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