Her behavior has been reinforced (i.e. strengthened). Reinforcement can be external or internal and can be positive or negative. If a child wants approval from parents or peers, this approval is an external reinforcement, but feeling happy about being approved of is an internal reinforcement.
It remained to define the unit of amount of substance by fixing the corresponding mass of carbon 12; by international agreement, this mass has been fixed at 0.012 kg, and the unit of the quantity amount of substance was given the name mole (symbol mol).
The mole is currently defined as the quantity of entities (elementary particles like atoms or molecules) equal to the number of atoms in 12 grams of carbonâ12. Thus, the current definition of the mole requires that 1000â12 (83â) moles of 12 C has a mass of precisely one kilogram.