Dmitri Mendeleev

“The elements, if arranged according to their atomic weights, exhibit an apparent periodicity of properties.”

Periodic Trends

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Atomic Radius

1. Atomic Radius

Across PeriodAtomic size DECREASESBecause nuclear charge (# p+) increases, as e- are added to same n, pulls e- in tighter

Down GroupAtomic size INCREASESBecause more n (shells), more shielding,

e- further away from nucleus

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Electronegativity

2. Electronegativity

The ability to attract e-

Across PeriodEN INCREASESBecause nuclear charge (# p+) increases

Down GroupEN DECREASESBecause more n, more shielding, e- further

away from nucleus

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Ionization Potential

3. Ionization Potential/EnergyIE: Energy required to remove e-

Higher the IE: more difficult to remove e-

Across PeriodIE INCREASES** with decrease @ each subshellWhy?

Down GroupIE DECREASESWhy?

4. Ionic Radius

Ion-Charged atom

CationPositive (+) ion (neutral atom looses e-)

AnionNegative (-) ion (neutral atom gains e-)

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Ionic Radius

4. Ionic Radius

Across PeriodIR DECREASES** with jump up in size @ metalloids

Down GroupIR INCREASESCompare to neutral atom Ex. Br

Valence e- are the outermost e- of an atom

5. Metallic Properties

Across PeriodMP DECREASES

Down GroupMP INCREASES