Atomic Structure The Periodic Table, Isotopes, and Average Atomic Mass

Atomic Number Number of protons in an atom Periodic table is arranged by increasing atomic number The number of electrons in a neutral atom equals the number of protons in that atom

Reading the Periodic Table H Hydrogen Element Name Atomic Number Symbol Atomic Mass (amu)

Mass Number Sum of protons and neutrons in an atom NOT THE SAME AS ATOMIC MASS! H Hydrogen Cannot be found on periodic table NO NO NO NO NO!!!!

6 C Carbon Atomic Number Element Symbol Element Name Atomic Mass round this off to get Mass Number Reading the Periodic Table

Number of: Protons =Atomic Number Neutrons =Mass Number – Atomic Number Electrons =Atomic Number

Wrap-Up 1 Which of the following can be found on a periodic table? 1)Atomic number 2)Atomic mass 3)Mass number

What’s in a cheeseburger?

Isotope Atoms with same number of protons, but different number of neutrons HYDROGEN - 1 HYDROGEN - 2HYDROGEN - 3 = neutrons = protons = electrons

3 Different Hydrogen Isotopes HYDROGEN – 1 (protium) 1 proton 0 neutrons 1 electron HYDROGEN – 2 (deuterium) HYDROGEN – 3 (tritium) 1 proton 1 neutron 1 electron 1 proton 2 neutrons 1 electron

Ways to Write Isotopes 1) Hyphen notation (2 parts) name of element – # ORsymbol – # ex: carbon-14ORC-14 chlorine-35ORCl-35 hydrogen-3ORH-3 MASS NUMBER

Ways to Write Isotopes 2) Nuclear symbol (3 parts) C 14 6 element symbol mass number atomic number

Ex problem K Potassium # protons # neutrons # electrons Nuclear symbol Potassium-39 Potassium-40 Potassium K KK

Wrap Up 2 There are three common isotopes of carbon. The most prevalent has a mass of 12 amu. The other two have masses of 13 amu or 14 amu. Write the nuclear symbols for all three of these carbon isotopes.

Mass of Individual Atoms Atoms have extremely small masses (~1× kg) Instead we use a relative mass – atomic mass unit (amu) 1 amu ≈ mass of 1 proton or 1 neutron

Comparing Subatomic Particles particleMass (amu) e-p+n0e-p+n

Atomic Mass Weighted average mass of all isotopes of an element Where can it be found found on periodic table? K Potassium

Atomic Mass Recall all the hydrogen atoms in the world Hydrogen-1Hydrogen-2Hydrogen-3 Each has their own percent abundance in the world 99%0.2%0.8% Take averages of all the weights of each to find atomic mass atomic mass

Example: calculate atomic mass of chlorine Isotope mass (amu) percent abundance 35 Cl % 37 Cl %

Which isotope is most abundant? Ar-38, Ar-40, or Ar-41? Ar Argon Ar-40