The Periodic Table

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Alexandre-Émile Béguyer de Chancourtois

Created the Telluric Spiral:

  • Published in 1862
  • Every turn of the cylinder had a new element directly below it-mass increased by 16.  
  • Elements directly above and below each other had identical properties
  • The paper was hard to understand
  • He did not include a diagram
  • The idea was not accepted.

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John Newlands

Invented the Law of Octaves:

  • Newlands said that properties were repeated every eighth element.
  • Was named the law of octaves because identical patterns occured every eighth element (like in musical octaves)
  • Was not accepted because he included a metal (iron) and non-metals in the same group.
  • Would not have worked with the noble gases because then when lithium was Element 1 Neon would have Element 8, not Sodium.
  • Did not have gaps for new elements.

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Dmitri Mendeleev

Invented what can be considered the first modern periodic table:

  • Organised his table by atomic mass
  • Included gaps for undiscovered elements, such as gallium
  • The discovery of Gallium lent credence to Mendeleev's table

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Noble Gases

Noble gases are in group 0 of the table, on the far right.  They consist of:

  • Helium (2)
  • Neon (10)
  • Argon (18)
  • Krypton (36)
  • Xenon (54)
  • Radon (86)
  • Oganesson (118)

They are extremely unreactive as they contain the maximum amount of electrons in their outer energy levels-8, with 2 for helium.

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Alkali Metals

Alkali Metals are some of the most reactive metals and are found in group 1.  They consist of:

  • Lithium (3)
  • Sodium (11)
  • Potassium (19)
  • Rubidium (37)
  • Caesium (55)
  • Francium (87)

As you go down the table they grow more reactive.  This is because a the lone electron on the outer shell is further away it requires less energy to escape the atom.

Alkali metals typically react with water and oxygen.  When they react with water they produce hydrogen and a metal hydroxide.

In addition, electron shielding occurs.  This means that the electrons near the middle repulse the ones on the edge, causing it to be more easily lost.  

Lastly, all Group 1 metals have one electron on their outer shell.  They therefore make ions with a +1 charge such as Li+.

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Transition Metals

Transition Metals have no group.  They all have 2 electrons on their outer energy level and:

  • are shiny
  • are hard and relatively unreactive
  • have high densities
  • Iron, nickel and copper are magnetic, the rest are not.
  • conduct heat and electricity well.
  • have high melting and boiling points.
  • have colourful compounds. 

As such they are used to colour gemstones, in alloys (like iron and carbon in steel) and as catalysts.

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Halogens

Halogens are reactive gases which are missing one electron on their outer energy level (7 electrons instead of 8).  They are:

  • Fluorine (9)
  • Chlorine (17)
  • Bromine (35)
  • Iodine (53)
  • Astatine (85)
  • Tennessine (117)

The most reactive halogen is flourine.  Electron shielding and distance from the nucleus means that the later elements cannot attract electrons as easily.

All halogens are diatomic, such as F(2).

More reactive halogens, such as fluorine, can displace less reactive ones, such as chlorine, in halogen displacement:

2NaCl+F(2)->2NaF+Cl(2).

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