| A | B |
|---|
| Element | a substance that cannot be broken down into simpler substances by physical or chemical means |
| Atom | the smallest particle of an element that has all of the characteristics of that element |
| Nucleus | the positively charged center of an atom |
| Proton | a tiny particle that has mass and a positive electrical charge |
| Neutron | a particle with about the same mass as a proton |
| Atomic number | the number of protons in an atom's nucleus |
| Mass number | the combined number of protons and neutrons |
| Electron | tiny atomic particle with little mass and a negative electrical charge that surrounds the nucleus in energy levels |
| Energy level | represents the area in an atom where electrons are most likely to occur |
| Valence electrons | the electrons in the outermost energy level which determine the chemical behavior of the different elements |
| Isotopes | atoms of the same element that have different mass numbers |
| Atomic mass | the average of the mass numbers of the isotopes of an element |
| Radioactivity | the spontaneous process through which unstable nuclei emit radiation |
| Compound | a substance that is composed of atoms of two or more different elements that are chemically combined |
| Chemical bonds | the forces that hold the elements together in a compound |
| Covalent bond | attraction of two atoms for a shared pair of electrons that holds the atoms together |
| Molecule | combination of two or more atoms joined by covalent bonds |
| Ion | an electrically charged atom or group of atoms that gains or loses an electron from their outermost energy levels |
| Ionic bond | the attractive force between two ions of opposite charge |
| Chemical reaction | the change of one or more substances into other substances (chemical reactions are described by chemical equations) |
| Solution | homogeneous mixture whose components cannot be distinguished and can be classified as liquid |
| Acid | a solution containing a substance that produces hydrogen ions (H+) in water |
| Base | solution that contains hydroxide ions (O-) |
| Crystalline structure | regular geometric pattern of particles in most solids |
| Glass | solid that consists of densely packed atoms with a random arrangement and lacks crystals or has crystals that are not visible |
| Evaporation | process of changing from a liquid to a gas (also called vaporization) |
| Sublimation | change of state from a solid to a gas |
| Plasma | hot |
| Condensation | process by which a cooling gas changes into a liquid and releases thermal energy |
