The Periodic Law

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Chapter 5

• The Periodic Law

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Section 5-1

• History of the Periodic Table

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Stanislao Cannizzaro13 Jul 1826 10 May 1910
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Cannizzaro

• Was the first scientist to accurately measure
  atomic masses.
• This was incredibly important for the work that
  Dmitri Mendeleev was going to do.

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Dmitri Mendeleev8 Feb 1834 2 Feb 1907
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Dmitri Mendeleev

• Arranged the elements on cards in order of
  increasing atomic mass
• Found columns of elements with similar properties
• There were gaps in his columns

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Basic Version of Mendeleevs Periodic Table
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The gaps

• Hypothesized the gaps were undiscovered elements.
• Predicted the props of these elements.
• Predicted them well.

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Mendeleevs Mistake

• There were irregularities when arranged according
  to atomic weight.

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Henry Mosely23 Nov 1887 10 Aug 1915
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Henry Mosely

• Discovered a unique charge on the nucleus of the
  atom.
• Arranged the elements according to increasing
  atomic number
• When he did this, the irregularities disappeared.

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Periodic Law

• The properties of elements tend to change with
  atomic number gradually, in a periodic way.

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John Strutt 12 Nov 1842 30 Jun 1919William
Ramsay2 Oct 1852 23 Jul 1916
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Strutt Ramsay

• In 1894, they discovered argon.
• Nobody noticed it before because it is completely
  unreactive.
• In 1868, helium had been discovered as part of
  the sun and in 1895, Ramsay showed its existence
  on earth.
• In 1898, Ramsay discovered krypton and xenon.
  Friedrich Ernst Dorn discovered radon in 1900.

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Lanthanides

• Discovered in the early 1900s.
• They are found in the f block
• They are shiny and act like the alkaline earth
  metals.

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Actinides

• All of these elements are radioactive.
• They are found in the f block

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Alkali Metals

• Group 1
• These elements are soft and can be cut with a
  knife.
• They are highly reactive. The will react with
  both air and water.
• They form alkaline/basic solutions (the opposite
  of acidic solutions).
• Their electron configurations all end s1.

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Sodium
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Alkaline Earth Metals

• Group 2 on the periodic table.
• These elements are harder and denser than the
  alkali metals.
• They are also reactive, but less so than the
  alkali metals.
• They will also form alkaline/basic solutions.
• Their electron configurations all end s2.

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Magnesium
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Hydrogen

• This element doesnt belong with any group.
• Its electron configuration is 1s1.

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Helium

• Even though its electron configuration ends s2,
  it isnt an alkaline earth metal. It is a noble
  gas because its highest energy level orbitals are
  full.

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Transition metals

• AKA transition elements
• AKA d block elements
• These elements are what we typically picture as
  common metals.
• Their d orbitals are being filled.

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Transition metals contd

• They are shiny and good conductors of
  electricity.
• They are less reactive than the other metals.
• Some like gold are highly unreactive.

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Chromium metal
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Main Group Elements

• Properties of these elements vary greatly because
  they include metals, nonmetals, metalloids, and
  noble gases.
• They include the elements of the s and p blocks.
• Sometimes they are called the representative
  elements because metals, nonmetals, metalloids,
  and noble gases are all represented

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Halogens

• These are the most reactive nonmetals.
• They have 7 electrons in the outermost energy
  level and their electron configurations all end
  in s2p5.
• They will react with metals to form salts.

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Noble Gases

• Group 18
• No stable compounds for He, Ne, or Ar
• Very low reactivity for the rest
• Full s p orbitals (s2p6) in the higest energy
  level
• This is very stable - they have no need to react
  with anything else.

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Noble Gases contd

• Most other atoms gain/lose e- to achieve this e-
  configuration
• Ne Ar are used in signs
• He - Low density - Air ships weather balloons

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Noble Gases Contd

• Rn - Radioactive
• Found in homes - Linked to Lung CA
• Once you test for it, you must disclose the
  results to potential buyers

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5 3 Electron Configuration and Periodic
Properties
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Atomic Radius

• As you move down a group it increases
• The outermost e- are being added to higher energy
  levels (further from the nucleus.

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Atomic Radius

• As you move across a period, it decreases
• Even though e- are being added, they are added to
  the same energy level (same distance from the
  nucleus).

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Atomic Radius

• The charge on the nucleus increases as you move
  across the period and so it has a tighter hold
  on the e- being added.

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Shielding Effect

• The reduction of the attractive force between a
  nucleus and its outer electrons due to the
  blocking effect of inner electrons.

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Ionization Energy

• The amount of energy needed to remove an electron
  from an atom

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Ion

• An atom that has gained or lost an e-
• If it has gained an e-, it will be _____.
• If it has lost an e-, it will be _____.

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Ionization Energy

• As you go down a group, it decreases
• Shielding effect and electrons are being added to
  higher energy levels.

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Ionization Energy

• As you move across a period, it increases
• The charge on the nucleus increases as you move
  across the period and so it has a tighter hold
  on the e- being added.

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Electron Affinity

• Measures the tendency of an atom to attract
  electron
• The energy change that occurs when an electron is
  acquired by a neutral atom.
• Metals tend to have positive energy changes, they
  do not have a tendency to attract electrons
• Non-metals tend to have negative energy changes,
  they have a strong tendency to attract electrons

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EA

• As you move down a group, electrons add with
  greater difficulty (values become more positive)
• Shielding Effect and electrons are being added to
  higher energy levels.
• There are exceptions

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EA

• Electrons add more easily as you move across the
  periodic table.(values become more neg)
• The charge on the nucleus increases as you move
  across the period and so it has a tighter hold
  on the e- being added.

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Electronegativity

• Tendency for an atom to attract e- to itself when
  combined with another atom.
• F is the most EN
• EN decreases as you move down a group
• EN increases as you move across a period

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Electronegativity

• Based on the Pauling Scale.
• Linus Pauling
• 28 Feb 1901
• 19 Aug 1994

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