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Shielding Effect protectioncore lessensvalenceThe protection provided by the inner core electrons which lessens the nucleus’s pull on the outer valence electrons Across a perioddoes not play outermostAcross a period, it does not play a significant role (all elements in a period have valence electrons in the same outermost energy level). Down a family significant core valence awayDown a family, it plays an increasingly more significant role (each family member has an additional layer of core electrons, moving the valence electrons further away from the nucleus).
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Periodic TrendsPeriodic Trends
Periodic TrendsPeriodic Trends• describe characteristicscharacteristics of elements across
periods and among families • are not absoluteabsolute – represent general trends • are based largely on the “shielding effectshielding effect”
Shielding EffectShielding Effect• The protectionprotection provided by the inner corecore
electrons which lessenslessens the nucleus’s pull on the outer valencevalence electrons
• Across a periodAcross a period, it does not playdoes not play a significant role (all elements in a period have valence electrons in the same outermost outermost energy level).
• Down a familyDown a family, it plays an increasingly more significantsignificant role (each family member has an additional layer of corecore electrons, moving the valence valence electrons further awayaway from the nucleus).
Atomic RadiusAtomic Radius
DefinitionDefinition: half the distance between the nuclei of like atoms in a solid TrendTrend: decreases from left to right and increases from top to bottom
ElectronegativitElectronegativityy
DefinitionDefinition: measure of attraction an atom has for a unshared pair of electronsTrendTrend: increases from left to right and decreases from top to bottom (excluding noble gases)
Ionization EnergyIonization EnergyDefinitionDefinition: amount of energy needed to release an electron from a gaseous atomTrendTrend: increases from left to right and decreases from top to bottom
ReactivityReactivityMetals: Metals: are more reactive with small ionization energies, small electronegativity values, and large atomic radii-Trend: down and to the left Francium: most reactive metal
Nonmetals: Nonmetals: are more reactive with large ionization energies, large electronegativity values, and small atomic radii-Trend: up and to the right (excluding noble gases) Fluorine: most reactive nonmetal
ReactivityReactivity
Periodic Trends Periodic Trends ExamplesExamples
Which of the following is the largest atom: Li, Rb, or Fr? Fr
Periodic Trends Periodic Trends ExamplesExamples
Rank the following atoms by decreasing atomic radius: Cs, Pb, At. Cs Pb At
Periodic Trends Periodic Trends ExamplesExamples
Which of the following has the greatest ionization energy: Rb, Sr, I, or O? O
Periodic Trends Periodic Trends ExamplesExamples
Rank the following in order of increasing ionization energy: Cs, Bi, Rn, F.
Cs Bi Rn F
Periodic Trends Periodic Trends ExamplesExamples
Which of the following has the greatest electronegativity: Li, Cs, or K? Li
Periodic Trends Periodic Trends ExamplesExamples
Rank the following in order of decreasing electronegativity: Fr, As, F. F As Fr
Periodic Trends Periodic Trends ExamplesExamples
Which metal is more reactive, Cs or Ca?
Cs
Periodic Trends Periodic Trends ExamplesExamples
Which nonmetal is more reactive, C or N?
N