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The Periodic Table
Chapter 5
section 1 & 2
Patterns and Discovery
Dmitri Mendeleev was the first to
discover that the elements had a
pattern to them and organized them
as such.
 Properties are periodic meaning they
had a repeating pattern

Mendeleev arranged elements by
increasing atomic mass
 By arranging this way, he was able
to predict the properties of elements
that were not discovered yet.

How is that possible?
By looking at the elements that
came before and after
 Ex- you go to school, and there is no
mail in the mailbox. You come
home and there is. Although you
did not see the mailman you can be
reasonable sure that he/she was
there while you were gone. That is
deductive reasoning.

Where did Mendeleev fall
short?



By arranging atoms in order of increasing
atomic mass, some of the elements
seemed out of place
Henry Moseley changed Mendeleev’s
periodic table and put the atoms in order
according to increasing atomic number
(protons)
This fixed the problem. Now all of the
elements fell into place
Periodic Law
For something to be periodic, it
needs to be a regular repeating
pattern, much like the days of the
week
 Periodic Law states that the
chemical and physical properties of
elements are periodic functions of
their atomic numbers.

Blocks on the Table
In each block the symbol, the name
of the element, the atomic number,
and the atomic mass are printed.
 Some periodic tables have even
more information than that

Reading the Periodic Table
Rows are called periods (they go
across the periodic table)
 Each period corresponds to the
number of energy levels the element
has
 Period 2 has elements with 2 energy
levels and so on

Columns

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Columns are called groups or families
(they go down the periodic table)
Each element in the group shares similar
physical and chemical properties
Each element in the group has the same
number of valence electrons (electrons in
the outer shell) which are responsible for
bonding
Alkali Metals
Soft
 Most reactive metals
 Low density
 Give away their electrons the easiest

Alkaline Earth Metals
Not as eager to give away electrons
as the alkali metals
 Reactive but not as much as the
alkali metals

Transition Metals
Not as reactive as alkali or alkaline
earth metals
 Can have different numbers of
valence electrons based on the
specific type of element
 Higher densities and melting points
than alkali or alkaline earth

Rows Within the Transition
Metals

These are at the bottom of the table
Lanthanides – shiny and reactive
 Actinides – radioactive and unstable

Halogens
Non-metals
 React violently to alkali elements
and when they do they form salts
 Never found alone in nature

Noble Gases
Un-reactive
 All are gas at room temperature
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