1. Section 2: Atoms, Bonding, and the Periodic Table
Mr. Gardner 7th Grade Science

2. Key Concepts
How is the reactivity of elements related to valence electrons in atoms?
What does the periodic table tell you about atoms and the properties of elements

3. Key terms Valence Electrons Electron dot diagram Chemical bond Symbol
Atomic number
Period
Group
Family
Noble gas
Halogen
Alkali metal

5. How the Periodic Table Works
Oxygen has:
8 electrons
8 protons
An atomic mass of rounded to 16
Neutrons: 16-8=8

6. Valence Electrons Valence Electrons:
Have the highest energy level and are held most loosely.
Outermost electrons
The number of valence electrons determines the properties of that element.
This is how they bond together
The easiest way to represent electrons is the Electron Dot Diagram:
Element symbol surrounded by the number of valence electrons

7. Chemical Bonds and Stability
Atoms want 8 electrons in their valence shell
Some atoms live with 8 electrons.
These are not reactive.
Noble Gases: all elements in group 18 on the periodic table.
Some really want balance in life
Halogens: atoms with seven valence electrons
React very easily by excepting an electron.
Alkali Metals: Atoms with one valence electron
Reacts very easily by giving an electron.