The History of the Modern Periodic Table

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The History of the Modern Periodic Table
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During the nineteenth century, chemists began to
categorize the elements according to similarities
in their physical and chemical properties. The
end result of these studies was our modern
periodic table.
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Johann Dobereiner
In 1829, he classified some elements into groups
of three, which he called triads.The elements in
a triad had similar chemical properties and
orderly physical properties.
(ex. Cl, Br, I and Ca, Sr, Ba)
Model of triads
1780 - 1849
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John Newlands
In 1863, he suggested that elements be arranged
in octaves because he noticed (after arranging
the elements in order of increasing atomic mass)
that certain properties repeated every 8th
element.
1838 - 1898
Law of Octaves
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John Newlands
His law of octaves failed beyond the element
calcium.
WHY?
Would his law of octaves work today with the
first 20 elements?
1838 - 1898
Law of Octaves
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Dmitri Mendeleev
In 1869 he published a table of the elements
organized by increasing atomic mass.
1834 - 1907
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Lothar Meyer
At the same time, he published his own table of
the elements organized by increasing atomic mass.
1830 - 1895
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Elements known at this time
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• Both Mendeleev and Meyer arranged the elements in
  order of increasing atomic mass.
• Both left vacant spaces where unknown elements
  should fit.

So why is Mendeleev called the father of the
modern periodic table and not Meyer, or both?
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Mendeleev...

• stated that if the atomic weight of an element
  caused it to be placed in the wrong group, then
  the weight must be wrong. (He corrected the
  atomic masses of Be, In, and U)
• was so confident in his table that he used it to
  predict the physical properties of three elements
  that were yet unknown.

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After the discovery of these unknown elements
between 1874 and 1885, and the fact that
Mendeleevs predictions for Ga, Sc, and Ge were
amazingly close to the actual values, his table
was generally accepted.
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However, in spite of Mendeleevs great
achievement, problems arose when new elements
were discovered and more accurate atomic weights
determined. By looking at our modern periodic
table, can you identify what problems might have
caused chemists a headache?
Ar and K
Co and Ni
Te and I
Th and Pa
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Henry Moseley
In 1913, through his work with X-rays, he
determined the actual nuclear charge (atomic
number) of the elements. He rearranged the
elements in order of increasing atomic number.
There is in the atom a fundamental quantity
which increases by regular steps as we pass from
each element to the next. This quantity can only
be the charge on the central positive nucleus.
1887 - 1915
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Henry Moseley
His research was halted when the British
government sent him to serve as a foot soldier in
WWI. He was killed in the fighting in Gallipoli
at the age of 28. Because of this loss, the
British government later restricted its
scientists to noncombatant duties during WWII.
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Glenn T. Seaborg
After co-discovering 10 new elements, in 1944 he
moved 14 elements out of the main body of the
periodic table to their current location below
the Lanthanide series. These became knownas the
Actinide series.
1912 - 1999
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Glenn T. Seaborg
He is the only person to have an element named
after him while still alive.
"This is the greatest honor ever bestowed upon me
- even better, I think, thanwinning the Nobel
Prize."
1912 - 1999
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Periodic Table Geography
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The horizontal rows of the periodic table are
called PERIODS.
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The elements in any group of the periodic table
have similar physical and chemical properties!
The vertical columns of the periodic table are
called GROUPS, or FAMILIES.
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GroupsHeres Where the Periodic Table Gets
Useful!!

• Elements in the same group have similar chemical
  and physical properties!!
• (Mendeleev did that on purpose.)

• Why??
• They have the same number of valence electrons.
• They will form the same kinds of ions.

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Families on the Periodic Table

• Families may be one column, or several columns
  put together.
• Families have names rather than numbers. (Just
  like your family has a common last name.)

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Periodic Law
When elements are arranged in order of increasing
atomic number, there is a periodic pattern in
their physical and chemical properties.
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Classification of Elements
Insert figure 4.6
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B. Blocks

• Main Group Elements
• Transition Metals
• Inner Transition Metals

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A. Metallic Character

• Metals
• Nonmetals
• Metalloids

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Classification of Elements

• Metals left of diagonal line
• 1. Shiny (high luster)
• 2. Malleable
• 3. Ductile
• 4. Conduct Heat and Electricity
• 5. Combine Chemically with nonmetals
• alloys - mixtures of metals
• - copper and zinc make brass
• most found in nature combined with oxygen
• alkali metals very reactive
• noble metals, Cu, Ag, Au, Pt can be found as pure
  elements

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Classification of Elements

• Nonmetals right of diagonal line
• 1. Dull
• 2. Brittle
• 3. Poor Conductors of Heat and Electricity
• 4. Combine with metals and with nonmetals
• O, N, C, and S can be found pure in nature
• F most reactive

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Classification of Elements

• Metalloids on diagonal line except Al
• 1. semiconductors
• 2. some shiny, some not
• 3. Properties between metals and nonmetals
• most common is silicon
• 2nd most abundant on earth, found as silicates
• - chemically bonded oxygen and silicon

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Diatomic Elements
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Hydrogen

• Hydrogen belongs to a family of its own.
• Hydrogen is a diatomic, reactive gas.
• Hydrogen was involved in the explosion of the
  Hindenberg.
• Hydrogen is promising as an alternative fuel
  source for automobiles

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Alkali Metals
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Alkali Metals

• 1st column on the periodic table (Group 1) not
  including hydrogen.
• Very reactive metals, always combined with
  something else in nature (like in salt).
• Soft enough to cut with a butter knife

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Alkaline Earth Metals
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Alkaline Earth Metals

• Second column on the periodic table. (Group 2)
• Reactive metals that are always combined with
  nonmetals in nature.
• Several of these elements are important mineral
  nutrients (such as Mg and Ca

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Transition Metals
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Transition Metals

• Elements in groups 3-12
• Less reactive harder metals
• Includes metals used in jewelry and construction.
• Metals used as metal.

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Boron Family

• Elements in group 13
• Aluminum metal was once rare and expensive, not a
  disposable metal.

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Carbon Family

• Elements in group 14
• Contains elements important to life and
  computers.
• Carbon is the basis for an entire branch of
  chemistry.
• Silicon and Germanium are important
  semiconductors.

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Nitrogen Family

• Elements in group 15
• Nitrogen makes up over ¾ of the atmosphere.
• Nitrogen and phosphorus are both important in
  living things.
• Most of the worlds nitrogen is not available to
  living things.
• The red stuff on the tip of matches is phosphorus.

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Oxygen Family or Chalcogens

• Elements in group 16
• Oxygen is necessary for respiration.
• Many things that stink, contain sulfur (rotten
  eggs, garlic, skunks,etc.)

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Halogens
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Halogens

• Elements in group 17
• Very reactive, volatile, diatomic, nonmetals
• Always found combined with other element in
  nature .
• Used as disinfectants and to strengthen teeth.

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Noble Gases
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The Noble Gases
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The Noble Gases

• Elements in group 18
• VERY unreactive, monatomic gases
• Used in lighted neon signs
• Used in blimps to fix the Hindenberg problem.
• Have a full valence shell.

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The periodic table is the most important tool in
the chemists toolbox!
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B. Chemical Reactivity

• Alkali Metals
• Alkaline Earth Metals
• Transition Metals
• Halogens
• Noble Gases

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Physical State at Room Temperature (20o C)

• Depends on melting point and boiling point
• 11 are Gases
• Noble Gases He, Ne, Ar, Kr, Xe, Rn
• Other Gases H2, N2, O2, F2, Cl2
• 2 are Liquids
• Br2, Hg
• All others Solids
• Metals like Na, Ag, Fe, Au, Pb, K, Ca, Cu, Li,
  Sn, Cr
• Non-metals like B, C, P, S, I2,
• Metalloids like Si, As, Sb, Te

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We will be looking at the following periodic
trends in this chapter
Atomic size, Ionic size, Ionization
energy, Electronegativity.