| A | B |
|---|
| atomic mass | weighted average of the mass number of an element's naturally occurring isotopes |
| atomic mass unit | a unit used to measure the masses of subatomic particles |
| proton's amu | 1 amu |
| atomic number | number of protons in the nucleus of an atom |
| electromagnetic force | force of attraction or repulsion between particles in an atom |
| electron | negatively charged subatomic particle found in an area outside the nucleus of an atom |
| electron's charge | negative |
| electron cloud | space in which electrons are likely to be found |
| energy level | most likely location an electron can be found |
| gravity | force of attraction that depends on the mass of two objects and the distance between them; responsible for accerating an object toward the earth |
| isotope | atom that has the same numbers of protons as another atom but a different number of neutrons |
| mass number | sum of the protons and neutrons in the nucleus of an atom |
| neutron | subatomic particle with no charge located in the nucleus of an atom |
| neutron's charge | neutral |
| nucleus | a small, dense, positively charged center of an atom |
| proton | postively charged subatomic particles located in the nucleus of an atom |
| proton's charge | positive |
| quark | particle that makes up all other known particles in the nucleus of an atom |
| strong force | force that binds protons and neutrons in the nucleus |
| subatomic particles | protons, neutrons, and electrons |
| weak force | force that is the key to how power of the sum; responsible for a process known as radioactive decay |
| Democritus | Atoms are small, hard particles. |
| An atom is the smallest piece of matter. | Democritus |
| Thomson | An atom contains negatively charged particles called "corpuscles." |
| An atom is made of positively charged "pudding-like" material through which negatively charged particles are scattered. | Thomson |
| Dalton | Atoms of the same element are exactly alike. |
| Atoms are indivisible. | Dalton |
| Bohr | In an atom, electrons move in definite orbits around the nucleus, much like the planets circle the sun. |
| In an atom, electrons are located in the energy levels that are a certain distance from the nucleus. | Bohr |
| Rutherford | An atom is mostly empty space with a dense, positively charged nucleus in the center. |
| Wave model | An atom has a small, postively charged nucleus surrounded by a large region in which scientists can predict where an electron is likely to be found. |
| The discovery of the electron by J.J. Thomson proved that | the atom is divisible. |
| According to the theory of wave mechanics | the exact location of an electron is impossible to determine. |
| Protons and neutrons are found | in the nucleus. |
| Electromagnetic, stong, weak, and gravity | the four forces that govern the behavior of subatomic particles. |
