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The periodic table
Chemists arranged elements in periodic table, helps make sense of elements and their compounds,
how they will predict etc.
ProtonsElements arranged in Proton number (atomic as well), this is the number of positive
protons in each atom. It's written under each element in the table.
In periodic table, each element shown by its symbol.
Putting them in order shows repetition in properties
Development of the periodic table.
18th century new elements discovered, attempts made to put them in order. Masses could not be
measured so compared against the mass of hydrogen (lightest), called relative atomic mass.
1817 Johann Dobereiner `law of triads'. Realised relative atomic mass of middle element in a
group of 3 elements (possessing similar properties), was close to average of the other two
John Newlands arranged known elements in order of their atomic mass, `law of octaves' every
8th element had similar properties. Didn't work for all known elements, dismissed by scientific
Dmitri Mendeleev put known elements in order of relative atomic mass, left gaps for the
undiscovered and predicted what their properties might be.
Data of the table
The periodic table provides us with a great deal of information, e.g. name, symbol, the proton
number below and above the relative atomic mass.
We can use this to compare e.g. the relative atomic mass of magnesium is 24, twice a carbon atoms
atomic mass (12).
Rows and columns
Divided in horizontal rows and vertical rows.
Metals and nonmetals elements on the left are metals, right non metals, dividing line shown.
Groups=columnscolumn, similar properties called a group, has group number shown on top of
Because of the patterns in the way elements are arranged on the periodic table, it can be used to
predict their properties and interpret data.
Other pages in this set
Here's a taster:
Melting points of some group 1 elements
Element Symbol of element Melting point/°C
Lithium Li 181
Sodium Na 98
Potassium K 63
Rubidium Rb ?
Caesium Cs 29
Melting point shows a pattern, rubidium between 6329 degrees. And it's possible to predict properties of
elements in the same group.…read more