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Case Study: The Hindenburg Myth Buster’s Mini Myth: http://dsc.discovery.com/tv-shows/mythbusters/videos/hindenburg-minimyth.htm
Blimps now use Helium instead of Hydrogen. Why?
Case Study: Hydrogen
Most abundant chemical substance Colorless, odorless, tasteless, non-toxic,
highly combustible gas Very high chemical reaction
Why? It only has one valence electron Readily combines and forms Covalent Bonds
Case Study: Noble Gases
He, Ne, Ar, Kr, Xe, Rn Odorless, colorless, gases Very low chemical reactivity
Why? Their outer shell of valence electrons are
considered “full” Gives little tendency to participate in chemical
reactions
Case Study Conclusion
Stable-Atoms are “happy” when they have full energy levels.
Having an uneven amount of valence electrons causes atoms to react with one another.
Octet Rule: atoms will combine with each other in order to have eight valence electrons like a noble gas.
Review: Ions
Ions have a charge Cation: loses an electron
Positive charge Anion: gains an electron
Negative charge
Which element is a cation? Which is an Anion?
Ionic Bonds- Loss or Gain
Ionic Bonds: the bonds that hold ions together
Compound: a pure substance containing two or more elements
Ionic Bonds- Loss or Gain
Infer what has happened in this picture
Compounds can be created many ways by losing more then one electron or gaining more then one electron.
Covalent Bonds- Sharing
Certain atoms cannot lose or gain electrons, because it is to difficult and takes so much energy.
Covalent Bonds- Sharing
Covalent Bond- the chemical bond that forms between nonmetal atoms when they share electrons
The shared electrons are attracted to the nuclei of both atoms
Covalently bonded compounds are called molecule compounds.
Molecule: a neutral particle formed when atoms share electrons
Covalent Bonds- Sharing
Double Bond: when two pairs of electrons are shared
Triple Bond: when three pairs of electrons are shared
Periodic Table Trend
• Covalent Bond is when two non-metals bond together.
• Ionic Bond is when a metal and a non-metal bond together.
Covalent Bonds- Sharing
Double Bond: when two pairs of electrons are shared
Triple Bond: when three pairs of electrons are shared
Chemical Formulas
Chemicals are represented by letters Some symbols are the first letter of their name Some symbols are the first letters of their name
in another language Potassium is K, in latin potassium is kalium
Compounds are shown using symbols and numbers the subscript illustrates how many atoms are in the
molecule Chemical formula:
a mathematical sequence that expresses a chemical reaction
Combination of chemical symbols and numbers that show which elements are present in a compound