Before you begin, let's see what you need to learn. After writing your answer in your notes, check your answers.

Question	Check Your Answer
If the atomic mass of an atom is 16, and its atomic number is 7, how many neutrons does it have?	Interactive popup. Assistance may be required. Check Your Answer 16 amu – 7 protons = 9 neutrons 1 proton has the same mass as 1 neutron = 1 amu
How are isotopes of the same element different?	Interactive popup. Assistance may be required. Check Your Answer The mass number is different because the number of neutrons is different.
What does H-3 mean?	Interactive popup. Assistance may be required. Check Your Answer This hydrogen isotope has an atomic mass of 3amu or 1 proton and 2 neutrons.
What is a weighted average?	Interactive popup. Assistance may be required. Check Your Answer It is the sum of the percent occurrences of each item in the list.