Isotopes, e- config
 How can hydrogen
have an atomic mass
that is 1.00794?
 How is atomic mass
calculated?
Hydrogen Isotopes
 Isotope- atoms of the same element with different
numbers of neutrons
Answer
 Protium makes up 99.98% of all hydrogen atoms
 Atomic Mass is average mass based on abundance
Electron Configuration
 Electrons are distributed in energy shells around the
nucleus.
 Each shell holds a certain amount of electrons
 Why?
Energy Shell Electrons
 2/8/8/2 for the first 20 elements
Practice
 Example: Lithium, Atomic #3
 Sulfur, #16
 Carbon, # 6
 Calcium, # 20
Now-Just the Outer Shell!
 Lewis Dot Structure: Carbon
 Lithium:
 Sulfur:
 Calcium: