Periodicity

[[As you move across a period melting point rises across the metals as there are more delocalised electrons and the size of the positive ions increases so there is a greater attraction between the electrons and positive ions.[[
[[Si has a giant covalent structure (tetrahedral) with strong covalent bonds so mp and bp are very high[[
[[As you move across the non-metals mp and bp decreases because they are simple molecular forces with weak London forces between molecules[[

{{Across a period, atomic radii decreases because nuclear pull increases and the electron shielding stays the same{{
{{Down a group, atomic radii decreases because there is more shielding which is stronger than the increasing nuclear pull{{

}}The first ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions}}
}}Its measured in kilojoules per mole (kJ mol^-1) and under standard conditions: 298k and 101kpa}}
}}The first ionisation energy increases across a period because the nuclear charge increases and shielding stays the same, so the attraction of electrons to the nucleus increases and atomic radius decreases.}}
}}There are 2 exceptions:}}
- }}It decreases between group 2 and 13 because group 13 is in p block and group 2 is in s block and p orbitals have slightly higher energy, are marginally further away from the nucleus and have additional shielding so electrons in p orbitals are easier to remove}}
- }}it decreases between group 15 and 16 because in 15 the electron is removed from a slightly occupied orbital but 16 contains 2 electrons = repulsion}}
}}First ionisation energy decreases down a group because there is more shielding, higher atomic radius and the attraction of electrons to the nucleus decreses.}}