7_PeriodicTrends
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Transcript of 7_PeriodicTrends
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Periodic Trends
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Definition: Half of the distancebetween nuclei in covalently bondeddiatomic molecule
Radius decreases across a period Increased effective nuclear chargedue to decreased shielding
Radius increases down a group
Each row on the periodic table addsa shell or energy level to the atom
Atomic Radius
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Table of
AtomicRadii
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Period Trend:Atomic Radius
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Increases for successive electrons taken fromthe same atomTendsto increase across a period
Electrons in the same quantum level do notshield as effectively as electrons in inner levels
Irregularities at half filled and filledsublevels due to extra repulsion of electrons
paired in orbitals, making them easier toremove
Tendsto decrease down a group Outer electrons are farther from thenucleus and easier to remove
Ionization EnergyDefinition: the energy required to remove anelectron from an atom
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Ionization Energy: the energy required toremove an electron from an atom
Increases for successive electrons taken from the
same atom Tends to increase across a period
Electrons in the same quantum level do notshield as effectively as electrons in inner
levelsIrregularities at half filled and filledsublevels due to extra repulsion of electronspaired in orbitals, making them easier to
remove Tends to decrease down a group
Outer electrons are farther from the nucleus
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Table of 1st IonizationEnergies
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Periodic Trend:Ionization Energy
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Affinity tends to increase across a period
Affinity tends to decrease as you go
down in a periodElectrons farther from the nucleusexperience less nuclear attraction
Some irregularities due to repulsiveforces in the relatively small porbitals
Electron Affinity
Definition - the energy change associatedwith the addition of an electron
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Periodic Trend:Electron Affinity
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ElectronegativityDefinition: A measure of the ability of an
atom in a chemical compound to attractelectrons
o Electronegativity tends to increase
across a periodo As radius decreases, electrons getcloser to the bonding atoms nucleus
o Electronegativity tends to decrease
down a group or remain the sameo As radius increases, electrons arefarther from the bonding atomsnucleus
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Periodic Table of Electronegativities
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Periodic Trend:Electronegativity
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Summary ofPeriodic Trends
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Ionic Radii
Cations
Positively charged ions formed whenan atom of a metal loses one ormore electrons
Smaller than the corresponding
atom
Anions
Negatively charged ions formedwhen nonmetallic atoms gain one
or more electrons Larger than the corresponding
atom
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Tableof Ion
Sizes