| A | B |
|---|
| atom | the smallest piece of an element that has the properties of that element |
| nucleus | the central core of an atom |
| element | matter made of only one kind of atom |
| compound | matter made of atoms of two or more elements |
| mixture | a blend of elements, compounds, or both |
| crystal | particles packed together in a repeating order or pattern |
| melting point | the temperature at which a solid becomes a liquid |
| evaporation | the change of a liquid into a gas at its surface |
| boiling point | the temperature at which all of a liquid changes to a gas |
| freezing point | the temperature at which a liquid becomes a solid |
| condensation | the process in which a gas changes to a liquid |
| troposphere | the layer of the atmosphere closest to Earth's surface |
| air pressure | the weight of the air pressing down on an area of Earth |
| barometer | an instrument used to measure air pressure |
| thermometer | an instrument used to measure temperature |
| wind | the horizontal movement of air from one place to another |
| anemometer | an instrument used to measure wind speed |
| wind vane | an instrument used to show which way the wind is blowing |
| relative humidity | the amount of water vapor a volume of air is holding compared to the greatest amount it can hold at a given temperature |
| dew point | the temperature at which water vapor condenses |
| precipitation | moisture returning to Earth from the atmosphere |
| fog | a stratus cloud close to the ground |
