What are the periodic trends? I need help with them.. Regarding atomic mass, (first) ionization energy, electronegativity and anything else im missing. Specially atomic mass, well as you go down a group and atomic number increases, atomic radius increases, ok this makes sense.. number of protons and electrons increase, the valence electron is screened by all the other electrons and thus ISNT pulled towards the center and you have a larger radius.... But why does it decrease as you go left to right in a period? Ionization energy.... hmm not too sure about this... Electronegativity all I know is flourine is the most electronegative and all the elements near the upper right of the periodic table are more electronegative then the ones near the bottom left.... Anything else?