The difference between BAKING Soda and WASHING Soda is one sodium atom and 1 Hydrogen atom. Baking soda is Sodium Bicarbonate (NaHCO3) whereas Washing Soda is Sodium Carbonate (Na2CO3). That molecular structure makes Washing Soda more receptive and allows it to scrub more thoroughly.
Additionally, Baking Soda has a pH of about 8 (slightly alkaline) whereas Washing Soda has a pH of about 11 (so alkaline it’s caustic) which is why you should NEVER bake with washing soda. (Don’t ask how I found out.)