Chapter 2 Matter is made up of Atoms Average Atomic Mass

Atomic Mass Atomic Mass: mass of an atom expressed in atomic mass units. Atomic Mass Unit: u = amu Average Atomic Mass   Mass found on the Periodic Table  average of the masses of the naturally occurring isotopes of each element. Weighted Average.

Atomic Mass Sample Problem  What is the atomic mass of copper if 69.17% of its atoms have a mass of 62.94 amu and 30.83% of its atoms have a mass of 64.93 amu?  

Atomic Mass Step 1: Change any percentage to decimal. (move decimal point two spots to the left.) Step 2: Multiply decimal by atomic mass. Step 3: Add Step 2 numbers together.

Atomic Mass Copper (Cu) 69.17% is 62.94 amu. 30.83% is 64.93 amu. Step 1 Step 2 Step 3 69.17% = 0.6917 30.83% = 0.3083 0.6917 x 62.94 0.3083 x 64.93 43.54 + 20.02 = 63.56 amu

Atomic Mass

Chapter 2 Matter is made up of Atoms Ions.

Recap No 1 – The Atom Proton Neutron Electron Charge +1 -1 Mass 1 amu -1 Mass 1 amu 0 amu Location Nucleus Orbit

Recap No 2 – Periodic Table Key Description Element Name Type of Atom Element Symbol Shorthand Atomic Number # p+ = # e- Atomic Mass # p+ and # n0

Recap No 3 – Isotopes Same number of protons and electrons. Different number of NEUTRONS. Isotope Protons Neutrons Mass Protium 1 Deutrium 2 Tritium 3

Recap No 4 - Atomic Mass Copper (Cu) 69.17% is 62.94 amu. Step 1 Step 2 Step 3 % to Decimal 69.17% = 0.6917 30.83% = 0.3083 Multiply by AMU 0.6917 x 62.94 0.3083 x 64.93 Add together 43.54 + 20.02 = 63.56 amu

Simple Ions. Ion: charged atoms. How does this happen? Add or remove electrons…

Simple Ions. Cation: Lose electrons; becomes positive. “Plussy Cat” Usually metals. “Plussy Cat”

Simple Ions. Anion: Gain electrons; becomes negative. “Ant-ion” Usually Nonmetals “Ant-ion”

Calculating #e- p+ = 8 e- = ? -2 p+ = 14 +4 10 10

Simple Ions Electrically charged atoms. Result from the gain or loss of an electron. Element + electron = negative charged element (anion) Element – electron = positive charged element (cation)

Ions Examples: 3 4 2 20 18 13 14 10 9 16 Lithium – Li +1 Ion Name Protons Neutrons Electrons Lithium – Li +1 3 4 2 Calcium – Ca +2 20 18 Aluminum – Al +3 13 14 10 Fluorine – F-1 9 Sulfur – S-2 16