| A | B |
|---|
| mass number | the sum of the numbers of protons and neutrons in the nucleus of an atom |
| proton | subatomic particle that has a positive charge |
| ground state | the lowest energy state of a quantized system |
| electron configuration | the arrangement of electrons in an atom |
| Avogadro's number | the number of atoms or molecules in 1 mol (6.022 x 10^23) |
| excited state | a state i which an atom has more energy than it does at its ground state |
| atomic mass | the mass of an atom expressed in atomic mass units |
| orbital | a region in an atom where there is a high probability of finding electrons |
| nucleus | an atom's central region which is made of protons and neutrons |
| electron | subatomic particle that has a negative charge |
| mole | the SI base unit used to measure the amount of a substance whose number of particles equals the number of atoms of carbon in exactly 12g of carbon-12 |
| molar mass | the mass in grams of 1 mole of a substance |
| atomic number | the number of protons in the nucleus of an atom; it is the same for all atoms of an element |
| isotope | atoms that differ in the number of neutrons |
