Trends in the Periodic Table

the patterns in the periodic table

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Density & Melting and Boiling Points

  • solids have great densities
  • gases have small densities
  • general decrease across a period
  • general increase down the group
  • general increase in melting and boiling points down a group
  • general decrease in melting and boiling points across a period
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Atomic Size / Covalent Radius

  • half the distance between nuclei and bonded atoms
  • general increase down a group because:
    • there is an increase in the number of electron shells
    • the outer electrons are further from the nucleus
  • general decrease across a period:
    • there is an increase in nuclear charge
    • therefore there is an increase in attraction between the nucleus and its outer electrons
    • electrons are held more tightly
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Ionisation Energy

First Ionisation Energy

  • the energy required to remove one electron from an atom of a certain element
  • general increases down a group because:
    • there is an increase in nuclear charge
    • there is a decrease in covalent radii so the electrons are held more tightly
  • general decreases across a period because:
    • there is an increase in electron shells causing a shielding effect
    • electrons held less tightly to nuclei

Second Ionisation Energy

  • the energy required to remove a second electron from a now singularly positive ion of a certain element
  • group 1 elements have a much higher second ionisation energy than their first because:
    • when a second electron is removed, stability is being destroyed
    • full electron shells are much harder to break than partially full ones
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Electronegativity

  • the attraction of an atoms nuclei to its bonding electrons
  • there are no values for the noble gases as they have no bonding electrons
  • general increase across a period because:
    • there is a decrease incovalent radius
    • there is an increase in nuclear charge
    • electrons are held more tightly
  • general decrease down a group because:
    • there is an increase in covalent radius
    • the outer electron shells cause a shielding effect
    • generally the electrons are held looser
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Comments

Shamma

Doesn't the first IE decrease going down a group? 

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