The Universe

2. how much mass is contained in a specific volume
5. the fundamental force of attraction that pulls any objects with mass toward each other
6. an icy object that orbits the sun with a glowing tail, sometimes referred to as a "dirty snowball"
9. atoms of the same element with different numbers of neutrons
10. the particle that makes up protons and neutrons
11. substance consisting of only one type of atom and is define by its number of protons/atomic number
12. the most basic unit of matter that retains properties of an element
13. a testable explanation for an observation, sometimes called an "educated guess"
14. the theoretical point of infinite heat and density that was the origin of the universe
18. the particle that holds quarks together
19. an atom that has gained or lost electrons, changing its charge

1. a neutral particle found in the nucleus of an atom
3. the center of an atom made from protons and neutrons
4. the pathway that an electron travels
7. interstellar cloud of gas and dust where stars are born
8. a positively charged particle found in the nucleus of an atom, the number of which identifies what element the atom is
14. the star at the center of our solar system
15. a small rocky or metallic body that orbits the sun, often found between Mars and Jupiter
16. an explanation of observed phenomena that has been tested and is based on scientific fact/law
17. a negatively charged particle in an atom that orbits the nucleus