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History of the Periodic Table
· In the early 1800's they put elements in order of atomic mass
because they had no idea about atomic structure or protons and
neutrons existing
· When the elements were arranged in order of atomic mass, a
periodic pattern was noticed in the properties of the elements...
which is why it's called the periodic table…read more

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Newlands
· He arranged the elements in order of atomic mass
· Newlands noticed that every 8th element had similar properties and so
listed someone of the known elements in rows of 7
· These sets of 8's were known as Newlands' Octaves
· However, on the 3rd row, the pattern broke down
· His work was ignored because he didn't leave gaps for yet to be
discovered elements. His work was criticised because:
-his groups contained elements that didn't have similar properties
-he mixed up metals and non-metals
-he didn't leave any gaps for yet to be discovered elements…read more

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Mendeleev
· He arranged the elements in order of atomic mass
· Differently to Newlands, he found that he had to leave gaps in order
to keep elements with similar properties in the same groups
· Leaving gaps helped to predict the properties of undiscovered
elements
· When these elements were found, they did fit the pattern…read more

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The Modern Periodic Table
· When protons, neutrons and electrons were discovered, the periodic table was
arranged in order of atomic number and all elements were put into groups. The
elements are arranged by their electronic structure
· Apart from transition metals, elements in the same group have the same
number of electrons in their outer most shell
· The group number is equal to the number of electrons in their outer shell
· The further from the nucleus the electron is, the less attraction to hold the
electron in place
· When there are a lot of inner electrons (shielding) they get in the way and so the
attraction of the nucleus is less
· Increased distance and shielding means electrons in the outer shell are more
easily lost because there's less attraction from the nucleus holding it in place.
Also, it means atoms are less likely to gain an electron because there's less
attraction from the nucleus pulling the electrons into the atom…read more

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Group 1- The Alkali Metals
· As you go down group 1 the alkali metals:
-become more reactive because the electron in the outer shell is more easily
lost it's further from the nucleus
-have lower melting and boiling points
· The alkali metals have low density (the first 3 are less dense than water)
· Lithium, Sodium, Potassium, Rubidium, Caesium
· They only have 1 electron in their outer shell- very reactive
· They are keen to lose the 1 electron to form a 1+ ion
· They always form ionic bonds, producing white compounds that dissolve in water
to form colourless solutions
· They react very vigorously with water and produce hydrogen gas- to test for this
is if a lighted splint squeaks/pops as the hydrogen ignites…read more

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