IONIC AND COVALENT BONDS 8 th Grade Science

Case Study: The Hindenburg Myth Buster’s Mini Myth: shows/mythbusters/videos/hindenburg-minimyth.htmhttp://dsc.discovery.com/tv- shows/mythbusters/videos/hindenburg-minimyth.htm Blimps now use Helium instead of Hydrogen. Why?

Case Study: Hydrogen What do you notice about Hydrogen?

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 What do you notice about the Noble Gases?

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.

Ions What compound is being pictured ?

Ions Infer what has happened in these diagrams:

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

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  Why aren’t ions being formed?

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