Periodic TrendsPeriodic Trends

Trends in Properties on the Trends in Properties on the Periodic TablePeriodic Table

The PlanThe Plan

Essential Question: What causes the trends Essential Question: What causes the trends of the properties in the periodic table?of the properties in the periodic table?

Discuss Some Properties of AtomsDiscuss Some Properties of Atoms

Explore the TrendsExplore the Trends

Try to Explain the TrendsTry to Explain the Trends

Effective Nuclear ChargeEffective Nuclear Charge

Effective Nuclear Charge Effective Nuclear Charge - (Z- (Zeffeff) – the ) – the charge an electron “feels” from the charge an electron “feels” from the nucleusnucleus

ZZeffeff = Z – S, where Z is the atomic number = Z – S, where Z is the atomic number and S is the shielding experienced by the and S is the shielding experienced by the outer electronsouter electrons

The electrons in the outer energy levels The electrons in the outer energy levels don’t feel the full charge of the nucleus don’t feel the full charge of the nucleus because the core electrons help shield because the core electrons help shield them from the nucleus.them from the nucleus.

Atomic RadiusAtomic Radius

Atomic radiusAtomic radius – the – the radius of an atomradius of an atom

Several methods of Several methods of determining the determining the radius - usually radius - usually measure the distance measure the distance between two atomsbetween two atoms

Not all values are Not all values are completely consistent completely consistent with each other.with each other.

Ionization EnergyIonization Energy

Ionization EnergyIonization Energy – the energy required to – the energy required to remove one electron from an atomremove one electron from an atom

Essentially this is the process of making a Essentially this is the process of making a positive ion.positive ion.

X X X X++ + e + e--

ElectronegativityElectronegativity

ElectronegativityElectronegativity – the ability of an atom in – the ability of an atom in a compound to attract electrons to itselfa compound to attract electrons to itself

Electrons in compounds spend the most Electrons in compounds spend the most time around atoms with high time around atoms with high electronegativities.electronegativities.

Elements with high electronegativities Elements with high electronegativities have partial negative charges in have partial negative charges in compounds.compounds.

Periodic Trends LabPeriodic Trends Lab

In your lab groups, predict what trends you In your lab groups, predict what trends you think might occur down a family and think might occur down a family and across a period for each of the properties across a period for each of the properties we discussed:we discussed:

Effective nuclear chargeEffective nuclear chargeAtomic radiusAtomic radiusIonization energyIonization energyElectronegativityElectronegativity

Record on the index card for discussion laterRecord on the index card for discussion later

Effective Nuclear ChargeEffective Nuclear Charge

As you travel left to right across a period:As you travel left to right across a period:Atomic number increasesAtomic number increasesShielding stays roughly the sameShielding stays roughly the sameTherefore ZTherefore Zeffeff increases significantly across a increases significantly across a

periodperiodAs you travel down a familyAs you travel down a family

Atomic number increases sharplyAtomic number increases sharplyShielding increases sharplyShielding increases sharplyZZeffeff does increase down a family but not as does increase down a family but not as

much as you might expect.much as you might expect.

Atomic RadiusAtomic RadiusAs you travel left to right across a period:As you travel left to right across a period:

Effective nuclear charge increasesEffective nuclear charge increasesElectrons are being added to the same n shellElectrons are being added to the same n shelln values have somewhat to do with distance n values have somewhat to do with distance

from the nucleus.from the nucleus.Size of atoms shrink as you move to the right.Size of atoms shrink as you move to the right.

As you travel down a familyAs you travel down a familyEffective nuclear charge increases more Effective nuclear charge increases more

slowlyslowlyElectrons are added to n shells farther awayElectrons are added to n shells farther awaySize of atoms increase down the familySize of atoms increase down the family

Ionization EnergyIonization Energy

As you travel left to right across a periodAs you travel left to right across a periodEffective nuclear charge increasesEffective nuclear charge increasesHarder to remove an electron therefore…Harder to remove an electron therefore… Ionization Energy increasesIonization Energy increases

As you travel down a familyAs you travel down a familyEffective nuclear charge increases slowlyEffective nuclear charge increases slowlyOuter electrons are farther away from the Outer electrons are farther away from the

nucleusnucleus Ionization Energy decreasesIonization Energy decreases

Ionization EnergyIonization Energy

Ionization EnergyIonization Energy

ElectronegativityElectronegativity

As you travel left to right across a period:As you travel left to right across a period:Effective nuclear charge increases stronglyEffective nuclear charge increases stronglyElectronegativity increasesElectronegativity increases

As you travel down a familyAs you travel down a familyEffective nuclear charge increases slowlyEffective nuclear charge increases slowlyOuter electrons are being added in shells Outer electrons are being added in shells

farther and farther awayfarther and farther awayElectronegativity decreasesElectronegativity decreases

ElectronegativityElectronegativity

Ionic RadiusIonic Radius

Ionic RadiusIonic Radius – size of an ion – size of an ion

Consider two different relationshipsConsider two different relationshipsRelationship between atom and ionRelationship between atom and ionRelationship between ions and atoms with the Relationship between ions and atoms with the

same number of electronssame number of electrons““isoelectronic series”isoelectronic series”

Ionic RadiusIonic Radius

Ionic vs. AtomicIonic vs. Atomic

Number of protons always stays the sameNumber of protons always stays the sameFor negative ions (anions)For negative ions (anions)

Electrons are added to the same outer shellElectrons are added to the same outer shellElectron-electron repulsions increaseElectron-electron repulsions increaseAnions are larger than their atomsAnions are larger than their atoms

For positive ions (cations)For positive ions (cations)Electrons are removed to leave one less shellElectrons are removed to leave one less shelln shells describe distance from nucleusn shells describe distance from nucleusCations are smaller than their atomsCations are smaller than their atoms

Ionic RadiusIonic Radius

Isoelectronic seriesIsoelectronic series

All have the same number of electronsAll have the same number of electronsNumber of protons changesNumber of protons changesTherefore effective nuclear charge Therefore effective nuclear charge

increasesincreasesElectrons are pulled in tighterElectrons are pulled in tighterThe negative ions are larger than the The negative ions are larger than the

positive ions with the same number of positive ions with the same number of electrons.electrons.

Practice ProblemsPractice Problems

Arrange the following elements in order of Arrange the following elements in order of decreasing atomic radius:decreasing atomic radius:As, O, Sn, Ge, Ne, Ba, HeAs, O, Sn, Ge, Ne, Ba, He

Arrange the following elements in order of Arrange the following elements in order of increasing electronegativityincreasing electronegativityAl, Mg, P, Sr, O, F, RbAl, Mg, P, Sr, O, F, Rb

Ticket Out the DoorTicket Out the Door

Arrange the following elements in order of Arrange the following elements in order of increasing ionization energy:increasing ionization energy:Cs, Ba, Y, In, Ga, Si, P, FCs, Ba, Y, In, Ga, Si, P, F

Test Review ProblemTest Review Problem

Challenge ProblemChallenge ProblemPlace the following in order of increasing Place the following in order of increasing

size: Ne, Clsize: Ne, Cl--, Ar, Na, Ar, Na++