1. DO NOW: Answer the following questions 1. What are the subatomic particles? 2. Where are each subatomic particle located? 3. What is the charge associated with each subatomic particle?

2.  Atom – the smallest particle of an element that can enter into a chemical reaction  Can be broken down into subatomic particles

3. REMEMBER  P….E….N

4. All atoms are composed of a dense nucleus surrounded by “empty” space occupied by electrons.

5. 1) The nucleus contains two types of particles; protons with a positive charge and neutrons with no charge. 2) The mass of a protons or a neutron is 1 amu. 3) The number of protons in the nucleus of an atom is the atomic number.

6. 4) For a neutral atom: atomic # = # protons = # of electrons 5) Each atom must contain the same number of protons but do not always contain the same number of neutrons 6) Electrons are located in orbitals outside the nucleus and have a charge equal to but opposite of, a proton.

7. 7) The sum of the number of protons and neutrons in the nucleus is called the mass number. Ex: Mass # - # of protons = # of neutrons Ex: Mass # - # of neutrons = # of protons

8. 8) A neutral atom of Magnesium (Mg) contains 12 protons and 12electrons. 9) When the mass # of a neutral atom of Sulfur (S) is 30 then the number of protons / electrons is 16 and the # of neutrons is 14.

9. Element NameSymbolAtomic #AMU# of Protons # of Electrons # of Neutrons K19 5 16 23 10 48 25 1415

10. 1) All atoms of a given element must contain the same # of protons but the # of neutrons may vary. 2) Isotopes are atoms of the same element that have different #s of neutrons, and hence have different mass numbers.

11. 3) Isotopes are identified by using a symbol that indicates both the element and its mass number. 4) The mass number of any given element must be an integer because it is the sum of all protons and neutrons

14. 5. The average atomic mass is the weighted average of all the isotopes of a given element and is the number in the top left corner of each element on the Periodic Table.

15. 1. 80% 127 I, 17% 126 I, 3% 128 I

16. 2. 50% 197 Au, 50% 198 Au

17. Nucleons: particles in the nucleus (protons and neutrons) Nuclear Charge: charge of the nucleus (same at # of protons) Examples: 1. How many nucleons are there in an atom with an atomic number of 20 and 23 neutrons? 2. What is the nuclear charge of an Iron atom?