Transcript PS 22.3 A Notes - Ionic Formulas

22.3 – Writing formulas for
Ionic Compounds
Part A
Focus on what is in PINK
Objectives

Write formulas for ionic compounds
Writing Ionic Formulas

Watch the Tyler DeWitt Video and
complete the viewing guide, you will
add it to your notes on this chapter
Youtube video
Binary Ionic Compounds
• A compound composed of 2 elements
• To write a chemical formula for a
binary compound, you need to know:
• which elements are involved
• how many electrons they lose or gain to
become stable
Ionic Compounds are
NEUTRAL
• Although the individual ions in a
compound carry charges, the
compound itself is neutral
• A formula must have the right number
of positive ions and the right number of
negative ions so the charges balance
Oxidation Number

The number of electrons an atom must
gain, lose or share to become stable


Cations = lose electrons
Anions = gain electrons
Oxidation Number

Determined by which group the
element is in and how many valence
electrons it has

Valence electrons = The BONDING
electrons found in the outermost
energy level
Oxidation Number

Group 1 = 1 valence electron



Group 2 = 2 valence electron



Loses 1 e- to become stable
Ion = +1 charge
Loses 2 e- to become stable
Ion = +2 charge
Group 3 = 3 valence electron


Loses 3 e- to become stable
Ion = +3 charge
Oxidation Number


Groups 3-12 = Transition metals =
variable # of electrons, unpredictable
charges
Group 13 = 3 valence electron


Loses 3 e- to become stable
Ion = +3 charge
Oxidation Number

Group 14 = 4 valence electron



Group 15 = 5 valence electron



Can gain or lose 4e- to become stable
Ion = ±4 charge
Gains 3e- to become stable
Ion = -3 charge
Group 16 = 6 valence electron


Gains 2e- to become stable
Ion = -2 charge
Oxidation Number

Group 17 = 7 valence electron



Gains 1e- to become stable
Ion = -1 charge
Group 18 = *8 valence electron


STABLE
No charge, no ions
Oxidation #/Charges of Ions
Write Formulas for these ions

Potassium ion K+

Magnesium ion Mg
2+

Oxide (oxygen) ion
O 2-
Transition Elements
• Can have multiple oxidation
numbers
• Express using Roman
numerals
• For example, the oxidation
number of iron in
iron (III) oxide is 3+.
Write Formulas for these ions

Copper (I) ion

Chromium (VI) ion

Mercury (II) ion
Cu 1+
Cr 6+
Hg 2+
Step By Step – Writing Formulas
1. Write the symbol of the element with the
positive oxidation number or charge
2. Write the symbol of the element with the
negative oxidation number or charge
3. The charge (without the sign) of one ion
becomes the subscript of the other ion.
•
Reduce the subscripts to the smallest whole
numbers that retain the ratio of ions.
Criss-Cross Method
Writing Formulas

Write the formula for calcium chloride.


Calcium is Ca+2
Chloride is Cl-1
Ca+2 Cl-1
Cl-1
CaCl2
In-Class Assignment/Homework

PS 22.3 A WKT 1 - Criss Cross practice