7_periodictrends

7/28/2019 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

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