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WATER…read more

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Periodic Table History
Early 1800s
· there were only two ways to categorize
elements: physical and chemical properties
& relative atomic mass
· nothing was known about atomic structure,
protons or electron so there was no such
thing as atomic number
· so the known elements were arranged in
order of atomic mass
· when this was done a periodic pattern was
noticed in the properties of the elements
Newland's Law of Octaves
· he gave the first food try at arranging the elements in 1864
· he noticed that every eighth element had similar properties so he
listed some of the known elements in rows of seven
· these sets of eights were Newlands Octaves but the pattern broke
down on the third row as the transition metals messed it up
· he left no gaps so his worked was ignored but he was quite close
· his work was criticized because:
· groups contained elements that didn't have similar properties
· metals and non metals were mixed up
· gaps weren't left for elements that hadn't been discovered yet…read more

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Periodic Table History
Dmitri Mendeleev Table of the Elements
· Russia1869, he arranged 50 known element
· he put the elements in order of atomic mass but left gaps to keep elements with similar
properties in the same vertical group
· left very big spaces in the first two rows before the transition metals came in on the third row
· the gaps were really clever because they predicted the properties of so far undiscovered
elements, when they were found and fitted the pattern his table was more convincing
Its Importance
· there wasn't much evidence to support
that the elements fit together in this way
· after newly discovered elements fitted into
the gaps, this was convincing evidence
· once there was more evidence, many
more scientists realized that the periodic
table could be a useful tool for predicting
properties of elements
· in the late 19th century, protons, neutrons
and electrons were discovered, the periodic
table matches up very well to the structure
of the atom
· it is now accepted as a very important
and useful summary of atomic structure…read more

Slide 5

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The Periodic Table
It Is Based On Electronic Structure
· it's a table of all known elements and they
are in order of ascending atomic number
· it is laid out so that the elements form
groups horizontally and periods vertically
· the group the element belongs to is the
same number of electrons it has in its outer
shell and the period the element belongs to
is the same number of shells it has
· maximum number of electrons that can
occupy each shell is given by 2xn², n is the
number of the shell
· positive charge of the nucleus attracts electrons and holds them in place,
the further from the nucleus they are the less the attraction
· attraction of the nucleus is even less when there are a lot of inner electrons,
they get in the way of the charge reducing the attraction, this is shielding
· increased distance and shielding means that an electron in an outer shell is
more easily lost because it has less attraction from the nucleus holding it in
place, so Group 1 metals get more reactive as you go down the group
· increased distance and shielding also means that the outer shell is less
likely to gain an electron as there's less attraction from the nucleus pulling
electrons in, so Group 7 elements get less reactive going down the group…read more

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Group 1 - Alkali Metals
Silvery solids, their hydroxides · they are very reactive, have to
dissolve in water to give an stored in oil and handled with
alkaline solution. forceps as they burn the skin
As you go down Group 1 the alkali · they all have one outer
metals become: electron, making them very
· bigger atoms, there's one extra reactive and gives them all
full shell of electron for each row similar properties
you go down · they form 1+ ions, as they are
· more reactive, outer electron is keen to lose their one outer
more easily lost as it's further from electron
the nucleus · they always form ionic
· higher density, atoms have compounds, so keen to lose
more mass their outer electron they won't
· lower melting point consider sharing electrons
· lower boiling point
Reaction with water produces hydrogen gas
· when put in water they react very vigorously
· move around the surface fizzing furiously, below potassium it gets hot enough to ignite
· produce hydrogen, a lighted splint will indicate it by causing a squeaky pop
· they form hydroxide in solution, aqueous OH- ions
· solution becomes alkaline which changes the colour of the pH indicator to purple
· sodium + water sodium hydroxide + hydrogen…read more

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