1. Atomic Theory Structure and Vocabulary

2. The Modern Atom Nucleus Electron Cloud

3. The Nucleus Protons: Positive Charge Neutrons: No Charge The Nucleus has a Positive Charge

4. Fact of Life: Nucleus Electron Cloud The number of Protons in the Nucleus is exactly equal to the number of Electrons in the Electron Cloud.

5. Vocabulary Definition: Atomic Number: Is strictly defined as the number of Protons in the nucleus of an atom. You can find the atomic number of an element on the periodic chart.

6. Task #1: Use your Periodic Chart to determine the number of protons for each of the elements given on the worksheet.

7. Fact of Life: Since the number of protons in the nucleus is equal to the number of electrons in the electron cloud, the number of Electrons is also given by the Atomic Number. But, do not define the Atomic Number as the number of electrons.

8. Task #2 Now fill in the number of electrons for each of the elements on the worksheet. You should notice too that there is a column asking you for the atomic number of each of the elements on the worksheet. You can fill these in too..

9. Vocabulary Definition: Mass Number: is defined as the sum of the protons and the neutrons in the nucleus of an atom. This value does not appear on the periodic chart. You must either be given the number of the protons and the neutrons and asked to calculate the mass number OR you must simply be given the mass number for the atom.

10. Fact of Life: It is possible (and quite common) for two atoms of the same element to have different mass numbers. This can occur because the number of neutrons in the nucleus is variable (means that it can change !!).

11. Example: Two atoms of Oxygen: Oxygen Atom #1 –8 Protons –8 Neutrons –It’s Atomic Number is 8. –Is Mass Number is 16. Oxygen Atom #2 –8 Protons –9 Neutrons –It’s Atomic Number is 8. –Its Mass Number is 17.

12. The atoms are described as ISOTOPES of the element Oxygen. They have the same atomic number. But they have different mass numbers because they have different numbers of neutrons.

13. Back to the Worksheet: The number connected to the name of the element is the mass number for that specific isotope. That means you are being told the total number of protons and neutrons in that specific atom. Now use that number and the atomic number (what info does the atomic number provide ?) to calculate the number of neutrons in each of the atoms given on the worksheet. Fill in the spaces.

14. Isotope Symbols: The Isotope Symbol is the chemist’s method of communicating the important information about a specific isotope. Sr 90 38 Atomic Symbol Mass Number Atomic Number The other way to represent this isotope would be Strontium – 90

15. Task #3: Now write the correct isotope symbol for each of the isotopes on this worksheet.