Energies• Electron Affinities• Electronegativity• Atomic and Ionic Radii

• Isoelectronic Atoms and Ions• Zeff

• Review: “Aufbau”, Building Up Atoms

• Begin Ch 13• Bonding• Covalent vs Ionic Bonding• Lewis Dot Structures

• Next Thursday, Nov 8:• Ch 13

How many valence electrons does a neutral P atom have? Note Z=15.

• A) 0• B) 3• C) 4• D) 5• E) 6

Question 66

How many valence electrons does a neutral Mn atom have? Note Z=25.

• A) 4• B) 5• C) 6• D) 7• E) 8

Question 67

How many valence electrons does a neutral I atom have? Note Z=53.

• A) 4• B) 5• C) 6

• D) 7• E) 17

Question 68

Noble Configurations2 1s10 2s,2p18 3s,3p36 [4s,3d],4p54 [5s,4d],5p86 [6s,4f,5d,]6p

How many valence electrons does a P⎼ anion have? Note Z=15.

• A) 0• B) 3• C) 4

• D) 5• E) 6

Question 69


Valence: The number and configurations of electrons in the outermost shell determine important properties• Number of valence electrons is needed to draw Lewis structures.• Similar electronic configurations within each group give rise to similar

chemical properties. There are referred to as periodic properties.

Oxides: The Stoichiometry of Metal : Oxygen is a hallmark of the Group Transition Metals Mirror the Main Group

Li2O BeO B2O3 CO2 NO3- [O] F- Ne

Na2O MgO Al2O3/Sc2O3

SiO2/TiO2

PO43-/

VO43-

SO42-

CrO42-

Cl-ClO4

-

MnO4-

Ar

K2O/Cu2O

CaO/ZnO

Ga2O3/Y2O3

GeO2 /ZrO2

AsO43-

NbO43-

SeO42-

MoO42-

Br -

BrO4-

TcO4-

Kr

Rb2O/Ag2O

SrO/CdO

In2O3/Lu2O3

SnO2 /HfO2

SbO43- TeO4

2-

WO42-

I-

IO4-

Xe

IA/IB

IIA/IIB

IIIA/IIIB

IVA/IVB

VA/VB

VIA/VIB

VIIA/VIIB

VIIIA/VIIIB

2

Periodic Trends in Atomic Properties

I. Alkali metals: (H), Li, Na, K, Rb, CsII. Alkaline earth metals: Be, Al, Ca, Sr, Ba, RaIII. Boron family: B, Al, Ga, In, TlIV. Carbon family: C, Si, Ge, Sn, PbV. Nitrogen group (Pnictogens): N, P, As, Sb, BiVI. Chalcogens: O, S, Se, Te, PoVII. Halogens: F, Cl, Br, I, AtVIII. Noble gases: He, Ne, Ar, Kr, Xe, Rn

Eight Groups of Main Group Elements


81982_12_39.jpg

Metals:Good electrical and heat conductorsDuctile - can be stretched into wire.Possess metallic shine and luster.Typically 1-3 electrons in their outer shell.Lose their valence electrons easily


• Similar valence configurations give rise to similar reactivity andtypes of compounds that are formed stably, for example • Members of the same group have the same stoichiometry in the

oxides• Metals vs Nonmetals• Related to periodic trends in Ionization Energy, Electron Affinity,

Electronegativity• For example, F and Cl with 7 valence electrons easily gain one

electron to attain filled valence shells, while Na and K with one valence electron easily lose one electron to attain filled valence shells • Periodic trends in size (radius)


First Ionization EnergyM(g) à M+ (g) + e-

Energy change is positive (the electron was stably bound and is less stable when liberated)

Periodic Trends in Atomic Properties: Ionization Energy

• Large range in values follows periodic trends. K gives up an electron to form K+ much more readily than Cl or Ar.

• White: electron is easily removed (Group 1, Alkali)

• Red: hardest to remove (Group 8)

• Increases left to right, decreases top to bottom

First Ionization EnergyPeriodic Trends in Atomic Properties: Ionization Energy

Ionization energies increase across a period due to an increase in nuclear charge which causes the electron to be held more tightly.


• M+ (g) à M2+ (g) + e-

• Energy change is positive and even larger than the first (the electron is stably bound in the cation, more so than in the neutral atom)

• Also follow periodic trends.

Second Ionization EnergyPeriodic Trends in Atomic Properties: Ionization Energy

Core and Valence ElectronsThe successive ionization energies support the idea of a core and valence set of electrons. Consider the 11 ionization energies of sodium.

--One electron is easily removed,-- Then there is a group of eight electrons that are more tightly bound with monotonically increasing ionization energies, and --Finally there is a large jump for ionization of the last two electrons.

Sodium’s electrons can be thought of as being organized into three shells of electrons containing2, 8, and 1 electrons respectively. The last one (weakest bound) is the valence shell.

(kJ/mol)IE1 496IE2 4,562IE3 6,910IE4 9,543IE5 13,353IE6 16,610IE7 20,114IE8 25,496IE9 28,932IE10 141,362IE11. 159,076


Na Z=11 1s2 2s2 2p6 3sMg Z=12 1s2 2s2 2p6 3s2

Ionization energies support the idea of “shells” of tightly bound core vs. loosely bound valence electrons ( although they do not specifically relate to the Born energies).


M(g) + e- à M- (g)

Energy is typically released, meaning that the extra electron is typically stably bound in the anion and requires energy to get out. The energy change is typically a negative number.

Periodic Trends in Atomic Properties: Electron Affinity

There is a large range in values, and they follow periodic trends.

Particularly large for halogens (red)Particularly small (negative) for alkaline earth, noble

Many gas phase atoms are more stable after addition of electron; none is more stable after two electrons


+e-

+2e-

Negative


Unitless scale measuring the ability of an atom to attract electrons within a moleculeExample: HCl. There is a large difference in electronegativity comparing H and Cl, suggesting that some charge/electrons

will be transferred from H to Cl

Mulliken Definition: Average IE and EA

k: normalization, the highest value is 4 for F.

There are other definitions as weel, for example based on bond energies

k IE1 + EA1( )

Periodic Trends in Atomic Properties: Electronegativity

Periodic Trends in Atomic Properties: ElectronegativityThis table will not be given on Exam 2. Don’t memorize them, learn the trends!

Electronegative: small radius, nuclear charge attracts electrons strongly within a molecule. Example -- O

Electropositive: large radius, nuclear charge does not attract electrons strongly within a molecule. Example—alkali metals

Periodic: Increase from left to right, from bottom to top (except d-block). Not useful/well defined for noble gasses.

Periodic Trends in Atomic Properties: Electronegativity

Tendency of Metals and Halogens to Lose or Gain Electrons and Make Noble Gas Configurations

• Alkali metals lose a single electron and achieve a Noble Gas (Inert) Configuration

Csà Cs+ + e-

• Halogens gain a single electron and achieve a Noble Gas (Inert) Configuration

F + e- àF-

Na: [Ne]3sK: [Ar]4s

F: [He]2s22p5

Cl: [Ne] 3s23p5


Alkali Metals

Cs + H2O à ½ H2 + M+ + OH-

• Vigorous reaction• http://www.youtube.com/watch?v=uixxJtJP

VXk&feature=related


Nonmetal Halogens

F2 + H2 à 2 H F

Ionic: H+ and F-

• http://www.youtube.com/watch?v=u2ogMUDBaf4


“Crystal” Ionic Radii from X-ray Diffraction Studies

• Ions may be larger or smaller than the neutral atom, depending on the ion's electric charge.

• When an atom loses an electron to form a cation, the other electrons are more strongly attracted to the nucleus, and the radius of the atom gets smaller. Similarly, when an electron is added to an atom, forming an anion, the added electron increases the size of the electron cloud.

Periodic Trends in Atomic Properties: Atomic and Ionic Radii

• Your text gives a table 12.38 p 491 of the radii of neutral atoms.

• Each new shell is associated with a jump in size, going down the groups

• Going across the row the increase in charge is associated with a reduced radius.

Periodic Trends in Atomic Properties: Neutral Atom Radii

Periodic Trends in Atomic Properties: Ionic Radii

From UCSB

Discontinuity where charge changes.

Problem 93

• One bit of evidence that the quantum mechanical model is “correct” lies in the magnetic properties of matter. Atoms with unpaired electrons are attracted by magnetic fields and thus are said to exhibit paramagnetism or be paramagnetic. • The degree to which this effect is observed is directly

related to the number of unpaired electrons present in the atom. Consider the ground-state electron configurations for Li, N, Ni, Te, Ba, and Hg. Which of these atoms would be expected to be paramagnetic, and how many unpaired electrons are present in each paramagnetic atom?

Periodic Trends in Atomic Properties: Magnetism

Strategy: consider the electronic structure of the valence electrons.Example Ni Z=28 is between these two noble configurations

Ar 1s2 2s2 2p6 3s2 3p6: 18 electronsKr 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6: 36 electrons

Neutral Ni: [Ar] with 10 additional electrons.Following Aufbau, the configuration for Ni is: [Ar]4s23d8

Focus on “d8”. (In the 4th row or period, the exceptions are Cr and Cu.)

à To know if the 8 3d electrons are paired,apply Hund’s rule: the lowest energy configuration

has as many unpaired electrons as possible


Problem 93Periodic Trends in Atomic Properties: Magnetism

Periodic Trends in Atomic Properties: Magnetism

• Having the same electronic configuration• Example: Ne, F- and Na+• In this example all three have 10 electrons with a

“Noble” electronic configuration1s2 2s2 2p6

• Special stability is generally observed for electronic configurations with eight electrons in the valence shell, i.e. a complete s and p orbitals for the period or row, i.e. isoelectronic with a noble gas

Isoelectronic Atoms and Ions

Which set of atoms and ions is isoelectronic?

A) Na+,K+,Rb+

B) Cl-, K+, Ca2+

C) Ne, F, and NaD) Cl-, Cl, Cl+

E) Ar, Cl-, Na+

Question 70

Which set of atoms and ions is isoelectronic?

A) Be2+, Mg2+, Ca2+

B) Sc, Ti, VC) O, C2-, N-, F+

D) K-, K, K+

E) Ne, Ar, Kr

Question 71

Radial Probability Density for Electrons in Na Atom: Shielding of n=3 by n-1 and n=2.

The core electrons (n=1 and n=2) are in grey. For the most part they are really �inside� the n=3 shell. In a crude model the n=3 electrons see a central charge that consists of the nuclear charge (+11) and the core electrons (-10). In other words picture roughly that a neutral, small Ne atom is inside. We will use this later to make a model for a lead atom for example.

Approximation: Z effective or Zeff

The valence electrons feel the net charge including the core electrons plus the nucleus together (a screened nucleus).

For all neutral alkali Zeff = Z-C=1. For Ne and Ar Zeff = Z-C=8.

Note dramatic difference between Alkali and Noble ionizations energies.

Can we use the Born energies with Zeff, and the true n value?

E~ -(Zeff2/n2)R

Approximation: Z effective or Zeff

Estimates for ZeffEffective Z is less that the actual charge.

Empirical from the IE ~ (Zeff2/n2)R

Effective Z crude estimate by simplest approach : Zeff = Z-C. Subtract the number of core electrons from Z. Let’s use this first

Effective Z using “Slater’s Rules”• electrons within same group shield 0.35, except the 1s which shield 0.30• s or p electrons within the n-1 group shield 0.85• d or f electrons within the n-1 group shield 1.0• electrons within the n-2 or lower groups shield 1.0

Zeff for PWhat is the value for Zeff for the outer electrons of a neutral P atom from the simple model?

Z=15. [Ne] with 10 electrons is the relevant next smaller noble core. The configuration is [Ne]3s23p3.

The simple estimate for Zeff is 15- 10 = 5

From the Slater rules we obtain 15 - (2 + 8*.85 + 4*.35) = 4.8

Using Effective Z for PThe simple estimate for Zeff is 5 and the Slater rules we obtain 4.8.

We can predict the first ionization.

Using the first ionization energy of P, 1011 kJ/mol ~ (Zeff2/32)Rgives with Zeff = 2.63 for the 3p electron of P. Experimentally there is more shielding than these models.

This is a nice qualitative picture, and it predicts trends in ionization energies, but it is not generally quantitative!

• Use Z-C to estimate Z effective for Mg2+

• What would the value of n be for the most weakly bound electrons in Mg2+

Question 72

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