1. Atomic Number The number of protons in an atom Also, the number of electrons in a neutral atom

2. atomic numberatomic number atomic number 1 6 79

3. Atomic Mass The number of protons + neutrons in the nucleus Since the mass of an electron is soooo much smaller than the mass of protons or neutrons, we do not include it in the atomic mass

5. Showing atomic number and mass 7 Li 3 3 protons 3 electrons 7-3 = 4 neutrons

6. How many protons, neutrons, & electrons?

8. Ion An atom that has gained an electron is called an anion. It has a net negative charge. An atom that has lost an electron is called a cation. It has a net positive charge.

9. Isotope Atoms of the same element that have different atomic masses (but same atomic number) WHY do they have different atomic masses?

10. Isotope If two atoms are of same element, they MUST have the same number of protons (the same atomic number) But…. they can have different number of NEUTRONS. The more neutrons, the heavier the atom

11. Hydrogen Hydrogen is the smallest atom. Most hydrogen atoms have only one proton and one electron (no neutrons) 1 H 1

12. One isotope of Hydrogen has a neutron

13. Another isotopes of Hydrogen has 2 neutrons

14. Isotopes of Hydrogen

16. Isotopes of Lithium 3 neutrons 4 neutrons 5 neutrons

17. Isotopes of carbon