Simplify the following text for a Grade 6 native English-speaking person.
Original: Molar mass , symbol M , is a physical property characteristic of a given substance ( chemical element or chemical compound ) , namely its mass per amount of substance .
Simplified: The mass number of an element is equal to the molar mass of the element . The molar mass of a chemical compound is the amount that has 6.022 x 1023 molecules .