The Periodic Table

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The Periodic Table
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What is the Periodic Table?
The periodic table is a chart that chemists to
organize elements based on their properties The
properties that are used to organize elements
are -- atomic number -- number of valence
electrons -- energy level of the valence
electrons
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Putting Together the Periodic Table
In the 1800s, many scientists suggested putting
the 55 known elements (at the time) into a chart
based on atomic mass, however, no chart was able
to make sense. . . In the 1860s, a Russian
scientists named Dimitri Mendeleev started
looking at other properties of the elements --
he looked at the reactivity of metals, for
example how certain metals tarnish in air -- he
looked at how certain gases are irritating if you
breath them in Mendeleev made cards listing the
properties of each element and began to organize
his chart
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Mendeleevs Chart
Mendeleev managed to put two important
characteristics of each element on his cards --
atomic mass -- number of bonds each element
formed From his cards, Mendeleev organized a
chart in order of increasing mass -- he also put
his elements in different groups based on the
way they bonded to other elements This turned
into the skeleton of todays periodic table --
Mendeleevs table was so good, he was actually
able to predict the atomic mass of three
undiscovered elements!
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The Modern Table
The modern periodic table came into development
in the early 1900s with the discovery of atomic
number. . . From this, we have the modern table,
where the elements increase from left to right by
atomic number and are placed in columns based on
similar physical properties and bonding patterns
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Metals and Non-Metals
On the modern table, the elements on the left of
the table (except hydrogen) are all metals and
have metallic properties On the right side of the
table, all the elements are non-metals Between
the metals and non-metals is a staircase of
elements called metalloids (semi-metals) --
these elements have some metallic and some
non- metallic properties -- the metalloids are
Boron, Silicon, Germanium, Arsenic, Antimony,
Tellurium, and Astatine
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Image of Metals and Nonmetals on the Periodic
Table
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Reading Squares on the Table
Each element has its own square on the periodic
table which tells you several important things
about the element
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Periods and Groups
The rows on the periodic table are called
periods, and are numbered 1 7 from top to
bottom -- elements increase in atomic number
from left to right in a period -- the elements
in a period have very different chemical
properties, and range from metals to
nonmetals The columns on the period table are
called groups or families, and are numbered 1
18 -- each element in a group has similar
properties -- if you dont use the transition
metals, the groups can be renumbered I VIII,
which will be important later
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The Secret of the Table
The secret of the table is that it allows you to
predict the properties of an element
(specifically, the electrons of an element) based
on the periods and groups. . . For example, lets
draw a Bohr model of carbon (atomic 6) How
many valence electrons does carbon have? In what
group (Roman Numeral) is carbon? In what energy
level are these valence electrons? In what period
is carbon?
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The Secret of the Table
The group (I VIII) of an element tells you how
many valence electrons the element has. . . The
period (1 7) of an element tells you what
energy level those electrons are in. . . THIS
DOES NOT WORK FOR TRANSITION METALS!!! -- if you
need to know the valence electrons of transition
metals, I will tell you. . .
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Why the 2 8 18 Bohr Model Doesnt Work . . .
If we were to draw a Bohr Model for Potassium
(19), using, the 2 8 18 model, we would see
that our model predicts 9 valence electrons in
the 3rd energy level -- in reality, K has 1
valence electron in the 4th level The true method
of predicting energy level for all electrons is
called the diagonal rule, which you will learn in
chemistry. . . Basically, because the transition
metals get in the way, the Bohr Model only works
for elements 1 18. -- we also separate the
Lanthanide and Actinide series for this reason