Periodic PropertiesPeriodic Properties

Valence ElectronsValence ElectronsValence electronsValence electrons

– Electrons in the – Electrons in the outer energy level outer energy level that can be lost, that can be lost, gained, or shared gained, or shared (connected to the (connected to the group #)group #)

Group #Group # Valence eValence e--

11 1122 22

1313 331414 441515 551616 661717 771818 88

Atomic RadiiAtomic Radii• The atomic radius is a measure of the size

of an atom (½ distance betw 2 nuclei).• The larger the radius, the larger is the

atom.• http://www.mhhe.com/physsci/chemistry/essenti

alchemistry/flash/atomic4.swf• http://www.youtube.com/watch?v=YS71PbwUPx

8

Atomic RadiiAtomic Radii

Atomic RadiiAtomic RadiiRadii Radii decrease across a perioddecrease across a period

because the nucleus gets a larger because the nucleus gets a larger positive chargepositive charge

Radii Radii increase down a groupincrease down a group because because the nucleus gets largerthe nucleus gets larger

Which is larger and why? Which is the Which is larger and why? Which is the smallest? Li, O, C, or Fsmallest? Li, O, C, or F

Largest: LiLargest: Li Smallest: FSmallest: FWhat about Be, Mg, Ca, or Sr?What about Be, Mg, Ca, or Sr?Largest: Sr Largest: Sr Smallest: BeSmallest: Be

Ionization EnergyIonization Energy IonIon – an atom that has a positive or – an atom that has a positive or

negative chargenegative charge IonizationIonization – process that results in – process that results in

forming an ionforming an ion Ionization energy (IE)Ionization energy (IE) – energy required – energy required

to remove one electron from a neutral to remove one electron from a neutral atom (energy needed to make a positive atom (energy needed to make a positive charge)charge)

Ionization EnergyIonization Energy

A + EnergyA + Energy AA++ + e + e--

•IE increases across a period because the nuclear charge increases (more electrons in the orbitals)

•IE decreases down a group because it is easier to remove e- from higher energy levels

Electron AffinityElectron Affinity

Electron Affinity (EA)Electron Affinity (EA) – energy – energy needed to add an electron to a needed to add an electron to a neutral atom (opposite of IE).neutral atom (opposite of IE).

A + e- A- + energy

Electron AffinityElectron Affinity

EA decreases across periodsEA decreases across periods (get (get more negative)more negative)

EA decreases down groupsEA decreases down groups as as nuclear charge increases.nuclear charge increases.

***There are many exceptions to this ***There are many exceptions to this rule!!!rule!!!

Ionic RadiiIonic RadiiCationCation – positive ion (decrease in atomic – positive ion (decrease in atomic

radii)radii)Anion Anion – negative ion (increase in atomic – negative ion (increase in atomic

radii)radii) Ionic radii Ionic radii decrease across periodsdecrease across periods

because the electron cloud shrinksbecause the electron cloud shrinks Ionic radii Ionic radii increase down groupsincrease down groups as as

energy levels increaseenergy levels increase

ElectronegativityElectronegativityElectronegativityElectronegativity -- the ability of an atom -- the ability of an atom

to attract electronsto attract electronsElectronegativities Electronegativities increase across a increase across a

period and decrease down groupsperiod and decrease down groups (but (but there are exceptions!)there are exceptions!)

**Fluorine is the most electronegative atom!!**Fluorine is the most electronegative atom!!

The Best Way to Remember….The Best Way to Remember….Just know all the trends that surround Just know all the trends that surround

Fluorine, and work your way down or Fluorine, and work your way down or across!across!

F – most electronegative, highest IE, F – most electronegative, highest IE, lowest EA, small atomic and ionic radiilowest EA, small atomic and ionic radii

All Periodic TrendsAll Periodic Trends