1. SYMBOLS

2. *big first letter, second letter must be smaller • *element is used to abbreviate the names of • symbols • Ac Actinium • Ag Silver • Al Aluminum • Am Americium • Ar Argon • As Arsenic • At Astatine • Au Gold • B Boron • Ba Barium • Be Beryllium • BhBohrium • Bi Bismuth • Bk Berkelium • Br Bromine • C Carbon

3. ATOMIC MASS

5. ISOTOPES • Isotopes • Atoms of the same element can have different numbers of neutrons; the different possible versions of each element are called isotopes. For example, the most common isotope of hydrogen has no neutrons at all; there's also a hydrogen isotope called deuterium, with one neutron, and another, tritium, with two neutrons.

6. If you want to refer to a certain isotope, you write it like this: AXZ. Here X is the chemical symbol for the element, Z is the atomic number, and A is the number of neutrons and protons combined, called the mass number. For instance, ordinary hydrogen is written 1H1, deuterium is 2H1, and tritium is 3H1.