20 Hard

2. The elements in group 17 of the periodic table.
4. The chemical name for common salt.
6. The element that is in the fourth period and in the sixth group.
7. The emission of electrons from a metal when light shines on the metal.
8. The arrangement of electrons in an atom.
11. A three-dimensional region around the nucleus that indicates the probable location of an electron.
14. The state in which an atom has a higher potential energy than it has in its ground state.
15. The range of 400nm to 700nm on the electromagnetic spectrum.
18. One amu stands for ___________.
19. The element that has the atomic number of 28.

1. A general term for any isotope of any element.
2. The electron-containing main energy level with the highest principal quantum number.
3. The element with the average atomic mass of 12.011.
5. The gas that is being given off when an egg's shell is put into vinegar.
9. According to ____________ an electron occupies the lowest-energy orbital that can receive.
10. The elements in group 18 of the periodic table.
12. The smallest unit of an element that maintains the properties of that element.
13. The lowest energy state of an atom.
16. A hydrogen atom with one proton and no neutrons.
17. the minimum quantity of energy that can be lost or gained by an atom.