Forming Ionic Compounds

Adrena McDonald

Venture Alternative High School

Before We Begin

• Cut out the ions from your student worksheets.

• Have a glue stick ready to attach the ions to your compound worksheet.

• Now, let’s do the first few together.

Cl-1

Cl-1

Cl-1

B+3

1. Boron (B+3) + Chlorine (Cl-1)

1 boron atom for every 3 chlorine atoms

1. BCl3

boron chloride

BCl3

2. Magnesium (Mg+2) + Chlorine (Cl-1)

1 magnesium atom for every 2 chlorine atoms

2. MgCl2

magnesium chloride

MgCl2

Mg+2Cl-1

Cl-1

3. Sodium (Na+1) + Chlorine (Cl-1)

1 sodium atom for every 1 chlorine atom

3. NaCl

sodium chloride

NaCl

Na+1 Cl-1

4. Calcium (Ca+2) + Sulfur (S-2)

1 calcium atom for every 1 sulfur atom

4. CaS

calcium sulfide

CaS

Ca+2S-2

5. Aluminum (Al+3) + Nitrogen (N-3)

1 aluminum atom for every 1 nitrogen atom

5. AlN

aluminum nitride

AlN

Al+3

N-3

Now, it’s your turn.

Do the remaining questions on your own.

6. Calcium (Ca+2) + Bromine (Br-1)

1 calcium atom for every 2 bromine atoms

6. CaBr2

calcium bromide

CaBr2

Ca+2Br-1

Br-1

7. Potassium (K+1) + Chlorine (Cl-1)

1 potassium atom for every 1 chlorine atom

7. KCl

potassium chloride

KCl

K+1 Cl-1

O-2

O-2

O-2

B+3

B+3

8. Boron (B+3) + Oxygen (O-2)

2 boron atoms for every 3 oxygen atoms

8. B2O3

boron oxide

B2O3

9. Magnesium (Mg+2) + Oxygen (O-2)

1 magnesium atom for every 1 oxygen atom

9. MgO

magnesium oxide

MgO

Mg+2O-2

10. Aluminum (Al+3) + Fluorine (F-1)

1 aluminum atom for every 3 fluoride atoms

10. AlF3

aluminum fluoride

AlF3

F-1

F-1

F-1

Al+3

11. Potassium (K+1) + Iodine (I-1)

1 potassium atom for every 1 iodine atom

11. KI

potassium iodide

KI

K+1 I-1

12. Sodium (Na+1) + Nitrogen (N-3)

3 sodium atoms for every 1 nitrogen atom

12. Na3N

sodium nitride

Na3N

Na+1

N-3

Na+1

Na+1

13. Potassium (K+1) + Bromine (Br-1)

1 potassium atom for every 1 bromine atom

13. KBr

potassium bromide

KBr

K+1 Br-1

14. Lithium (Li+1) + Fluorine (F-1)

1 lithium atom for every 1 fluorine atom

14. LiF

lithium fluoride

LiF

Li+1 F-1

15. Magnesium (Mg+2) + Nitrogen (N-3)

3 magnesium atoms for every 2 nitrogen atoms

15. Mg3N2

magnesium nitride

Mg3N2

Mg+2

Mg+2

N-3

N-3

Mg+2

Questions?

B+3 Cl-1

B Cl1 3

• Boron (B+3) + Chlorine (Cl-1) boron chloride

You can also determine the formula for a compound using the “criss-cross” method. Take the numbers from the ions’ superscripts and cross them to become the subscripts in the compound. Look at question #1.

13

BCl3

Mg+2 N-32 3

Mg N3 2

• Magnesium (Mg2+) + Nitrogen (N-3) Magnesium nitride

• Look at #15 to practice the “criss-cross” method again.

Mg3N2

K+1 (SO4)-21 2

K (SO4)

• Potassium (K+1) + Sulfate (SO4-2) potassium sulfate

• This also works for polyatomic ions.

K2SO4

Parentheses are not used unless a subscript is needed after the polyatomic ion, as you will see in the next example.

Al+3 (SO4)-23 2

Al (SO4)

• Aluminum (Al+3) + Sulfate (SO4-2) aluminum sulfate

• Use parentheses to indicate that more than one of the same polyatomic ion is included in the compound.

Al2(SO4)3

• If the superscript charges add to zero, DO NOT criss-cross. All compounds have a zero charge, so it takes one of each ion to make the compound:

• Ca+2 + O-2 CaO

• B+3 + N-3 BN

(+2 and -2 = 0)

(+3 and -3 = 0)

Released TAKS Question

calcium (Ca+2) + chlorine (Cl-1) calcium chloride

The chemical formula for calcium chloride is ---

A) Ca2Cl

B) CaCl

C) CaCl2D) Ca2Cl3

Ca+2 Cl-1

Ca Cl1 2

12

CaCl2

Released TAKS Question

According to this information, what is the chemical formula for aluminum sulfate?

A) AlSO4

B) Al2(SO4)3

C) Al3(SO4)2

D) Al6SO4

Al3+ SO42-

Al+3 (SO4)-23 2

Al (SO4)

Al2(SO4)3

Questions?

• Good job!!!• Don’t forget to put your name on your

paper before you turn it in.

K+

1B+3

Ca+2

Ca+2

Li+1

Mg+2

Na+1

K+1

Ca+2

Na+1

Cl-1Cl-1Cl-1F-1

F-1

F-1

Br-1

O-2

O-2

O-2

S-2

Mg+2

Mg+2

Al+3

Na+1

K+1

Al+3

B+3

I-1B

r-1B

r-1

Mg

+2

N-3

N-3

P-3

P-3

S-2

Cl-1

1. Boron (B+3) + Chlorine (Cl-1) boron chloride ____________

2. Magnesium (Mg+2) + Chlorine (Cl-1) magnesium chloride ____________

3. Sodium (Na+1) + Chlorine (Cl-1) sodium chloride ____________

4. Calcium (Ca+2) + Sulfur (S-2) calcium sulfide ____________

5. Aluminum (Al+3) + Nitrogen (N-3) aluminum nitride ____________

6. Calcium (Ca+2) + Bromine (Br-1) calcium bromide ____________

7. Potassium (K+1) + Chlorine (Cl-1) potassium chloride ____________

8. Boron (B+3) + Oxygen (O-2) boron oxide ____________

9. Magnesium (Mg+2) + Oxygen (O-2) magnesium oxide ____________

10.Aluminum (Al+3) + Fluorine (F-1) aluminum fluoride ____________

11. Potassium (K+1) + Iodine (I-1) potassium iodide ____________

12.Sodium (Na+1) + Nitrogen (N-3) sodium nitride ____________

13.Potassium (K+1) + Bromine (Br-1) potassium bromide ____________

14.Lithium (Li+1) + Fluorine (F-1) lithium fluoride ____________

15.Magnesium (Mg+2) + Nitrogen (N-3) magnesium nitride ____________

Write the chemical formula for the following compounds. Place the cutouts in the corresponding boxes on the following pages.

1. B+3 + Cl-1 2. Mg+2 + Cl-1

3. Na+1 + Cl-1 4. Ca+2 + S-2

5. Al+3 + N-3 6. Ca+2 + Br-1

7. K+1 + Cl-1 8. B+3 + O-2

9. Mg+2 + O-2 10. Al+3 + F-1

11. K+1 + I-1 12. Na+1 + N-3

13. K+1 + Br-1 14. Li+1 + F-1

15. Mg+2 + N-3

1. Boron (B+3) + Chlorine (Cl-1) boron chloride _____BCl3 _____

2. Magnesium (Mg+2) + Chlorine (Cl-1) magnesium chloride ____ MgCl2 _____

3. Sodium (Na+1) + Chlorine (Cl-1) sodium chloride _____NaCl _____

4. Calcium (Ca+2) + Sulfur (S-2) calcium sulfide _____CaS _____

5. Aluminum (Al+3) + Nitrogen (N-3) aluminum nitride _____AlN ______

6. Calcium (Ca+2) + Bromine (Br-1) calcium bromide ____CaBr2 ______

7. Potassium (K+1) + Chlorine (Cl-1) potassium chloride _____KCl _______

8. Boron (B+3) + Oxygen (O-2) boron oxide ____ B2O3 _______

9. Magnesium (Mg+2) + Oxygen (O-2) magnesium oxide _____MgO ______

10.Aluminum (Al+3) + Fluorine (F-1) aluminum fluoride _____AlF3 ______

11. Potassium (K+1) + Iodine (I-1) potassium iodide _____ KI_______

12.Sodium (Na+1) + Nitrogen (N-3) sodium nitride ____Na3N ______

13.Potassium (K+1) + Bromine (Br-1) potassium bromide _____KBr _______

14.Lithium (Li+1) + Fluorine (F-1) lithium fluoride _____ LiF ________

15.Magnesium (Mg+2) + Nitrogen (N-3) magnesium nitride ____Mg3N2 ______

Key

Notes to Teacher• If you want to have the students cut out the ions themselves, they will

need two copies of the ion sheet to complete the assignment.• In order to save time you may want to try having the students cut out

the ions as homework.• If you are a paper-saving type, you can make class sets of ions (just

one sheet per student since they can reuse ions) and not have the students actually paste them on the answer sheets. Instead, you can:– Have a class set of ions premade and laminated. Put them in

ziploc bags to keep them separate. You can also laminate a class set of answer sheets if you want the students to have a reusable place to work out their solutions.

– Print the ion pages on magnetic paper and cover it with adhesive laminate prior to cutting out the pieces. Then place these sets in ziploc bags. Students can rearrange the ions on whiteboards or cheap cookie tins (which can be purchased at most dollar stores) before writing down their answers.