Periodic TrendsPeriodic Trends

Section 4.3Section 4.3

Ionization EnergyIonization Energy

The amount of energy The amount of energy needed to remove an outer needed to remove an outer electron from a specific electron from a specific atom or ionatom or ion

Ionization EnergyIonization Energy

The TrendThe Trend

It decreases down a groupIt decreases down a groupe- shieldinge- shielding - The reduction of - The reduction of the attractive force between a + the attractive force between a + nucleus and its outermost e- b/c nucleus and its outermost e- b/c of the cancellation of some of the of the cancellation of some of the + charge by – charge of the outer + charge by – charge of the outer e-e-

Ionization EnergyIonization Energy

Ionization energy increase Ionization energy increase across a periodacross a period

Adding e- to same level & Adding e- to same level & p+ can hold it tighterp+ can hold it tighter

Atomic Radius/RadiiAtomic Radius/Radii

Atomic radiusAtomic radius

Usually determined for atoms Usually determined for atoms bonded or close togetherbonded or close together

Bond radiusBond radius – ½ the distance – ½ the distance from center to center of two from center to center of two like atoms bonded togetherlike atoms bonded together

The TrendThe Trend

Atomic radius increases as Atomic radius increases as you move down a groupyou move down a group

Due to addition of principle E Due to addition of principle E levellevel

The e- in the middle E levels The e- in the middle E levels shield the outside e- from the shield the outside e- from the force of the nucleus.force of the nucleus.

TrendTrend

Atomic radius decreases as you Atomic radius decreases as you move across a periodmove across a periodDecreases b/c of increased + Decreases b/c of increased + chargecharge–You are adding an e- and a p+, You are adding an e- and a p+,

but the e-’s are going into the but the e-’s are going into the same E level and being pulled same E level and being pulled by the p+by the p+

Atomic RadiusAtomic Radius

As charge increases, the As charge increases, the effective nuclear charge effective nuclear charge increases alsoincreases also

This pulls e- closer to the This pulls e- closer to the nucleusnucleus

Overall, this reduces the size Overall, this reduces the size of the atomof the atom

Repulsive ForcesRepulsive Forces

Eventually, the e- will get Eventually, the e- will get close and repel each otherclose and repel each other

Here, the atom doesn’t get Here, the atom doesn’t get any smallerany smaller

Similar trend for ionic radiusSimilar trend for ionic radius

Atomic RadiiAtomic Radii

ElectronegativityElectronegativity

ElectronegativityElectronegativity – a measure of the – a measure of the ability of an atom in a chemical ability of an atom in a chemical compound to attract e-’scompound to attract e-’s

The higher the e-neg, the stronger The higher the e-neg, the stronger that atom will pull e-’s from other that atom will pull e-’s from other elementselements

ElectronegativityElectronegativity

Decreases as you go down a Decreases as you go down a groupgroup

Adding principle quantum #Adding principle quantum #

+ nucleus can’t pull e- as much + nucleus can’t pull e- as much b/c of e- shieldingb/c of e- shielding

E-negE-neg

Increases across a pd.Increases across a pd.

Effective nuclear charge is Effective nuclear charge is more of a factormore of a factor

Electron AffinityElectron Affinity

The energy emitted upon the The energy emitted upon the addition of an electron to a addition of an electron to a neutral atom in the gas phase.neutral atom in the gas phase.

Becomes more negative Becomes more negative across a periodacross a periodDecreases down a groupDecreases down a groupSimilar to e-neg.Similar to e-neg.

Melting and Boiling PointMelting and Boiling Point

Not as straight forward as Not as straight forward as the other trends.the other trends.

Change as the different Change as the different orbitals begin to fillorbitals begin to fill