Chemical Bonds Physical Science Chapter 20

Chemical bonds A chemical bond is the force that holds atoms together in a compound.

Chemical Formulas A chemical formula tells what elements a compound contains and the exact amount of the atoms of each element in a unit of that compound What elements and how many of each are in the following? HCl (hydrochloric acid) CH 3 COOH (vinegar) C 12 H 22 O 11 (sucrose)

Atomic Stability An atom is chemically stable when its outer energy level is full Octet rule: atoms tend to gain, lose or share electrons to have eight electrons in their outer electron shell Which group of elements already has eight electrons in their outer shell?

Ionic Bonds Electron sharing

Ions An ion is formed when an atoms gains or loses an electron. If it gains an electron it becomes negative If it loses an electron it becomes positive

Oxidation number Oxidation number tells you how many electrons an atom has gained, lost, or shared to become stable Ionic compounds – same as the charge of the ion “1 plus, 2 plus, 3 plus, SKIP, 3 minus, 2 minus, 1 minus ZIP”

Ionic Bond Ionic bond is the force of attraction between the opposite charges of the ions Forms between a metal and a nonmetal Electrons are transferred

Writing Ionic Compounds What is the chemical formula for Sodium andOxygen? Steps to take: 1. Determine atomic symbol and oxidation number for each element: Sodium = Na 1+ Oxygen = O “Swap and Drop” – The oxidation number becomes the subscript for the other element Na 1+ O 2- Na 2 O 3. Other things to know: Subscripts do not have a charge (so don’t write the + or -) You do not write “1” as a subscript – it is understood that there is “1” there If the oxidations add up to zero then you just write the symbols, no subscripts.

Practice writing formulas 1. Sodium and Chlorine 2. Potassium and Oxygen 3. Calcium and Fluorine

Writing names of binary ionic compounds 1. Write the name of the positive ion 2. Write the root name of the negative ion. The root is the first part of the element’s name.  Example: Chlorine would be chlor- 3. Add the ending –ide to the root.  A few special elements: Oxygen = oxide Phosphorus = phosphide Nitrogen = nitride Sulfur = sulfide Important note: Subscripts do not become part of the name for ionic compounds.

Practice Naming Ionic Binary Compounds 1. NaCl 2. K Calcium and Fluorine 4. MgO Binary Compounds=compounds made of 2 elements

Transition Metals 0 Transition metals have more than 1 oxidation number and this must be described in the compound name. 0 Use parentheses to tell which form of the element you are talking about. 0 Copper oxygen = copper (III) oxide 0 Copper +4 + oxygen = copper (IV) oxide 0 Oxidation number = number of electrons 0 Subscript = number of atoms

More Hints- Ionic Compounds 0 Most compounds are binary. 0 Write the full name of the cation (positive ion) and the root of the anion (negative ion) 0 Charges must = 0 0 Oxidations number are indicated by Roman numbers in the names Cupper (II) chloride Copper (I) chloride

Activity: Bond With a Classmate 0 Each blank should have different compounds. 0 You cannot bond with the same element twice. 0 Work together to figure out how to do that formula and name. 0 If you simply copy the answer you will not understand what to do. 0 You have minutes to complete each section. 0 Bring to me to spot check when done. 0 Sit down and wait.