Remember, we can represent electron configurations two ways:

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Remember, we can represent electron
configurations two ways
Written configuration Ne 1s22s22p6
or Box diagram 1s2 2s2 2p6 Ne
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For Neon (Ne), either way is fairly easy. IF,
however, we want to write the configuration for
Lead (Pb) it gets lengthy.
Written configuration Pb 1s22s22p63s23p64s23d
104p65s24d105p66s2
or Box diagram Its quite long, not going to
do it.
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We can avoid writing the inner level electrons by
just writing the name of the last element in the
previous energy level (n-1) and the electron
configuration for the electrons for the final
energy level (n). For Magnesium
Ne3s2 Neon is the last element in the n 2
energy level. Magnesium has 12 electrons so has
two more electrons than Neon which go into the 3s
orbital.
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Energy Levels n 2 (or n-1) n 3
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For Sulfur
Ne3s23p4 Neon is the last element in the n 2
energy level. Sulfur is in the n 3 energy
level, has 16 electrons so has six more electrons
than Neon. Two go into the 3s orbital and 4 go
into the 3p orbital.
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Energy Levels n 2 (or n-1) n 3
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For Gallium
Ar4s23d104p1 Argon is the last element in the
n 3 energy level. Gallium has 31 electrons so
has thirteen more electrons than Argon. Two go
into the 4s orbital and ten go into the 3d
orbital and one goes into the 4p orbital.
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Energy Levels n 3 (or n-1) n 4
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How do you know what order to fill electron
orbitals? The text gives two examples of the
order for filling electron orbitals on page 345.
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6s ? 5p ??? 4d ????? 5s ? 4p ??? 3d ????? 4s ? 3p
??? 3s ? 2p ??? 2s ? 1s ?
One way is a vertical list filling orbitals going
up
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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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A third way that is possibly easier to remember
is the Diagonal Rule. List the orbitals below
on a piece of paper. 1s 2s, 2p 3s, 3p, 3d 4s, 4p,
4d, 4f 5s, 5p, 5d, 5f 6s, 6p, 6d, 6f 7s, 7p, 7d,
7f
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The Diagonal Rule
Electrons fill the orbitals in this order. Draw
the diagonal lines.
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The Diagonal Rule
You only have to remember s, p, d, f
And to line them up 1s 2s, 2p 3s, 3p, 3d 4s, 4p,
4d, 4f
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Valence electrons and core electrons
The most important electrons to chemists are the
ones that attach to each other to form bonds.
These are the electrons in the outermost level
and are called valence electrons. The inner
electrons are not involved in bonding and are
called core electrons.
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Valence electrons appear periodically.
As we build up electrons, the same type of
orbitals occur going from one energy level to
another. The valence electrons are those that
occur in the outer orbitals, the s p orbitals.
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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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• What are the valence electrons for
• Carbon (C)
• 2s22p2
• Sodium (Na)
• 3s1
• Iodine (I)
• 5s25p5

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• END

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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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Reactivity Trends From the Lab

• What did you find going down the first column in
  the periodic table?

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Reactivity Trends

• What about going across a period in the Periodic
  Table?

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• How do the alkali and alkaline earth metals react
  with water?
• With HCl?

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• As you go from top to bottom in a metal family,
  reactivity
• As you go from left to right on the metal side of
  the periodic table, reactivity
• Why?
• Reactivity of a metal is related to the ease of
  losing electrons (ionization energy)

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Nonmetal reactivity

• The trends are exactly opposite to the metals on
  the nonmetal side of the periodic table.
• As you go down a nonmetal family, the reactivity
• As you go from left to right in a nonmetal
  period, reactivity
• Why?
• Reactivity of a nonmetal is based on how strongly
  attracted an added electron is to a neutral atom.

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What about size of atoms?

• As we go down a column in the periodic table?

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Why?
WHY?
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• Why does atomic size decrease from left to right
  in a period but increase as you go down a family?
• Size of an atom depends on the size of the pull
  of the nuclear protons on the electrons
• In the same period, electrons in the same shell
  are pulled by an increasing number of protons

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• As you go down a family, though there are
  increasing number of protons in the nucleus,
• Their pull is diminished by filled inner orbitals
  (repulsion by core electrons)
• As the shell number increases, the distance from
  the nucleus increases and there is less
  attraction of the outer electrons to the nucleus

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Ionization Energy

• What is it?
• The ability to lose or have an electron ripped
  away.

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How does ionization energy change down a column
in the periodic table?
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Explaining the trends in ionization energy
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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.

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Size of Ions

• Which is bigger?
• Br-1 or Cl-1
• Na or Na1
• K1 or Cl-1 or Ar
  (they all have the same number
  of electrons!)