1. Ionic Bonding and Writing Formulas
Lesson 3.05
Ionic Bonding and Writing Formulas

2. 3.05 Ionic Bonding and Writing Formulas
Watch the following video about ions:
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
Two or more atoms bonded together. Can have an overall charge of positive or negative.
Polyatomic Ion
Anion
An ion that has a negative charge
Cation
An ion consisting of one element

3. Practice Determining Charge
Watch the video about common charges:
Download a periodic table with common charges here:
What is the common charge for:
a. Calcium: _____
b. Phosphorus: ____
c. Hydrogen: ____
d. Sulfur: _____
e. Aluminum: ____
f. Iodine: ______

4. Let’s Write That Formula
Ionic Compound
Cation & Anion
(+ is always written first)
Overall charge of formula unit is zero
How many ions of each element you need is its subscript

5. 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.

6. Writing Formula Units (Formulas) – The Basics
Example: Write the formula when calcium and phosphorus bond.
Write each ion
The positive ion is always written first, then the negative ion.
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.
Check your work
Make sure that the net charge of the formula is zero.

7. Writing Formula Units Practice
Aluminum and Phosphorus
Calcium and Lithium
Bromine and Barium
Nitrogen and Fluorine

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

9. 3.05 Comprehension Check What is the common charge of a magnesium ion?
What is the formula that results when chlorine bonds with barium?
Identify three atoms that would lose two electrons to empty its valence energy level.
What subscripts are needed to complete the formula unit Al_N_?
Which of the following forms a cation?
Br b. Li C. N
Which of the following is a possible formula unit?
KN3 b. I3N c. MgO

10. 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!