The periodic table is a table that organises
the elements by their atomic number, electronic
configuration and chemical properties.
But even before any table of elements was
formed,
Scientists were observing curious patterns
amongst the known elements.
Over the years, as more and more elements
have been discovered, similarities in the
way elements reacted with different things
were observed.
For example, some gases are completely unreactive
with everything,
while some metals have a vigorous reactions
with water.
Properties like these allowed elements to
be grouped together.
In the 1800s not a lot was known about elements.
Protons, neutrons and electrons weren't even
an idea!
So the only logical way to order elements
was by order of their atomic mass.
In 1817 one of the first patterns amongst
the known elements was observed. Johann Wolfgang
Doberiner noticed he could form groups of
3 with elements exhibiting similar properties,
he termed these groups; Triads.
An example of one of these triads was lithium,
sodium and potassium, the interesting characteristic
of triads, was that when they were placed
in order of their atomic mass; the middle
element always had an atomic mass which was
an average, or very close to an average of
the other 2 elements in the triad.
50 years later came 'Newland's Octaves'
Newland noticed that when the elements are
arranged in order of their atomic weight every
eighth element had similar properties, so
he listed some of the known elements in rows
of seven.
His pattern only worked up to a certain point;
it broke down in the 3rd row, with the transition
metals like Iron, Copper and Zinc, causing
a massive flaw in his theory.
His theory was met with ridicule, but he was
close. The problem with his arrangement was
that he left no gaps.
Not all elements had been discovered yet,
in fact none of the group 0 elements had been
discovered at all, and many of the elements
had been assigned incorrect atomic weights.
He had also not predicted the complex nature
of elements.
In 1867, Dimitri Mendeleev formed the first
table of elements. He anticipated complexities
and missing elements and transformed 'Newland's
Octave' into a plausible arrangement. He
even went as far as to change atomic weights
of known elements so that they would fit into
his arrangement.
His table allowed him to look at the elements,
and from there predict the properties of those
missing elements, and as more and more elements
were discovered his tables when through many
redrafts.
One of the gaps in Mendeleev's table was
found below Aluminum, he predicted the properties
of this mystery element and that it would
have an atomic weight of around 68.
In 1867 Gallium was discovered, the mystery
element.
Mendeleev's predicted properties matched
this new elements property almost exactly,
marking a turning point in the world of chemistry,
and his table started to become widely accepted.
There were still a few problems with Mendeleev's
periodic table.
When Mendeleev began drawing up the periodic
table the Noble Gases hadn't been discovered
yet.
When argon was discovered, it didn't fit
into Mendeleev's table.
It was put into a new group, group 0, and
over the next few years other members of this
group were discovered.
Other problems with the ordering of atomic
weight also caused issues.
These problems have been solved in modern
version of the periodic table we use today
giving us an excellent resource to understand
the elements and all that we and our surroundings
are made of.
