AQA Chemistry Unit 3 (C3) - The Periodic Table and Its Development, Reactivity Groups, Acids & Alkalis

Notes on the early periodic table, the modern periodic table, alkali metals, transition metals, halogens, development of acid & alkali theories and acid strength.

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Triple Chemistry
The Periodic Table and Its Development
The Early Periodic Table
One of the first attempts at making a proper table of elements was by Manchester physicist
John Dalton, who arranged the elements in order of mass by testing their reactions. A man
called John Newland then expanded on Dalton's ideas and produced a table based on the
Law of Octaves, which stated that every eighth element had similar properties.
Newland was so determined to get his table right that he made some fundamental mistakes
­ in some cases he repeated elements. He didn't take into account elements that hadn't
been found yet and as a result his ideas weren't accepted.
A few more attempts were made at arranging the elements, most notably by French
chemist Alexandre-Emile Beguyer de Chancourtrois, who produced a very good diagram
of the table. Unfortunately his diagram was never published along with his work, so his ideas
were never accepted. In the late 1860's, the Russian scientist Dimitri Mendeleev created
the prototype of the table that is used and recognized worldwide today. Mendeleev still
used Dalton's idea of arranging elements in atomic mass, but also left gaps for undiscovered
elements. He arranged them into further groups based on size and reactivity, and is now
considered the father of the modern periodic table.
The Modern Periodic Table
When protons and neutrons were discovered in the 20th century, the periodic table was
arranged in order of atomic (proton) numbers. This new table was based around
Mendeleev's ideas, with the elements in the same group (vertical) having the same number
of electrons in its outer shell, and elements in the same period (horizontal) having the
same number of occupied energy levels.
Reactivity Groups
Alkali Metals
The elements in group 1 in the periodic table are known as the alkali metals. These
elements get more reactive as you go down the group, as well as having lower melting
and boiling points. This is because alkali metals need to lose an electron to gain a full outer
shell, and the further down the group you get the easier it is for the electron to be lost and

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All of the alkali metals are extremely
reactive, too, and have to be stored in oil otherwise they will react with oxygen in the air.
Additionally, all alkali metals have a low density. Lithium (Li), potassium (K) and sodium (Na)
have such a low density they can float on water ­ they are less dense than water. They form
ionic compounds with non-metals in which the metal ion carries a charge of +1 (as it is
losing an electron).…read more

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Additionally, these ions form different coloured compounds.
Because of the different colours present in transition metal ions, lots of metal compounds
are very colourful. This is why gemstones are coloured, among many other metal
compounds.
One final point about transition metals is that they make good catalysts. Some examples
include:
Manganese oxide used as a catalyst for the decomposition of hydrogen peroxide
Iron used as the catalyst in the Haber process, used for creating ammonia.…read more

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For example:
Chlorine + Sodium Bromide -> Sodium Chloride + Bromine
Cl2 + 2NaBr -> 2NaCl + Br2
Acids & Alkalis
Development of Theories
There have been a few different theories about acids and alkalis throughout the ages. One
Spanish chemist called Arrhenius said that acids release a hydrogen (H+) ion in water. This is
basically a hydrated proton ­ a hydrogen atom has one proton and one electron. If it loses
its electron, it is simply a proton.…read more

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