The Diagonal Rule

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The Diagonal Rule
Electrons fill the orbitals in this order
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Valence electrons
Electrons in the s p orbitals determine the
valence electrons
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The other way is a table filling orbitals from
left to right and going down one period at a time
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The Periodic Table

• Some definitions
• Family a vertical column (group)
• These elements have similar properties and
  reactivity
• Period a horizontal row
• This represents the shell or energy level
• Periodicity the pattern of repeating
  properties across a period that was discovered
  by early chemists

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Names of Groups
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• Metals and Nonmetals

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• Metals typically have these characteristics
• are lustrous in appearance
• change shape without breaking
• are excellent conductors of electricity and heat
• Tend to lose electrons to form positive ions
  (cations)

Nonmetals typically do not have these
characteristics. Tend to gain electrons to form
negative ions (anions)
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Metals and Nonmetals

• As you go from top to bottom in a family,
  reactivity increases. The atoms that lose
  electrons more easily are more reactive.
• Cs gt Rb gt K gt Na gt Li

Loses an electron most easily
Least likely to lose an electron
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Metals and Nonmetals

• The alkali metals and the alkaline earth metals
  loose electrons to form positive ions (cations)
• (Alkali metals) Cs gt Rb gt K gt Na gt Li
• (Alkaline earth metals) Ba gt Sr gt Ca gt Ng gt Be

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Metals and Nonmetals

• The energy required to remove an electron
  increases as you go left to right in each period
  of the periodic table.
• Li lt Be lt B lt C lt N lt O lt F lt Ne

Least energy required
Most energy required
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Metals and Nonmetals

• The nonmetals to the right side of the periodic
  table tend to gain electrons to form negative
  ions (anions)

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Ionization Energy
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Ionization Energy

• The energy required to remove an electron from an
  individual atom in the gas phase

Energy required to remove an electron
Period
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Ionization energies generally increase across a
period
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Ionization Energy

• The energy required to remove an electron from an
  individual atom in the gas phase

Group
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Ionization energies generally decrease down a
group
Energy required to remove an electron decreases
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Explaining the trends in ionization energy
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• Metals and Nonmetals

Most reactive
Most reactive
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Why?
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What about size of atoms?

• As we go down a column in the periodic table,
  atom size increases.
• As principle energy levels increase the size of
  the orbitals increase.
• As we go right across each period, atom size
  decreases.
• As the number of protons increase, electrons are
  attracted closer to the nucleus.

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Atomic Size, Ionization Energy and Reactivity are
all related!

• In all atoms a larger size makes it easier to
  take an electron away? lower Ionization energy.
• Since metals react by losing electrons, the
  larger they are, the more reactive they are.
• Since non-metals react by gaining electrons, the
  smaller they are, the more reactive they are.