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AS/A-level Chemistry - Trends of the Periodic Table 

Atomic Radii, Ionisation Energy, Electronegativity, Electron affinity, Shielding 

· AS Chemistry,A-level Chemistry,Periodic table,electronegativity,Atomic radii

These are the basics in AS/A-level Chemistry, these information are very useful in reasonings in later topics! 👨‍🏫

Atomic Radii

  • Definition: The atomic radius of a chemical element is a measure of the size of its atoms, usually the mean or typical distance from the nucleus to the boundary of the surrounding cloud of electrons.
  • Atomic radii decreases across the period. 
  • Due to thee increase in nuclear charge across the period, result in a stronger attraction from the nucleus on the negatively charged electrons.

Electron Shielding

  • Definition: The shielding effect describes the decrease in attraction between an electron and the nucleus in any atom with more than one electron shell. It is also referred to as the screening effect or atomic shielding.

  • Shielding increases down the group, hence increases atomic size.

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Ionisation Energy

  • Definition: The energy required to remove the outer-most valence electron on one mole of gaseous state atom to form one mole of gaseous atom with a plus one charge.
  • The ionization energy increases across a period and decreases down a group.
  • It increases across a period because:
    •    The nuclear charge of the nucleus increases across a period, so the energy required to remove the outer-most valence electron also increases.  
  • Ionisation energy decreases down a group due to electron shielding.
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Electron Affinity

  • Definition:  The atom’s desire to gain an electron in order to become stable.

  • Electron affinity increases across a period and decreases down a group.

  • It increases across a period because of the increased nuclear charge means an increased ability to attract a an electron.

  • As you move down a group, electron shielding also has an effect on this as the nucleus’s charge cannot be felt as strongly on potentially gain-able electrons.

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Electronegativity

  • Definition:  The tendency of an atom to attract electrons in an ionic bond.

  • An atom’s electronegativity is affected by its atomic weight and the distance that its valence electrons are from the nucleus.  

  • The higher the electronegativity number is, the more an element, or compound, attracts electrons towards it.   

  • Electronegativity increases across a period and decreases down a group.

  • As you go across a period, the number of charges on the nucleus increases, due to the added protons and electrons.

  • As you go down a group, more and more energy levels are added, the nucleus’s charge is outweighed and doesn’t attract electrons to itself as strongly as the atoms above it in the periodic table.

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Metallic Character 

  • Definition:  An element’s likeness to metals, in terms of its properties or the tendency of an atom to lose an electron to form a positive ion.
  • The metallic character of an element generally decreases across a period and increases down a group. 

  • It decreases across a period because atoms more readily accept electrons to fill a valence shell than lose them to remove the unfilled shell. 

  • The metallic character increases down a group because electrons become easier to lose as the atomic radius increases, where there is less attraction between the nucleus and the valence electrons because of the increased distance between them.

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Element Classification

  • Metals
    • Goof conductors of electricity and heat
    • Retain Ductility 
    • Malleable 
    • Usually havelow ionisation energy 
  • Non-metals
    • High ionisation energies
    • Located in the upper right of the periodic table
  • Diatomic non-metals
    • Hydrogen, Nitrogen, Oxygen, Fluorine, Bromine and Iodine 
    • Covalent Structure 
  • Metalloiids
    • Retain both metallic and non-metallic characteristics
    • 'Semi-metals'
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Reference:

https://getrevising.co.uk/resources/the_trends_of_the_periodic_table

This is the end of the topic!!

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Drafted by Cherry (Chemistry)

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