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Periodic Table of Elements
4.1
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Dmitri Menveleev
In the last century, a scientist named Dmitri
Mendeleev looked for ways to organize the
current knowledge about newly discovered
elements and their atoms.
He invented a periodic table – an organized
arrangement of elements that explained
and predicted physical and chemical
properties.
Mendeleev’s table was key to understanding
elements and discovering new elements
and compounds.
Initially, Mendeleev organized elements
based on their atomic mass (average
weight of the atoms in the element).
He found that this did not always work.
So he decided to group elements based on
their atomic number (the number of
protons in the nucleus) instead.
Using the periodic table, Mendeleev was
able to actually predict the existance of
certain elements even before they were
discovered!
Ex. Gallium was predicted in 1871 and not
actually discovered until 1875.
Mendeleev’s decision to use the atomic
number rather than atomic mass proved
to be a good one. When subatomic
particles (protons, neutrons, and
electrons) were later discovered, it
became clear that the atomic number
(number of protons in the nucleus) held
the key to the identity of an element.
Groups of Elements
The periodic table groups elements with
similar properties. You can quickly
identify an element as a metal if it is on
the left or in the centre of the table.
Non-metals are generally found on the
right side.
Chemical Groups
The set of elements in the same column in
the table is called a chemical group
(having similar chemical and physical
properties).
These properties, however, vary from
element to element in a column.
Periods
The horizontal rows of elements are
called periods. The first period contains
two elements: hydrogen and helium.
As you go from left to right within a row,
the atomic number increases and the
elements gradually change from metallic
(lithium) to non-metallic (flourine), and
then finally to noble gases (neon) at the
far right.
Today, the modern periodic law states:
If the elements are arranged according to
their atomic number, a pattern can be
seen in which similar properties occur
regularly.
Hand out tables and colour groups to
match the table at the back of the book.
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1
Assignment
Refer to your periodic table as the class
reads pages 110-113 in the text.
Use a colour code and colour your in the
following sections on your periodic
table:
1.
2.
3.
4.
5.
6.
Noble gases
Alkali Metals
Halogens
Group of One
Metalloids
Metals
Group of One
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Hydrogen is a unique element (yellow).
It’s most common isotope has only a single
proton and no neutron in its nucleus.
Hydrogen doesn’t have much in common with
the alkali metals. It’s a colourless, odourless,
tasteless, highly flammable gas.
Almost all of Earth’s hydrogen exists in
combination with other elements. Its
reactivity is too great for it to exist in the
atmosphere as a free element.
Alkali Metals
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Occupy the far left column of the
periodic table (green).
Extremely reactive.
Found in nature only as compounds, and
are found everywhere on Earth.
Most common are sodium compounds,
which occur in plants, animals, soil and
sea water.
Lithium, sodium, potassuim, etc…shiny,
silvery.
Metalloids
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Elements that possess both metallic and
non-metallic properties. Found on both
sides of the zigzag line that divides the
metals from the non-metals.
Ex. silicon, boron, germanium, arsenic,
selenium, antimony, tellurium, polonium,
and astatine.
Halogens
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Occupy the 17th column of the periodic
table (fluorine, chlorine, bromine…)
Most reactive non-metals.
Because of their reactivity, they almost
always appear naturally as compounds,
not as elements.
Most common halogen compounds are
chlorine compounds found in living
things, ocean water and rocks.
Noble Gases
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Occupy the far right column of the
periodic table (blue).
All gases at room temperature, the
noble gases are often called inert gases
because they are so unreactive, almost
never forming chemical compounds with
other elements.
Argon makes up 1% of every breath you
inhale.
Very useful elements. Ex.: neon, helium