| A | B |
|---|
| nucleus | the positively charged center of an atom |
| electron | negatively charged particles that move around the nucleus |
| proton | positively charged particle in the nucleus |
| neutron | particle in the nucleus with a neutral charge |
| atomic number | the number of protons in the nucleus of an element |
| electron cloud | the region in whick electrons move |
| quark | the smaller particles that make up protons and neutrons |
| mass number | the sum of the number of protons and neutrons in the nucleus |
| isotopes | atoms of the same element that have different numbers of neutrons |
| periodic table | the arrangement of elements according to repeated changes in properties |
| atoms | the basic building blocks of matter |
