1.8 - Periodicity

• periodicity

  regularly repeating pattern of atomic, physical and chemical properties with increasing atomic number
• arrangement of modern periodic table

  increasing order of atomic number

  periods: rows; elements in the same periods have the same number of shells

  groups: columns; elements in the same group have the same number of outer electrons
• what does melting point depend on

  structure of element

  type of bonding between atoms
• trends in melting points in the periodic table

  groups 1 to 3: melting point increases as you go across them

  group 4: lower melting point but still high

  groups 5 to 8: low melting point
• melting point of metals

  form metallic bonds so high melting point

  the more electrons each atom contributes to shared delocalised electrons the stronger the bond so that's why group 3 has a higher melting point than group 1
• group 4 bonding

  form giant covalent structures so strong intermolecular forces of attraction so high melting points
• group 5 to 8

  form simple molecules so have weak intermolecular forces of attraction so have a low melting point
• general trend in first ionisation energies across a period

  first ionisation energies increase from left to right because number of protons increases so a stronger nuclear charge so atomic radii decreases and electrons are more attracted to the nucleus
• shielding across a period

  elements have the same number of shells only different numbers of outer electrons which don't shield each other so shielding hardly changes across a period
• drop in ionisation energies between groups 2 and 3

  in group 3 the outer electron is in the p orbital and group 2 it's in the s orbital

  p orbital has a higher energy level so is further away from the nucleus and also has more shielding which overrides effect of increased nuclear charge so ionisation energy drops
• drop in ionisation energies between groups 5 and 6

  shielding is identical and electron is removed from the same orbital

  but group 5 elements don't have paired electrons and group 6 elements do - repulsion is greater between paired electrons so they are easier to remove
• ionisation energies for noble gases

  have the highest ionisation energies because they have a full outer shell so are stable
• huge drop in ionisation energy graph meaning

  new shell: electrons get further from the nucleus so are less attracted to it
• ionisation energies down a group

  decreases as you go down the group because number of shells increases so atomic radius increases so outer electron gets further away from the nucleus so is less attracted to it

  inner shells also shield outer electron from attraction of the nucleus
• what determines atomic radii

  size of positive nuclear charge

  distance of outermost electron from the nucleus
• atomic radii across a period

  decreases across a period because number of protons increases so positive charge increases so electrons are pulled closer to the nucleus
• atomic radii down a group

  increases due to more shells so more shielding so electron are less attracted to the nucleus so are further away from it
• what happens to atomic radius is atom gains electrons

  increases as electrons repel each other so want to put distance between each other
• what happens to atomic radius if atom loses electrons

  decreases as there will be no repulsion so no need to put distance between electrons
• types of atomic radii

  covalent

  ionic

  metallic