WHAT IS AN IONIC REACTION?

WHAT IS AN IONIC REACTION?

A CHEMICAL REACTION THAT INVOLVES LOSS AND GAIN OF ELECTRONS.

WHAT KIND OF ELEMENTS ARE INVOLVED IN IONIC REACTIONS?

WHAT KIND OF ELEMENTS ARE INVOLVED IN IONIC REACTIONS?

METALS AND NONMETALS

WHAT ARE METALS?

WHAT ARE METALS?

METALS USUALLY HAVE THREE VALENCE ELECTRONS OR LESS.

THEIR VALENCE ELECTRONS ARE LOOSELY HELD – THEY LOSE THEM IN IONIC REACTIONS.

MOST ARE SOLID AT ROOM TEMPERATURE (ONE EXCEPTION, Hg).

THEY ARE GOOD CONDUCTORS OF HEAT AND ELECTRICITY.

THEY ARE MALLEABLE AND DUCTILE.

WHAT ARE NONMETALS?

WHAT ARE NONMETALS?

THEY HAVE 5 OR MORE VALENCE ELECTRONS.

THEY GAIN ELECTRONS IN IONIC REACTIONS.

MOST ARE BRITTLE SOLIDS OR GASES AT ROOM TEMPERATURE – ONE EXCEPTION (Br).

THEY ARE NOT GOOD CONDUCTORS OF HEAT OR ELECTRICITY.

WE WRITE FORMULAS FOR IONIC COMPOUNDS AS SIMPLE FORMULAS (THE SIMPLEST WHOLE NUMBER RATION OF ATOMS IN THE COMPOUND).

THIS IS BECAUSE IONIC COMPOUNDS USUALLY EXIST AS CRYSTALLINE SOLIDS AT ROOM TEMPERATURE.

WE WOULD WRITE THE FORMULA AS NaCl, AS THERE IS ONE Na+ FOR EVERY Cl-.

IN WRITING FORMULAS FOR IONIC COMPOUNDS, WE PUT THE METAL ION FIRST.

IN OUR FORMULA, CHARGES HAVE TO BALANCE. THIS MEANS THAT YOU HAVE TO HAVE THE SAME NUMBER OF POSITIVE CHARGES AS NEGATIVE CHARGES.

YOU START OUT WITH NEUTRAL ATOMS, SO AFTER THE REACTION, THE RESULTING COMPOUND STILL HAS TO BE NEUTRAL.

QUICK NOTE: HOW DO YOU KNOW THE CHARGE AN ION WILL HAVE?

1) LOOK AT THE GROUP NUMBER AND DETERMINE HOW MANY VALENCE ELECTRONS AN ATOM OF THE ELEMENT WILL HAVE.

2) METALS WILL LOSE ELECTRONS TO FORM POSITIVE IONS. METALS WILL LOSE THEIR VALENCE ELECTRONS.

3) NONMETALS WILL GAIN ELECTRONS TO FORM NEGATIVE IONS. NONMETALS WILL GAIN ENOUGH ELECTRONS TO SATISFY THE OCTET RULE.

SOME EXAMPLES:

SODIUM CHLORIDE – NaCl one Na+ and one Cl-

MAGNESIUM CHLORIDE – MgCl2 one Mg+2 and 2 Cl-

ALUMINUM CHLORIDE – AlCl3 one Al+3 and 3 Cl-

COPPER (II) SULFIDE = CuS one Cu+2 and one S-2

POTASSIUM NITRIDE – K3N 3 K+ and one N-3

HOW WOULD YOU WRITE THE FORMULA FOR ALUMINUM SULFIDE?

ALUMINUM HAS 3 VALENCE ELECTRONS. IT IS A METAL, SO IT WILL LOSE THOSE 3 ELECTRONS TO FORM Al+3.

SULFUR HAS 6 VALENCE ELECTRONS. IT WILL GAIN 2 TO GIVE IT 8. SO, IT WILL FORM S-2.

THE COMMON MULTIPLIER BETWEEN 3 AND 2 IS 6, WO YOUR FORMULA WILL BE

Al2S3 2 aluminum ions and 3 sulfide ions

SOME CHARACTERISTICS OF IONIC COMPOUNDS:

1. THEY ARE SOLIDS AT ROOM TEMPERATURE.

2. THEY ARE HELD TOGETHER BY ELECTROSTATIC FORCES OF ATTRACTION BETWEEN OPPOSITELY CHARGED IONS.

3. THEY HAVE VERY HIGH MELTING POINTS.

4. WHEN DISSOLVED IN WATER, THE SOLUTIONS ARE GOOD CONDUCTORS OF ELECTRICITY.

5. IF YOU APPLY ENOUGH FORCE, THE CRYSTALS WILL BREAK.