AP Chemistry Chapter 6AP Chemistry Chapter 6

Electronic Structure and the Electronic Structure and the Periodic TablePeriodic Table

Nature of LightNature of Light

Wavelengths and frequenciesWavelengths and frequencies Wavelength – distance between “troughs”Wavelength – distance between “troughs”

Measured in meters or nanometerMeasured in meters or nanometer 1nm = 101nm = 10-9-9mm

Frequency – number of of wave cycles Frequency – number of of wave cycles that pass a given point in unit time that pass a given point in unit time Hertz – represents cycles per secondHertz – represents cycles per second Ex. If 10Ex. If 101010 cycles pass a particular point in one cycles pass a particular point in one

second v = 10second v = 101010 Hz Hz

λλv = cv = c c = speed of light in vacuumc = speed of light in vacuum 2.998 x 102.998 x 1088 m/s m/s λλ expressed in meters expressed in meters v in hertzv in hertz

Photon energiesPhoton energies

E = E = hchc

λλ

Use to determine energy in joules of a Use to determine energy in joules of a photon emitted by an excited atomphoton emitted by an excited atom

Also use to determine energy, in joules, of a Also use to determine energy, in joules, of a mole of photonsmole of photons

multiple by 6.02 x 10multiple by 6.02 x 102323

Remember to convert to kilojoules if Remember to convert to kilojoules if necessary!!!necessary!!!

101033J = 1 kJJ = 1 kJ

Bohr modelBohr model

Based on the hydrogen atomBased on the hydrogen atom Why the electrons that were circling the Why the electrons that were circling the

nucleus did not release their energy and nucleus did not release their energy and spiral into the nucleusspiral into the nucleus

He calculated energies associated with He calculated energies associated with each allowed orbiteach allowed orbit

EEnn = = -2.178 x 10-2.178 x 10-18-18 JJ

nn22

EEnn = energy of the electron = energy of the electron

n = principal energy leveln = principal energy level

This formula is included on AP constants This formula is included on AP constants sheetsheet

Quantum Mechanical Model of Quantum Mechanical Model of electron placementelectron placement

First quantum number, nFirst quantum number, ndesignates Principal designates Principal

Quantum LevelQuantum Levelmust be an integermust be an integerImportant for determining Important for determining

energy of the electronenergy of the electron

ll = Second Quantum Number = Second Quantum Number

Determines shape of electron cloudDetermines shape of electron cloud l = l = 0, 1,2,3……(n-1)0, 1,2,3……(n-1)

nn = 1 = 1 l = l = 0 0 n = 2 n = 2 l l = 0, 1= 0, 1 nn = 3 = 3 l l = 0,1,2= 0,1,2 n = 4n = 4 l l = 0,1,2,3= 0,1,2,3

mmll = Third Quantum Number= Third Quantum Number

Determines electrons orientation in spaceDetermines electrons orientation in space Corresponds to number of orbitals allowed in Corresponds to number of orbitals allowed in

that sublevel (that sublevel (ll))

ll = 0 m = 0 m ll = 0 = 0 (1 orbital)(1 orbital)

ll = 1 m = 1 m ll = 1,0,-1 = 1,0,-1 (3 orbitals)(3 orbitals)

ll = 2 m = 2 m ll = 2,1,0,-1,-2 = 2,1,0,-1,-2 (5 orbitals)(5 orbitals)

ll = 3 m = 3 m ll = 3,2,1,0,-1,-2,-3 = 3,2,1,0,-1,-2,-3 (7 orbitals)(7 orbitals)

MMss = Fourth Quantum Number; = Fourth Quantum Number;

electron spinelectron spin Electron has magnetic properties like that Electron has magnetic properties like that

of charged particles spinning on an axisof charged particles spinning on an axis Either of two spins is possible – clockwise Either of two spins is possible – clockwise

or counterclockwiseor counterclockwise +1/2 -1/2+1/2 -1/2

Electrons with different mElectrons with different mss values values

(one +1/2 and the other -1/2)(one +1/2 and the other -1/2) Said to have “Said to have “opposedopposed” spins” spins

Electrons with same value for mElectrons with same value for mss

(both +1/2 or -1/2)(both +1/2 or -1/2) Said to have “Said to have “parallelparallel” spins” spins

Pauli Exclusion PrinciplePauli Exclusion Principle

No two electrons in an atom can No two electrons in an atom can have the same set of four have the same set of four quantum numbersquantum numbers

If they occupy the same orbital, If they occupy the same orbital, must have opposing spinsmust have opposing spins

Pg. 140 example 6.4, 6.5Pg. 140 example 6.4, 6.5

Review shape of sublevelsReview shape of sublevels s - sphere, p - figure-8s - sphere, p - figure-8

Pg. 412 shape of d sublevel orbitalsPg. 412 shape of d sublevel orbitals

Hund’s RuleHund’s Rule

When several orbitals of equal When several orbitals of equal energy are available, as in a energy are available, as in a given sublevel, electrons enter given sublevel, electrons enter singly with parallel spinssingly with parallel spins

Solids – is possible to determine number Solids – is possible to determine number of unpaired electrons in an atom by their of unpaired electrons in an atom by their behavior in a magnetic fieldbehavior in a magnetic field

If unpaired electrons are present, the solid If unpaired electrons are present, the solid will be attracted into the fieldwill be attracted into the field That substance called That substance called

““paramagneticparamagnetic””

If the atoms in the solid contain only If the atoms in the solid contain only paired electrons, is slightly repelled paired electrons, is slightly repelled by the fieldby the field Called “Called “diamagneticdiamagnetic””

Review electron configurations and Review electron configurations and orbital notationorbital notation

Aufbau PrincipleAufbau Principle Sublevels are filled in order of Sublevels are filled in order of

increasing energyincreasing energy Stability exceptions: Cr, Mo, W, Cu, Ag, Stability exceptions: Cr, Mo, W, Cu, Ag,

AuAu

• break from strict Aufbau Principlebreak from strict Aufbau Principle

Review “blocks” on Periodic TableReview “blocks” on Periodic Table Lanthanides – filling 4Lanthanides – filling 4ff Actinides – filling 5Actinides – filling 5f (all of these f (all of these

elements are radioactive, only elements are radioactive, only thorium and uranium are found thorium and uranium are found in naturein nature Stability decreases with increasing Stability decreases with increasing

atomic numberatomic number

Monatomic ionsMonatomic ions

Electrons are added to or removed Electrons are added to or removed from sublevels in the highest principal from sublevels in the highest principal energy levelenergy level

Want to achieve configuration like a Want to achieve configuration like a noble gas – more stablenoble gas – more stable

Na+1 (1sNa+1 (1s222s2s222p2p66) + e) + e--

Species (whether ion or not) Species (whether ion or not) with same electron with same electron configuration called configuration called ““isoelectronicisoelectronic””

Transition Metal CationsTransition Metal Cations

When transition metals from positive ions, When transition metals from positive ions, the outer s electrons are lost firstthe outer s electrons are lost first

2525Mn Mn [Ar] 4s[Ar] 4s223d3d55 to to

MnMn+2 +2 [Ar]3d [Ar]3d55

After the outer s electrons are lost, then After the outer s electrons are lost, then the d can be lostthe d can be lost

2626Fe Fe [Ar]4s[Ar]4s223d3d66 forms Fe forms Fe+3+3

[Ar]3d[Ar]3d55 ““first in, first out” rulefirst in, first out” rule

Periodic TrendsPeriodic Trends

Atomic Radius – one half the distance Atomic Radius – one half the distance of closest approach between atoms in of closest approach between atoms in an elemental substance (pg. 151 an elemental substance (pg. 151 drawing)drawing) Decreases across a period from left Decreases across a period from left

to rightto right Increases down a group as atomic Increases down a group as atomic

number increasesnumber increases

In a group, are increasing one whole In a group, are increasing one whole pel as you go downpel as you go down The inner electrons “shield” the The inner electrons “shield” the

outer electrons from the positive outer electrons from the positive nucleusnucleus

In periods, inner electrons are a poor In periods, inner electrons are a poor “shield” because they are at about the “shield” because they are at about the same distance from the nucleussame distance from the nucleus

Period trend continuedPeriod trend continued

Effective nuclear chargeEffective nuclear charge (charge felt (charge felt by an outer electron) increases by an outer electron) increases steadily with atomic numbersteadily with atomic number

As As effective nuclear chargeeffective nuclear charge increases, the outermost electrons increases, the outermost electrons are pulled in more tightly, and atomic are pulled in more tightly, and atomic radius decreasesradius decreases

Ionic RadiusIonic Radius

Increases moving down a groupIncreases moving down a group Both cations and anions decrease Both cations and anions decrease

from left to right across a periodfrom left to right across a period Positive ions smaller that their atomsPositive ions smaller that their atoms Negative ions larger than their atomsNegative ions larger than their atoms Pg. 152 Figure 6.13Pg. 152 Figure 6.13

Cation Cation – excess of protons draws the outer – excess of protons draws the outer electrons closerelectrons closer

Anion Anion – extra electron adds to the repulsion – extra electron adds to the repulsion between outer electrons (makes the negative ion between outer electrons (makes the negative ion larger that the corresponding atom)larger that the corresponding atom)

Pg. 153 example 6.10Pg. 153 example 6.10

Ionization EnergyIonization Energy

Measure of how difficult it is to remove an Measure of how difficult it is to remove an electron from a gaseous atomelectron from a gaseous atom

Energy must always be absorbed to Energy must always be absorbed to remove an electron, so always a positive remove an electron, so always a positive quantityquantity

First ionization energy – removal of First ionization energy – removal of outermost electronoutermost electron

XX(g)(g) X X++ + e + e--

ΔΔEE11 = first ionization energy = first ionization energy

TrendsTrends

Increases across a period (left to right)Increases across a period (left to right) Decreases down a group (increasing a.n.)Decreases down a group (increasing a.n.) Indirect relationship between atomic radius Indirect relationship between atomic radius

and ionization energyand ionization energy Large atom, electron far from the nucleus, Large atom, electron far from the nucleus,

easier to removeeasier to remove Smaller atom, electrons closer to the nucleus, Smaller atom, electrons closer to the nucleus,

held tighter, so harder to removeheld tighter, so harder to remove

Pg. 153 Figure 6.15Pg. 153 Figure 6.15 First ionization energies in kJ/molFirst ionization energies in kJ/mol

Pg. 154 Example 6.11Pg. 154 Example 6.11

ElectronegativityElectronegativity

Measure the ability of an atom in a Measure the ability of an atom in a molecule to attract electrons to itselfmolecule to attract electrons to itself

The greater the electronegativity, the The greater the electronegativity, the greater is its ability to attract electrons to greater is its ability to attract electrons to itselfitself

Dependent on ionization energy and Dependent on ionization energy and electron affinityelectron affinity

Electron affinity – tendency to form anionsElectron affinity – tendency to form anions EA = energy required to add an electronEA = energy required to add an electron Z + eZ + e- - + energy + energy Z Z--

EA = energy released on removing e- fromEA = energy released on removing e- from

anionanion ZZ-- Z + e Z + e-- + energy + energy

If EA is large and negative, the atom If EA is large and negative, the atom “wants” to add an electron and form an “wants” to add an electron and form an anionanion

Atom with a very negative electron affinity Atom with a very negative electron affinity and a high ionization energy will attract eand a high ionization energy will attract e-- and resist any eand resist any e-- being removed from it. being removed from it.

Is highly Is highly electronegativeelectronegative

EN TrendsEN Trends

Period – generally a steady increase Period – generally a steady increase (metal to nonmetal)(metal to nonmetal)

Group – decrease within a group (are Group – decrease within a group (are some exceptions) some exceptions)

Scale of electronegativities pg. 154Scale of electronegativities pg. 154 Important scale when we get to bonding!Important scale when we get to bonding!