▁ad s orb ate ▁is ▁minimal . ▁ ▁For ▁chem is or ption , ▁changes ▁in ▁the ▁electronic ▁states ▁may ▁be ▁detect able ▁by ▁suitable ▁physical ▁means . ▁ ▁Typ ical ▁binding ▁energy ▁of ▁phys is or ption ▁is ▁about ▁ 1 0 – 1 0 0 ▁me V . ▁ ▁Chem is or ption ▁usually ▁forms ▁bond ing ▁with ▁energy ▁of ▁ 1 – 1 0   e V . ▁ ▁The ▁elementary ▁step ▁in ▁phys is or ption ▁from ▁a ▁gas ▁phase ▁does ▁not ▁involve ▁an ▁activation ▁energy . ▁ ▁Chem is or ption ▁often ▁involves ▁an ▁activation ▁energy . ▁ ▁For ▁phys is or ption , ▁under ▁appropriate ▁conditions , ▁gas ▁phase ▁mole cules ▁can ▁form ▁mult il ayer ▁ad s or ption . ▁ ▁In ▁chem is or ption , ▁mole cules ▁are ▁ad s or bed ▁on ▁the ▁surface ▁by ▁val ence ▁b onds ▁and ▁only ▁form ▁mon ol ayer ▁ad s or ption . ▁ ▁A ▁direct ▁transition ▁from ▁phys is or ption ▁to ▁chem is or ption ▁has ▁been ▁observed ▁by ▁att aching ▁a ▁CO ▁mole c ule ▁to ▁the ▁tip ▁of ▁an ▁atomic ▁force ▁mic ros cope ▁and ▁meas uring ▁its ▁interaction ▁with ▁a ▁single ▁iron ▁atom . ▁* ▁ ▁See ▁also ▁Ad s or ption ▁Chem is or ption ▁van ▁der ▁Wa als ▁force ▁ ▁References ▁ ▁Category : Sur face ▁science <0x0A> </s> ▁Felix ▁Dar four ▁or ▁Dar fur ▁( c . 1 7 4 0 – 1 8 2 2 ) ▁was