1. Periodic table trends

2. Trends in the periodic table:
Ionization Energy
Atomic Radii Ionic Radii Electron Affinity Electronegativity
Shielding

3. Background
04/10/99
Electrons can jump between shells (Bohr’s model supported by line spectra)
The electrons can be pushed so far that they escape the attraction of the nucleus
Losing an electron is called ionization
An ion is an atom that has either a net positive or net negative charge
Q: What would the charge be on an atom that lost an electron? Gained two electrons?
A: +1 (because your losing a -ve electron)
A: -2 (because you gain 2 -ve electrons)

4. IONIZATION ENERGY
04/10/99
Ionization energy is the energy required to remove one outer electron from an atom
increase across, decrease down ( ,  )
increase across due to the increasing nuclear charge – takes more energy to remove electrons since they are closer to full valence shells
decrease down due to electrons being further from the nucleus
1st ionization energy = energy required to remove 1st outermost electron
2nd ionization energy = energy required to remove 2nd outermost electron, etc.
once electrons are removed from a neutral atom, atom is now an ion
ion = atom or group of bonded atoms that has either a positive or negative charge

5. ATOMIC RADIUS and IONIC RADIUS
Atomic radius is the distance from the nucleus to the outer electron shell
decrease across, increase down (  ,  )
decrease across - atom has valence shell that is becoming full and electrons are being pulled closer to nucleus
increase down - has a lot more electrons so is a larger atom
Ionic radius is the distance from the nucleus to the outer electron shell
decrease across, increase down (  ,  )
cations are always SMALLER than the neutral atoms from which they are formed due to the loss of the outer shell electrons resulting in increased attraction by the nucleus
anions are always LARGER than the neutral atom because the nuclear attraction is less for increased number of electrons

6. Ionization energy vs. atomic number
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7. Atomic radius vs. atomic number
04/10/99

8. IONIZATION ENERGY vs. ATOMIC RADIUS
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IONIZATION ENERGY vs. ATOMIC RADIUS
As one increases, the other decreases
Ionization energy increases
Atomic radius decreases
And. . .
Ionization energy decreases
Atomic radius increases

9. Electron configuration of Na+ resembles Ne
04/10/99
11p+ 12n°
11p+ 12n°
10p+ 10n°
Na has 11 electrons
Na+ has 10 electrons
Ne has 10 electrons
Electron configuration of Na+ resembles Ne
Alkali metals become like noble gases
Radius increases because shells are added
Increased radius will make it easier to lose an electron because of greater distance between positive and negative charges

10. Li (enc = 1) Be (enc = 2) B (enc = 3) + + + + + + + + + + + +
Proton # increases. More protons means greater attraction between nucleus and outer electron thus higher ionization energy.
The greater attraction also means that outer electrons are brought closer to the nucleus, thus smaller atomic radius results.
04/10/99
Li (enc = 1)
Be (enc = 2)
B (enc = 3) + + + + + + + + + + + +

11. 04/10/99
ELECTRON AFFINITY
Electron affinity is energy associated with an atom gaining an electron.
increase across, decrease down (, )
decrease down due to a larger size of atom (they already have lots of electrons)
energy that accompanies the addition of an electron to a gaseous atom
F(g) e-  F-(g)
negative means the gain of an electron is favorable since energy is released
positive means the gain of an electron is unfavorable since energy is absorbed
it is highest in the top right where atoms are smallest with the greatest number of protons

12. ELECTRO-NEGATIVITY
Electro-negativity is a number that describes the relative ability of an atom (when bonded) to attract electrons.
the trend is the same as affinity for the same reason.
increase across, decrease down ( ,  )
The tendency for an atom to attract electrons to itself when chemically combined
Cs is the least and F is the most
noble gases are omitted because they do not form compounds

13. SHIELDING this is how well the nucleus is surrounded by electrons
remains constant across, increases down
(constant  ,  )
*****NOTE:
Ignore H when looking at trends, look at many periods/groups when summarizing trends
Noble gases are ignored since they already have a full outer, valence, shell.