2. Atoms & Isotopes

3. ATOMS consist of 3 types of particles… Protons are positive charges Neutrons have no charge Electrons are negative charged + -

4. Protons & Neutrons in the middle… Electrons spin in a shell around them…

5. An ELEMENT is a pure substance made up of only one kind of atom. (Atom = element) A good example of an element is GOLD A bar of gold can be shaved into gold dust, an still be recognizable as gold. A bar of gold can be shaved into gold dust, an still be recognizable as gold. How fine can the dust become and still be considered gold?

6. Periodic Table of All Elements Element Name Element (letter) Symbol Atomic Number Atomic Mass (mass of all particles)

7. Elements differ from each other by the number of Protons in their center or nucleus. The Atomic Number, tells you how many protons are in each element.

8. So how many protons are in…. CARBON (C)6 PROTONS

9. The ATOMIC NUMBER will occasionally tell you the number of neutrons in the atom. ATOMIC NUMBER = for # of protons, electrons, and # of neutrons EX: Carbon, Nitrogen, and Oxygen Both Protons and Neutrons are found in the “nuclei” or center of the atom. (Electrons spin around on the outside)

10. If you add the Protons & Neutrons together you get the atoms: Mass Number – the sum of all the Protons and Neutrons in an atom.

11. Remember: the Mass number IS NOT the same as Atomic mass or Atomic number. Atomic Number = Number of Protons Mass Number= Sum of all protons & neutrons just in the nucleus of the atom Why is this important? Well I’ll show you… Atomic Mass = Weight of Protons, Neutrons, Electrons together

12. Sometimes you have elements with extra neutrons, or fewer neutrons than the number of protons. Atoms that are like this are called ISOTOPES. These have a tendency to be radioactive….

13. Let’s try a example…. How many Protons are in Carbon? So if you add them together your mass number would be 12. Carbon is sometimes called Carbon 12, by scientists when they are talking about the mass number. 6 Protons + 6 Neutrons How many Neutrons?

14. So how many protons & neutrons in the nucleus if Carbon is written in the form Carbon 14? Carbon 14 = 6 Protons, 8 Neutrons Radioactive dating of things like dinosaur bones is done by measuring the amount of Carbon 14 in the bone. What is the mass number for the element: Calcium 48? Calcium 48 = 20 Protons, 28 Neutrons

15. In some chemistry books you will see an element with a numbers written like this: C 6 17 Mass number Atomic number This is another way to write an isotope. Both methods are considered standards. So you must learn both. #of Neutrons = Mass Number – Atomic #

16. When asked how many neutrons in this element, how do you solve this? C 6 17 #of Neutrons = Mass Number – Atomic # - 11

17. An element of Chlorine has a mass number of 35. How many protons? How many neutrons? Chlorine is atomic number 17 This means there are 17 Protons, and the rest are neutrons. 35 – 17 = 18 Neutrons

18. An element of Sodium has 11 neutrons. How many Protons does it have? What is the mass number? Sodium has an atomic number of 11, so it has 11 protons. Since the mass number = Protons + Neutrons 11 + 11 = 22