Periodicity

1
The Periodic Table
Understanding the Periodic Nature of the Elements
2
Historical Development of the Periodic Table
3
DETERMINING THE RADIUS OF AN ATOM
?
?
Br2 2.286 A (1.14 A)
?
?
C-C 1.54 A (0.77 A)
?
C-Br 1.91 A
4
TRENDS IN ATOMIC SIZE
Atomic size correlates to the number of energy
levels (n) in an atom and the effective nuclear
charge (Z eff) of that atom
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Li1s22s1
n 2, Z eff 1
n 3, Z eff 1
Na1s22s22p63s1
n 3, Z eff 2
Be1s22s2
n 2, Z eff 2
Mg1s22s22p63s2
n 3, Z eff 3
O1s22s22p63s23p1
n 2, Z eff 3
B1s22s22p1
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IONIZATION ENERGY (I1,2,n)
The energy required to remove an electron from a
gaseous atom M(g) ? M(g) e-
Si
2s2
1s2
2p6
3s2
3p2
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Ionization energy increases from left to right
across a period
Ionization energy decreases going down a group
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These 2e- do a better job of shielding the
2p1 electron than they do of shielding each other
Be1s22s2
n 2, Z eff 2
2s2
1s2
n 2, Z eff 3
B1s22s22p1
2p1
2s2
1s2
? decrease in I1
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These 2e- repel one another
N1s22s22p3
n 2, Z eff 5
2s2
1s2
n 2, Z eff 3
O1s22s22p4
2p1
2s2
1s2
? decrease in I1
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ELECTRON AFFINITY (E a)
The energy change that occurs when an electron is
added to a gaseous atom M(g) e- ? M-
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ELECTRON AFFINITY (E a)
The energy change that occurs when an electron is
added to a gaseous atom M(g) e- ? M-

• Adding one or more electrons is an exothermic
  process for most neutral atoms and for all
  positively charged ions.

• Adding one or more electrons is an endothermic
  for process for some neutral atoms and for all
  negatively charged anions ions.

• The greater the attraction between the species
  and the added electron, the more negative the
  electron affinity.

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Electron affinity generally increases from left
to right across the periodic table
Electron affinity undergoes very little change
going down a group
Note that VA elements are less negative (dont
attract electrons as well as) IVA elements
C1s22s22p2
n 2, Z eff 4
N1s22s22p3
n 2, Z eff 5
Adding this electron would increase the
electron-electron repulsion and reduce the
electron-nucleus attraction for the added electron
? less negative Ea
In general, atoms with filled or half-filled
subshells have more positive electron affinities
than do elements on either side of them in the
periodic table
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• Nonmetallic Elements
• Nonlusterous
• Solids are brittle
• Most nonmetal oxides are acidic
• Exist in solution as cations.

• Metallic Elements
• Distinguishing luster
• Good thermal and electrical conductivity
• Most metallic oxides are basic
• Exist in solution as cations.

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Group Trends The Active Metals

• Alkali metals are prepared by passing an electric
  current (electrolysis)
• through molten salt

• Active metals are soft, possess low densities and
  low melting points

• Alkali metals possess the lowest ionization
  energies of the elements

• Alkali metals readily combine with most nonmetals

2M(s) H2 ? 2MH(s)
2M(s) S ? M2S(s)
2M(s) Cl2 ? 2MCl(s)

• Alkali metals react vigorously with water

2M(s) H2O ? 2MOH H2(g)

• Alkali metals react with oxygen to form oxides,
  peroxides, and superoxides

4Li(s) O2 ? 2Li2O
2Na(s) O2 ? 2Li2O2
K O2 ? KO2
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Group Trends The Alkaline Earth Metals

• Alkaline Earth metals are very reactive but less
  so than alkali metals

• Alkaline metals harder, more dense than, and melt
  at higher temperatures that alkali metals.

• Alkaline earth metals possess higher ionization
  energies than alkali
• metals

• Some Alkaline metals react directly with water

• Beryllium and magnesium do not react with water,
  however,
• Mg will react with steam.

Mg(s) H2O(g) ? 2MgO(s) H2(g)

• Calcium, Strontium, and barium react directly
  with water

Ca(s) H2O(g) ? 2CaOH(s) H2(g)
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Transitional Elements Comparing 1A and 1B
Elements
K1s22s22p63s23p64s1
Note that both elements have 4s1 valence electrons
Cu1s22s22p63s23p64s13d10
Because the d electrons partially shield the 4s
electron in Cu and because there is a greater
nuclear charge, the 4s electron experiences a
larger effective nuclear charge than its
counterpart in potassium
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Group Trends Selected Nonmetals

• Hydrogen is a nonmetal and is diatomic in nature

• Hydrogen possess no electron shield and therefore
  possess a higher
• ionization energy than other iA elements (I1
  1312 kJ/mol )

• Hydrogen generally reacts with nonmetals to
  produce molecular
• compounds

• Hydrogen reacts with active metals to from solid
  metal hydrides

Mg(s) H2(g) ? 2NaH
Ca(s) H2(g) ? CaH2
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Group Trends Selected Nonmetals

• Oxygen is a colorless diatomic gas. All the
  other VIA elements
• are solid

• Both oxygen and sulfur exist as allotropes
  (different forms of the
• same element)

O2(g) ?O3(g) ?H 264.6 kJ

• Oxygen and Sulfur to a lesser degree, possess
  the ability to attract electrons. Tends to react
  with metals to produce a metal oxide. Also forms
  nonmetal oxides

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Group Trends Selected Nonmetals

• Halogens are generally known as salt formers

• Halogens exist as diatomic molecules

• Melting points of Halogens increase with
  increasing atomic number

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THE END