Mendeleev arranged the elements known at the time in
order of relative atomic mass, but he did some other things that made
his table much more successful. He realised that the physical and chemical
properties of elements were related to their atomic mass in a 'periodic' way,
and arranged them so that groups of elements with similar properties fell into
vertical columns in his table.
English chemist John Newlands also attempted to classify
the known elements of his day based on their atomic weight. Like de
Chancourtois, he noticed a repeating pattern—every eighth element had similar
properties. Newlands called this the Law of Octaves. Newlands noted that many
pairs of similar elements existed which differed by some multiple of eight in
mass number, and was the first person to assign them an atomic number. However,
when his law of octaves was printed in Chemistry News, likening this
periodicity of eights to the musical scale, it was ridiculed by some of his
contemporaries. His lecture to the Chemistry Society on 1 March 1866 was not
published, the Society defending their decision as they said such 'theoretical'
topics might be controversial. The importance of his analysis was only
recognised by the Chemistry Society with a Gold Medal some five years after
they recognised Mendeleev.
Why the periodic table is called a
periodic table?
It's because the elements are arranged in 'periods', i.e., repeating
sets. In the chemical elements the period is the number of outermost
electrons in a shell, or covalence.
What was wrong with the early periodic
tables?
The early periodic tables did not have a proper order for
all the elements and the theories they gave was not suitable for all elements.
How did Mendeleev solve some of the
problems found in Newland’s table?
Newlands’ periodic table was arranged based on laws of
octaves in which every eight element had similar properties. According to Mendeleev‘s
periodic table the elements were arranged in rows and columns using the
relative atomic mass. Secondly, Newlands periodic table was only for the first
20 elements whereas Mendeleev’s periodic table had spaces for elements which
were yet to be discovered (as there were only about 60 elements that time).
How many electrons do elements in group 1
have in their outer shell?
The modern periodic table is arranged based on the atomic
number whose roots were from Mendeleev’s periodic table
How many electrons do elements in group 1
have in their outer shell?
Group 1 has 1 electron in it's outer shell
What is group 1 called?
Alkali Group
Properties of group 1 metals
·
Group 1 elements are known for being some of the most
reactive metals. This is due in part to their larger atomic radii and low
ionization energies.
·
They tend to donate their electrons in reactions and
often have an oxidation state of +1.
·
These metals are characterized as being extremely
soft and silvery in colour.
·
They also have low boiling and melting points and are
less dense than most elements.
·
Li, Na, and K have the ability to float on water
because of their low density.
Trends seen in group 1
·
Melting and boiling points
The alkali metals all have low melting points and
boiling points compared to other metals. The melting points and boiling points
decrease as you go down the group.
· Reactivity
As you go down the group, the metals become more
reactive. Lithium (at the top) is the least reactive, while francium (which is
at the bottom) is the most reactive.
·
Reactions
Group 1 metals react with non-metals to form ionic
compounds. In these reactions, the metal atom loses its outer electron and
becomes a metal ion with a charge of +1. The ionic compounds produced are white
solids which form colorless solutions when they dissolve.
What is group 7 called?
Halogens
Properties of group 7
·
They are non-metals
·
They have low melting and low boiling points
·
They are brittle when solid
·
They are poor conductors of heat and electricity
·
They have coloured vapours
·
Their molecules are diatomic (each contain two atoms)
- eg chlorine, Cl2
Trends in group 7
·
The melting points and boiling points then increase
as you go down the group.
·
The halogens become darker as you go down the group
·
The halogens become less reactive as you more down
the group. Fluorine (at the top of the group) is the most reactive, while
astatine (at the bottom) is the least reactive.
·
Halogens react with metals to form ionic compounds.
In these reactions, the halogen atoms each gain one electron to form ions with
a charge of –1.
·
The most reactive halogen displaces all the other
halogens from solutions of their salts, while the least reactive halogen is
always displaced. It works just the same whether you use a sodium salt or a
potassium salt.
Where
are the transition metals on the periodic table?
The elements in
the centre of the periodic table - between groups 2 and 3 - are called the
transition elements. They are all metals. They include most of the
commonly-used metals, such as iron, copper, silver and gold.
Properties
of transition metals
·
Most transition metals form colored compounds.
· Many transition elements form ions with different charges. For example,
iron forms iron(II) ions, Fe2+, and iron(III) ions, Fe3+. This means that iron
oxide can exist in two forms, iron(II) oxide, FeO, and iron(III) oxide, Fe2O3.
· Many transition metals act as catalysts in
useful processes. For example, iron is the catalyst used catalyst in the Haber
process when Making ammonia:
hydrogen + nitrogen ->ammonia
3H2(g) + N2(g) -> 2NH3(g)
Differences
between group 1 metals and transition metals.
Properties
|
Group 1 elements
|
Transition elements
|
Melting points
|
Low
|
High (except mercury, which is liquid at room temperature)
|
Reactivity
|
High (react vigorously with water or oxygen)
|
Low (do not react so vigorously with water or oxygen)
|
Strength
|
Soft or liquid so cannot withstand force
|
Strong and hard
|
Density
|
Low
|
High
|
Compounds
|
White or colorless
|
Colored
|
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