Lesson 3.05

3.05 Ionic Bonding and Writing Formulas
Watch the following video about ions: http://bit.ly/YZkOWc
Then, draw a line from each word to its correct definition.
Ion • An atom or a group of atoms that form a charge by gaining or losing one or more electrons.
Monoatomic Ion
• An ion that has a positive charge
Polyatomic Ion
• Two or more atoms bonded together. Can have an overall charge of positive or negative.
Anion • An ion that has a negative charge
Cation
• An ion consisting of one element

Practice Determining Charge
Watch the video about common charges: http://bit.ly/YZkOWc
Download a periodic table with common charges here: http://bit.ly/XrbE70
a. Calcium: _____ b. Phosphorus: ____ c. Hydrogen: ____ d. Sulfur: _____ e. Aluminum: ____ f. Iodine: ______

Let’s Write That Formula

Ionic Compounds - Vocabulary
• Ionic Bonding – A chemical bond that is due to transfer of electrons between a cation (metal or H) and an anion (nonmetal).
• Ionic Compounds - A compound composed of positive and negative ions that are combined in a ratio where the positive and negative charges cancel out. Overall net charge is zero. The cation is always written first.
• Formula Unit - The formula of an ionic compound that represents the simplest whole number ratio of ions in the compound.

Writing Formula Units (Formulas) – The Basics
Example: Write the formula when calcium and phosphorus bond.
A. Write each ion
• The positive ion is always written first, then the negative ion.
B. Determine how many of each ion we need to make the compound neutral. That will be their subscripts.
• Subscripts must be the lowest whole number ratio.
• Make sure that the net charge of the formula is zero.

Writing Formula Units Practice
1) Aluminum and
Phosphorus
3) Bromine and Barium
2) Calcium and Lithium
4) Nitrogen and Fluorine

Writing Formula Units – Criss-Cross & Reduce Method
Write the formula that forms when the following pairs of elements form an ionic bond:
1. Potassium and Nitrogen 3. Magnesium and sulfur
2. Hydrogen and oxygen 4. Strontium and selenium

3.05 Comprehension Check
1. What is the common charge of a magnesium ion?
2. What is the formula that results when chlorine bonds with barium?
3. Identify three atoms that would lose two electrons to empty its valence energy level.
4. What subscripts are needed to complete the formula unit Al_N_?
5. Which of the following forms a cation?
a. Br b. Li C. N
6. Which of the following is a possible formula unit?
a. KN
3 b. I
3
N c. MgO

Thank You!
• It has been great working with you for Writing Ionic
Compounds! You will use this for the rest of module 3, module 4 and most of segment 2.
• Please use our other recorded teaching sessions for the other lessons. Don’t forget that you can use them to review previous lessons too!