HISTORY OF ATOMS AND ELEMENTS

3. Discovered the electron using a cathode ray tube.
4. horizontal row in the Periodic Table of Elements.
5. General term for parts of the atom like protons, neutrons, and electrons.
6. basic unit of a chemical element.
8. Proposed the first modern atomic theory.
10. SI unit for amount of substance.
13. What element has an electron configuration of [Ne]3s^2 3p^5?
16. An atom or molecule with a net electric charge due to loss or gain of electrons.
17. Proposed that all matter is composed of four "roots": Earth, Air, Fire, and Water.
20. Established that elements should be arranged by atomic number, not mass.
22. Group 17 elements; highly reactive nonmetals.
23. What element has an electron configuration of [Ne]3s^2 3p^4?
25. A subatomic particle with no electric charge found in the nucleus.
26. Proposed that electrons orbit the nucleus in specific energy levels.
28. Determined the number of particles in one mole (6.022 x 10^23).
29. The current, mathematically-based description of electron location.

1. The total mass of protons and neutrons in an atom's nucleus.
2. Greek philosopher associated with the idea of four elements.
4. A tabular arrangement of chemical elements by atomic number.
7. Russian chemist who created the first widely accepted periodic table.
9. A region of space where an electron is most likely to be found.
11. A pre-Socratic philosopher who proposed everything is infinitely divisible.
12. Credited as the first to use medicine for human healing.
14. The ancient practice of turning base metals into gold.
15. positively charged subatomic particle found in the nucleus.
18. negatively charged subatomic particle that orbits the nucleus.
19. Described the atom as a small, dense nucleus orbited by electrons.
21. The dense center of the atom containing protons and neutrons.
24. The specific regions around the nucleus where electrons travel.
27. Atoms of the same element with different numbers of neutrons.