the periodic table how the elements are organized
Post on 25-Dec-2015
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John Newlands
Arranged the known elements according to their properties and in order of increasing atomic mass
He placed the elements in a table
Law of Octaves
The pattern discovered by John Newlands
All elements in a given row had similar chemical and physical properties and these properties seemed to repeat every eight elements
Dmitri Mendeleev
1869, produced the first orderly arrangement of elements in the periodic table
Elements are arranged in order of increasing atomic mass
He even predicted elements that had not been discovered yet
Periodic Law
States that when the elements are arranged according to their atomic numbers, elements with similar properties appear at regular intervals
Valence Electrons
Elements in each column of the periodic table have the same number of electrons in their outer energy level (valence electrons)
It is the valence electrons of an atom that participate in chemical reactions with other atoms, so atoms with the some number of valence electrons tend to react in similar ways
Groups
A vertical column on the periodic table Elements in the far left column have 1
valence electron Elements in the far right column have 8
valence electrons
Period
A horizontal row on the periodic table Elements in the same period have the
same number of occupied energy levels
Main Group Elements
In the s and p blocks of the periodic table
The configuration of their valence electrons can be written as ns2
Sometimes called the representative elements because they have a wide range of properties
Alkali Metals- Group 1
Are metals that react with water to make alkaline solutions
Ex.-Potassium reacts vigorously with cold water to form hydrogen gas and the compound potassium hydroxide, KOH
Have a single valence electron, very reactive
When they lose the valence electron they become stable
Alkali Metals, cont.
Stored in oil Never found in nature as pure
substances, but only as compounds (such as NaCl)
Soft metals Good conductors of electricity
Alkali Metals
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Potassium
Alkaline-Earth Metals
Highly reactive, found as compounds rather than pure elements
Slightly less reactive than the alkali metals
Have two valence electrons and must lose both to get a stable electron configuration
Harder and have higher melting points that alkali metals
Halogens-Group 17
The most reactive group of nonmetal elements because of their 7 valence electrons, only need 1 electron for a stable configuration
Often react with alkali metals which only have one valence electron
React with most metals to form salt (Halogen means “salt maker”)
Noble Gases- Group 18
Unreactive, have a full set of valence electrons
Except for helium they all have an outer shell configuration of ns2np6 (n is the period number)
Hydrogen
Most common element in the universe Consists of just one proton and one
electron Behaves unlike any other element Can react with many other elements,
including oxygen
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