Transcript Chapter 4 Section 2 - Garnet Valley School District

Chapter 4
Section 2
Organizing the Elements
I. Patterns in the Elements
A. Mendeleev’s work
1. In 1871, Russian scientist Dmitri
Mendeleev noticed that some elements
had similar physical and chemical
properties.
a. Silver and copper are both shiny metals that
tarnish.
b. Chlorine and fluorine are both gases that
irritate the lungs and form similar compounds.
2. These properties might hold a clue to
a hidden pattern.
3. Mendeleev made 63 cards, one for
each element, listing their properties
and atomic masses.
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4. He noticed that when placed in order
of increasing atomic mass, a pattern
appeared . If an element had similar
properties to the next group , he
assumed that there must be an
undiscovered element and successfully
predicted the missing element.
a. Predicted 3 new elements which
were discovered within the next
16 years.
5. Called his chart the Periodic Table.
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Scandium discovered
in 1879
Gallium Germanium discovered discovered in
in 1875
1886
6. In 1913, British scientist Henry Mosely
discovered a way to measure the number
of protons in an atom (atomic #).
7. By changing from atomic mass to atomic
number, the patterns became more
regular and formed the current version of
the table.
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B. Organization of the Periodic Table
1. Properties of an element can be
predicted from its location on the
periodic table.
2. Periods are horizontal rows on the
table.
a. The properties of the elements change in a
pattern.
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3. Groups are vertical columns on the
Be
table which contain elements with
similar properties.
12
Mg
a. also called families.
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4. Symbols for elements are always an
Ca
uppercase letter first then a lower
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case letter if it has 2. Unnamed
Sr
elements have 3 letters that tell the
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atomic number.
Ba
5. Symbols can be from latin names,
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common names, famous scientists or Ra
places.
6. Reading an Elements Square
Atomic Number
(# of protons)
Chemical Symbol
Element Name
Atomic Mass
(Protons + Neutrons)
26
Fe
Iron
55.847
Atomic Radius in periods and in groups.
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C. How Elements Form in Stars
1. The sun is made up of mostly 1
element, hydrogen.
2. The hydrogen is so hot it is in a phase
of matter called a plasma (gaslike
mixture of free electrons and nuclei of
atoms).
3. The pressure in a star is so high, the
protons are squeezed together and
collide.
4. Nuclear Fusion is when two atomic
nuclei combine and “fuse” together. This
releases huge amounts of energy and
forms a new element.
5. Stars create heavier elements until they
reach a maximum size nucleus.
a. Our star will probably max out at
Oxygen.
b. The largest stars will max out at
Iron (Fe).
6. The only way heavier elements are
created is during massive explosions
called supernovas.
Crab Nebula – first observed in 1045 A.D.
Cosmic Scale Models