1. Chemistry

2.  Atomic Number  Mass Number  Isotopes  Atomic mass unit  Atomic mass

3.  Elements are diff because they contain diff #’s of protons  ATOMIC NUMBER: # of protons in the nucleus of an atom of that element

4.  Atomic # of H is 1  Every hydrogen atom has 1 proton  Number of neutrons can vary, but H always has 1 proton  Atomic number of gold (Au)? Atomic number

5.  In a neutrally charged atom of an element, the # of p + = e -  How many electrons in neutral oxygen (O)? Neutral Sodium (Na)?  Complete practice problems 15 and 16 on page 111 in your notes

6.  Most of mass of an atom found in nucleus (p + and n 0 )  MASS NUMBER: The total number of p + and n 0

7.  To determine the number of n 0 :  # of n 0 = mass number – atomic number  How many neutrons in Magnesium (Mg) if the mass number is 24?  2 Shorthand ways of representing an element Mass number

8.  ISOTOPES: Atoms that have the same number of protons but different number of neutrons  Different number of neutrons means diff mass number  3 isotopes of hydrogen  Hydrogen - 1 (Protium)H  Hydrogen - 2 (Deuterium)H  Hydrogen - 3 (Tritium)H

9.  All versions of an element are chemically alike

10.  Mass of a proton or neutron = 1.67 x 10 -24 g  Small size impractical to work with  ATOMIC MASS UNIT (AMU): One-twelfth the mass of a carbon-12 atom  Carbon -12 has 6 p + and 6 n 0  1 p + or 1 n 0 has a mass of 1 amu

11.  Masses of elements not whole numbers  Isotopes of an element are found in different abundance  Page 114  Most hydrogen is hydrogen-1

12.  ATOMIC MASS: A weighted, average mass of the atoms in a naturally occurring sample of the element  Reflects both mass and relative abundance of the isotopes  Similar to how your grades are calculated in my class  To determine the atomic mass of an element, multiply the mass of each isotope by it’s natural abundance, expressed as a decimal, and then add the products

13.  Go to Distinguishing Among Atoms Addition

14.  Do practice problems 23 and 24 on page 117 in your notes

15.  Pg 122 – 123  Problems 34, 39 - 41, 44, 46-50, 52 - 55, 65  Don’t write the questions  Write this problem down:  There are two main isotopes of indium: indium – 114 with an abundance of 85.5%, indium - 115 with an abundance of 9.50%, and indium – 116 with an abundance of 5.00%. What is the atomic mass of indium?