1. Periodic Trends

2. Atomic Size – Scientists use the distance from the center of the nucleus to the boundary of the surrounding electron cloud as the atomic radius.
Cause of trends –
Period: As you go across a row the atomic number(# of protons) increases but no increase in Shielding
Ex) A Na atom is larger than an Ar atom because 18 protons can pull on energy levels 1 through 3 with greater strength than 11 protons can. 

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4. Atomic Size – Scientists use the distance from the center of the nucleus to the boundary of the surrounding electron cloud as the atomic radius.
Group: As you go down a group the number of energy levels increases and shielding occurs. (the # protons increase but the energy levels also increase).
Ex) A Na atom is smaller than an Fr atom because energy level #3 is closer to the nucleus than energy level # 7

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6. What is shielding?

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9. Ionization Energy: the amount of energy required to remove an electron from an atom.
Cause of trends –
Period: Closer to 8… closer to being happy
Period Trend

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11. Ionization Energy: the amount of energy required to remove an electron from an atom.
Cause of trends –
Group:
Ex) A Na atom has a higher I.E. than a Fr atom, because Fr's electron is further from the nucleus...less proton pulling power...AND already has more Energy.
Group Trend

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13. Electronegativity (electron affinity): a measure of how well an atom can attract and hold an electron from another atom.

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15. proton strength increases across row but size of atom decreases
This results in the formation of an ion and it is the ionic radius that will dominate how well the atom can retain the electron.
Cause of trends – Row
proton strength increases across row but size of atom decreases
Period

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17. Ionic Size Gain electron → size increase Lose electron → size decrease
Anion – negative ion is larger than its neutral atom
Lose electron → size decrease
Cation – positive ion, are smaller than their neutral atom

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