Chemical BondsPhysical 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)• CH3COOH (vinegar)

• C12H22O11 (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 BondsElectron 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 CompoundsWhat is the chemical formula for Sodium and Oxygen?

Steps to take:1. Determine atomic symbol and oxidation number for each element:

Sodium = Na1+ Oxygen = O2-

2. “Swap and Drop” – The oxidation number becomes the subscript for the other element

Na1+ O2-

Na2 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 Chlorine2. Potassium and Oxygen3. Calcium and Fluorine

Writing names of binary ionic compounds

1. Write the name of the positive ion2. 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 = oxidePhosphorus = phosphideNitrogen = nitrideSulfur = sulfide

Important note: Subscripts do not become part of the name for ionic compounds.

Practice Naming Ionic Binary Compounds

1. NaCl2. K20

3. Calcium and Fluorine4. MgO

Binary Compounds=compounds made of 2 elements

Transition Metals0Transition metals have more than 1 oxidation number

and this must be described in the compound name.0Use parentheses to tell which form of the element you

are talking about.0Copper + 3 + oxygen = copper (III) oxide0Copper +4 + oxygen = copper (IV) oxide

0Oxidation number = number of electrons0Subscript = number of atoms

More Hints- Ionic Compounds0Most compounds are binary.0Write the full name of the cation (positive ion) and the

root of the anion (negative ion)0Charges must = 00Oxidations number are indicated by Roman numbers

in the names Cupper (II) chloride Copper (I) chloride

Activity: Bond With a Classmate

0Each blank should have different compounds.0You cannot bond with the same element twice.0Work 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.0You have 10-15 minutes to complete each section.0Bring to me to spot check when done. 0Sit down and wait.