1. 1Chemistry Chapter 4: How Atoms Differ: Atomic number = # p + AND e - (assume neutral atom for charge). Atomic number = # p + AND e - (assume neutral atom for charge). Rounded (whole number) mass number = # p + + # n 0. Rounded (whole number) mass number = # p + + # n 0. Rounded average mass number – Atomic number = #n 0. Rounded average mass number – Atomic number = #n 0. Symbol notation (Element; mass # and atomic #). Symbol notation (Element; mass # and atomic #).

2. 2Chemistry Ions: When atoms are NOT balanced for charge they are called ions. Positive ion: Atom has lost electrons. Called cations (symbol). Positive ion: Atom has lost electrons. Called cations (symbol). Negative ion: Atom has gained electrons. Called anions (symbol). Negative ion: Atom has gained electrons. Called anions (symbol). Symbol system for ions. Symbol system for ions.

3. 3Chemistry Isotopes: When the number of neutrons is different BUT the proton number is the same…: Chemical behavior is the same.Chemical behavior is the same. The more neutrons, the greater the mass number (mass).The more neutrons, the greater the mass number (mass). Most elements found in nature are a mixture of isotopes.Most elements found in nature are a mixture of isotopes. Isotopes differ for their relative abundance in nature (show as a %).Isotopes differ for their relative abundance in nature (show as a %).

4. 4Chemistry Atomic and Mass # Review: – The atomic number provides the number of protons in the nucleus and the number of electrons in a neutral atom. – The mass number tells us the number of protons and neutrons in the nucleus. The mass # minus the atomic # provides the number of neutrons. The mass # is different for isotopes of the same element.

5. 5Chemistry Isotopes and Ions Review: – Different isotopes of the same element that are neutral for charge are different for neutron # and mass #; they are the same for electron # and proton #. – Ions of the same element are different for electron # and charge ; they are the same for atomic # and mass #. – Cations have a positive charge because electrons have left the atom. Anions have a negative charge because electrons have entered into the atom.

6. 6Chemistry Average Atomic Mass: – Chemists used a standard of C-12 as being 12 amu; 1 amu is 1/12 of C-12. – Calculating average atomic mass  need number of naturally occurring isotopes, their masses AND their abundance (percentage of the total found in the environment).

7. 7Chemistry Average Atomic Mass: –Round I: Calculate the atomic mass of element X and identify the element from the periodic table using the following data: 63 X (62.930 amu; 69.2% abundance). 63 X (62.930 amu; 69.2% abundance). 65 X (64.928 amu; 30.8%) 65 X (64.928 amu; 30.8%) – Answer: 63.5 amu; Copper (Cu)

8. 8Chemistry Average Atomic Mass: – Round II: Calculate the atomic mass of element Y and identify the element from the periodic table using the following data: 54 Y (53.940 amu; 5.9% abundance). 54 Y (53.940 amu; 5.9% abundance). 56 Y (55.935 amu; 91.72%) 56 Y (55.935 amu; 91.72%) 57 Y (56.935 amu; 2.1% abundance) 57 Y (56.935 amu; 2.1% abundance) 58 Y (57.933 amu; 0.28% abundance). 58 Y (57.933 amu; 0.28% abundance). – Answer: 55.844 amu; Iron (Fe)