The periodic table is most likely the
key tool for chemists. It organizes the elements, but
it also gives a wealth of information.
Key sections of the periodic table
The periodic table is organized in columns, called groups or
families, and rows, called periods. There are several groups or
periods that have specific names.
Important Regions of the Periodic Table:
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Metals |
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Metalloids |
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1. Alkali Metals
2. Alkaline Earth Metals
3. Transition Metals
4. Halogens
5. Nobel Gases
6. Lanthanides
7. Actidines
8 tall columns = main groups or representative
elements
Periodicity
As you move across or down the periodic table, subatomic particles
are added. This increases the mass of the elements both across and
down the periodic table.
Moving across the periodic table, protons are
added to the nucleus while electrons are added to the valence
shell. This increase in both the number of positive charges and
negative charges increases the attraction between the two.
Therefore, when moving across the periodic table, the radius
decreases. When moving down the periodic table, protons are again
added. But this time, the electrons are added in a completely new
valence shell. This new valence shell is shielded from the pull of
the protons by all the inner valence shells. Therefore, as you move
down the periodic table, atomic radius increases.
Electron affinity (the ease with which an
electron is added), electronegativity (pull an electron has on
electrons it shares in a bond) and ionization energy (difficulty in
removing the outermost electron) are all related to the radius. As
radius decreases across the periodic table, all of these properties
increase as the electrons are closer to the pull of the protons. As
radius increases down a group, these properties decrease as the
electrons are farther from the nucleus.
Ionic Radii
The formation of a cation is due to the loss of electrons. A cation
has more protons than electrons and therefore the protons have a
large pull on each electron. The radius decreases. An anion is
formed from the gain of electrons. Anions have a greater number of
electrons than protons. Therefore, the pull of the protons on each
electron is lower. The radius of an anion is greater than the
parent atom.
