trends in the periodic table. important definitions trend : predictable change in a particular...
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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
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