periodicity

• periodicity is the repeating pattern of physical trends or chemical properties going across the periods
• elements are classed as being in the s,p or d block according to which orbitals the highest energy electrons are in
• atomic radii decreases from left to right across a period because the increased number of protons create more positive charge attraction for electrons which are in the same shell with similar shielding
• 1st IE increases across a period as there are an increasing number of protons as electrons are being added to the same shell
• there is a small drop in IE between Mg and Al

  Mg has outer electrons in 3s subshell whereas Al starts to fill the 3p subshell

  3p electrons are higher in energy so Al's electron is slightly easier to remove
• small drop between phosphorous and sulfur

  sulfur's outer electron is paired in the 3p orbital, when the second electron is added to the orbital there is a slight repulsion between two negatively charged electrons which makes the second electron easier to remove
• Na, Mg and Al have strong metallic bonding which gets stronger with more electrons in the outer shell being released to the sea of electrons

  lots of energy required to break bonds so high melting and boiling point
• smaller size ion with a greater positive charge also makes the metallic bonding stronger
• Si is a macromolecule

  many strong covalent bonds between atoms require lots of energy to overcome

  high melting and boiling point
• Cl2 S8 and P4 are simple molecules with weak van der waal forces between molecules so little energy is required to overcome the forces
• S8 has a higher mp than P4 because it has more electrons so has stronger van der waal's forces between molecules
• Ar is monoatomic so has weak van der waal forces between atoms and a very low melting point
• melting and boiling points

  macromolecule > metals > molecular gas > monoatomic