| A | B |
|---|
| atom | the smallest particle into which an element can be divided and still be the same substance |
| theory | a unifying explanation for a broad range of hypotheses and observations that have been supported by testing |
| electrons | the negatively charged particles found in all atoms; electrons are involved in the formation of chemical bonds |
| model | a representation of an object or system |
| nucleus | the tiny, extremely dense, positively charged region in the center of an atom; made up of protons and neutrons |
| electron cloud | the region inside an atom where electrons are likely to be found |
| atomic mass unit | (amu) the SI unit used to express the masses of particles in atoms |
| neutrons | the particles of the nucleus that have no charge |
| protons | the positively charged particles of the nucleus; the number of protons in a nucleus is the atomic number that determines the identity of an element |
| atomic number | the number of protons in the nucleus of an atom |
| isotopes | atoms that have the same number of protons but have different numbers of neutrons |
| mass number | the sum of the protons and neutrons in an atom |
| atomic mass | the weighted average of the masses of all the naturally occurring isotopes of an element |
