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Periodic TrendsTrends in Properties on the Periodic Table
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The PlanEssential Question: What causes the trends of the
properties in the periodic table?
Discuss Some Properties of Atoms
Explore the Trends
Try to Explain the Trends
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Effective Nuclear ChargeEffective Nuclear Charge - (Zeff) the
charge an electron feels from the nucleusZeff = Z S, where Z is the
atomic number and S is the shielding experienced by the outer
electronsThe electrons in the outer energy levels dont feel the
full charge of the nucleus because the core electrons help shield
them from the nucleus.
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Atomic RadiusAtomic radius the radius of an atomSeveral methods
of determining the radius - usually measure the distance between
two atomsNot all values are completely consistent with each
other.
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Ionization EnergyIonization Energy the energy required to remove
one electron from an atom
Essentially this is the process of making a positive ion.X X+ +
e-
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ElectronegativityElectronegativity the ability of an atom in a
compound to attract electrons to itself
Electrons in compounds spend the most time around atoms with
high electronegativities.
Elements with high electronegativities have partial negative
charges in compounds.
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Periodic Trends LabIn your lab groups, predict what trends you
think might occur down a family and across a period for each of the
properties we discussed:Effective nuclear chargeAtomic
radiusIonization energyElectronegativityRecord on the index card
for discussion later
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Effective Nuclear ChargeAs you travel left to right across a
period:Atomic number increasesShielding stays roughly the
sameTherefore Zeff increases significantly across a periodAs you
travel down a familyAtomic number increases sharplyShielding
increases sharplyZeff does increase down a family but not as much
as you might expect.
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Atomic RadiusAs you travel left to right across a
period:Effective nuclear charge increasesElectrons are being added
to the same n shelln values have somewhat to do with distance from
the nucleus.Size of atoms shrink as you move to the right.As you
travel down a familyEffective nuclear charge increases more
slowlyElectrons are added to n shells farther awaySize of atoms
increase down the family
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Ionization EnergyAs you travel left to right across a
periodEffective nuclear charge increasesHarder to remove an
electron thereforeIonization Energy increasesAs you travel down a
familyEffective nuclear charge increases slowlyOuter electrons are
farther away from the nucleusIonization Energy decreases
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Ionization Energy
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Ionization Energy
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ElectronegativityAs you travel left to right across a
period:Effective nuclear charge increases stronglyElectronegativity
increasesAs you travel down a familyEffective nuclear charge
increases slowlyOuter electrons are being added in shells farther
and farther awayElectronegativity decreases
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Electronegativity
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Ionic RadiusIonic Radius size of an ion
Consider two different relationshipsRelationship between atom
and ionRelationship between ions and atoms with the same number of
electronsisoelectronic series
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Ionic Radius
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Ionic vs. AtomicNumber of protons always stays the sameFor
negative ions (anions)Electrons are added to the same outer
shellElectron-electron repulsions increaseAnions are larger than
their atomsFor positive ions (cations)Electrons are removed to
leave one less shelln shells describe distance from nucleusCations
are smaller than their atoms
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Ionic Radius
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Isoelectronic seriesAll have the same number of electronsNumber
of protons changesTherefore effective nuclear charge
increasesElectrons are pulled in tighterThe negative ions are
larger than the positive ions with the same number of
electrons.
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Practice ProblemsArrange the following elements in order of
decreasing atomic radius:As, O, Sn, Ge, Ne, Ba, He
Arrange the following elements in order of increasing
electronegativityAl, Mg, P, Sr, O, F, Rb
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Ticket Out the DoorArrange the following elements in order of
increasing ionization energy:Cs, Ba, Y, In, Ga, Si, P, F
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Test Review ProblemChallenge ProblemPlace the following in order
of increasing size: Ne, Cl-, Ar, Na+
