TRENDS IN THE PERIODIC TABLE

Important Definitions Trend: predictable change in a

particular direction Electron Shielding : inner electrons

shield outer electrons from the full attractive force of the nucleus

Effective Nuclear Charge (ENC): charge felt by the valence

electrons after you have

taken into account the

# of shielding electrons

Atomic RadiusAtomic radius: half of the

distance between the nuclei of two atoms of the same element bonded together.

Atomic Radius increases as you

move down a groupelectrons occupy consecutively higher energy levels, farther from the nucleus

ENC decreases due to increased shielding

H

Li

Na

K

Rb

Atomic Radiusdecreases as you move

across a periodElectrons are in the same energy

level there is more nuclear charge.Outermost electrons are pulled

closer.Na Mg Al Si P S Cl Ar

Atomic Radius Trends

Radius of Cations Metals form cations. Cations form by losing

electrons. Cations are smaller than the

atom they came from – not only do they lose electrons, they lose an entire energy level.

Radius of Anions Nonmetals form anions. Anions form by gaining

electrons. Anions are bigger than the

atom they came from – have the same energy level, and nuclear charge (ENC slightly smaller)

Ionic Radius Trends trends follow the same pattern

as atomic radius increases as you move down a

groupdue to decreased ENC (increased

shielding)

decreases as you move across a perioddue to increasing nuclear charge,

whether the ion is positive or negative

Ionic Radii Trends

Ionization Energy Ionization: removing an electron

from an atom or ion 1st Ionization energy: energy

required to remove an electron from an atom Must overcome attraction between

electron and nucleus

2nd Ionization Energy: The energy required to remove a second electron from a cation

I.E. for the 1st 10 elementsSymbol First Second Third

HHeLiBeBCNO F Ne

1312 2731 520 900 800 1086 1402 1314 1681 2080

5247 7297 1757 2430 2352 2857 3391 3375 3963

11810 14840 3569 4619 4577 5301 6045 6276

Why did these values increase so much?

Ionization Energy Group 1: easily loses its 1

valence electron Low first ionization energy Second ionization energy will be

very high since it now has a stable octet.

Group 2: easily lose 2 valence electrons Low first and second ionization

energies High third ionization energy

Ionization

Ionization Energy Trendsdecreases as you move

down a groupdue to electron shielding (decreasing ENC)

increases as you move across a perioddue to the increase in nuclear charge

Ionization Energy Trends

Electron Affinity Electron Affinity: the energy

given off when an electron is added to an atom to make an anion. elements with high electron

affinities form negative ions in ionic compounds.

elements with low electron affinities form positive ions in ionic compounds.

Electron Affinity Trendssame as for ionization

energydecreases as you move

down a group due to increased electron shielding (decrease in ENC)

increases as you move across a period due to increasing nuclear charge

Electron Affinity Trends