Chemistry Ch. 4

5. English chemist and schoolteacher who formulated a theory to describe the structure and chemical reactivity of matter in terms of atoms
9. an instrument used to generate images of individual atoms
14. Greek philosopher who was among the first to suggest the existence of atoms
15. atoms that have the same number of protons but different numbers of neutrons
16. positively charged subatomic particles
17. the smallest particle of an element that retains its identity in a chemical reaction

1. an arrangement of elements according to similarities in their properties
2. stream of electrons produced at the negative electrode of a tube containing a gas at low pressure
3. the number of protons in the nucleus of an atom of an element
4. negatively charged subatomic particles
6. equals the number of neutrons plus the number of protons in an atom
7. one-twelth the mass of a carbon-12 atom
8. a vertical column of elements in the periodic table
10. subatomic particles with no charge
11. the central core of an atom, which is composed of protons and neutrons
12. a horizontal row of the periodic table
13. weighted average mass of the atoms in a naturally occurring sample of an element