| A | B |
|---|
| Dalton's Atomic Theory | 1. All elements are composed of tiny indivisible particles called atoms. 2. Atoms of the same element are indentical. The atoms of any one element are different from those of any other element. 3. Atoms of different elements can physically mix together or can chemically combine with one another in simple whole-number ratios to form compounds. 4. Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction. |
| Electrons | Negatively charged subatomic particles. |
| J. J. Thomson | Discovered electrons in 1897 using cathode rays. |
| Robert A. Millikan | Carried out experiments that let him find the quantity of charge held by electrons. He also calculated the mass of the electron, which is very similar to that accepted today. |
| Protons | Positively charged subatomic particles. |
| E. Goldstein | Discovered protons |
| James Chadwick | Discovered neutrons |
| Neutrons | Subatomic particles with no charge but a mass nearly equal to that of a proton. |
| Ernest Rutherford | Discovered the nucleus. |
| Nucleus | The central core of the atom and is composed of protons and neutrons. |
| Atomic Number | The number of protons in the nulceus of an atom of that element. |
| Mass Number | The total number of protons and neutrons in an atom. |
| Isotopes | Atoms that have the same number of protons but different numbers of neutrons. |
| Dmitri Mendeleev | Created the first periodic table by arranging the known elements in columns by increasing atomic mass. |
| Metals | Are lustrous, malleable, ductile, and conduct electricity and heat. |
| Nonmetals | Aren't lustrous, malleable, or ductile and don't conduct heat and electricity. |
| Metalloids | Have properties of metals and nonmetals. |
