Across
- 2. the gases ar the Earth
- 4. a chemical that combines two or more elements:
- 7. the simplest unit of a chemical substance, usually a group of two or more atoms
Down
- 1. the number of times that a light wave (or a sound wave or a radio wave) vibrates (moves up and down)
- 3. the line where the sky and the land or sea seem to meet
- 5. a single living plant, animal, virus, etc...
- 6. to move quickly in different directions