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IONIC COMPOUNDS
Recall: Metals form positive ions (+) and non-metals form negative ions (-).
Na
1+ Cl
1-
IONIC COMPOUNDS When ions like NaCl form, they make
an ionic bond.
Ionic bond – the attraction between a positive metal ion and a negative non-metal ion.
Na
1+ Cl
1-
Like most ionic compounds, NaCl can form a crystalline structure
Just like most things in nature, these
Na
1+ Cl
1-
NaCl
Ionic bonds
Ionic compounds have certain characteristics because of their ionic bonds: Most are crystalline solids at room
temperature. Ionic compounds generally have high
melting points. Can conduct an electric current when
dissolved in water (electricity can “jump” between the negative and positive charges).
Just like most things in nature, the charges in ionic compounds must balance out. Ex. Sodium ion is 1+, Chloride ion is 1-
so they balance out. What about calcium and chloride?
Na
1+ Cl
1-
NaCl
Calcium atom becomes Calcium ion with a charge of _____.
Chlorine atom becomes Chloride ion with a charge of _____.
So how will they form a compound?
One calcium ion will bond with two chloride ions so that the charges balance out.
2+
1-
Ca2+
Cl -Cl -
CaCl2
WRITING FORMULAS OF IONIC COMPOUNDS
EXAMPLE 1- What is the formula for the ionic compound of calcium and fluorine?
Step 1 – Write the symbols of the elements with the metal first and non-metal second
Ca FStep 2 – Write the ion charge of each
element Ca2+ F-1
Step 3 – Determine how many of each
you need to have an overall charge of zero.
Ca+2 F-1 F-1
Step 4 - Write the formula using subscripts, after the element, to indicate how many you used.
Ca1F2 CaF2 ( 1 is not needed )
EXAMPLE 2
What is the formula for the ionic compound of aluminum and sulfur?
Steps:1) Al S2) Al+3 S-2
3) Al+3 Al+3 S-2 S-2 S-2
4) Al2S3
WRITING NAMES OF IONIC COMPOUNDS
When naming an ionic compound we simply write the name of the metal first and non-metal second. We change the ending of the non-metal name so that it ends in “ide.”