Science 10 Unit 2

YAY, WE’RE DONE 4.1 !

• GREAT JOB: Now you understand how to draw models of ionic and covalent compounds!! (Right? )

• WHAT’S NEXT??

• Now you will learn how to properly write the chemical formula of ionic and covalent compounds

(e.g., H20 is the chemical formula for water)

• You will also learn how to properly name ionic and covalent compounds (e.g., magnesium phosphide is the name of the ionic compound formed from magnesium and phosphorus)

• Writing the name and chemical formula for a compound is done differently if it’s an ionic or covalent compound.

(Can’t chemistry ever be simple?)

• Today, we will focus on the method for ionic compounds;

next class, we’ll cover the method for covalent compounds.

E.g.: What is the chemical formula for calcium oxide?• “oxide” means oxygen, so there are calcium and oxygen in the compound• look up the ions that calcium and oxygen typically form in an ionic

compound on your Periodic Table …

• Notice the charges balance if there is one Ca2+ ion and one O2– ion, so the chemical formula is written as:

Calcium becomes Ca2+ Oxygen becomes O2-

Ca1O1(actually, the subscript 1 is

never written…)

SKILL 1: Writing the chemical formula for an ionic compound

KEY IDEA: In an ionic compound, the positive charges must balance the negative charges.

CaOWrong!! Right!

Magnesium is Mg2+ Phosphorous is P3-

Lowest common multiple of 2 and 3 is 6

3 Mg2+ ions needed and 2 P3– ions needed to balance charges

Mg3P2

But what if one ion of each do not balance each other out?

• “phosphide” means phosphorus, so look up the ions that magnesium and phosphorus form…

• Notice one ion of each will NOT balance the charges!• Can you figure out how many Mg ions and P ions will be needed to

exactly balance each other out??

E.g.: What is the formula for magnesium phosphide?

And the chemical formula is…

YOU TRY: What is the formula for aluminum fluoride?

Aluminum is Al3+ Fluorine is F -

To balance charges, 3 Fluoride ions are needed for every 1 Aluminum ion…

AlF3

** Notice that the metal is always written first!!

Mg2+ P3-

Mg2+ P3-

Mg2+

6+ 6-

Mg3P2

The crystal lattice formed has 2 phosphide ions for every 3 magnesium ions, so charges are balanced!

1. Write both symbols (+ion first) with ion charge

2. Criss-cross the charges and write them as subscripts

3. Reduce if possible

Pb S4+ 2-

Pb S42

Pb1S2

(Useful, but unnecessary if you understand that + and - charges must balance!)

Lead sulphide

4. Remember that the subscript 1 is never written

PbS2

In the shortcut example, you may have been confused because lead has more than one combining capacity

(i.e., more than one ion charge listed on the Periodic Table)

Fe O2+ 2-

FeO

e.g. Cu2+ Cu1+ Pb4+ Pb2+

If this is the case, the name of the compound will always include a roman numeral to tell you which combining capacity to use…

Iron II oxidee.g. Iron III oxide

Fe O3+ 2-

Fe2O3

1+ I 2+ II 3+ III 4+ IV

5+ V 6+ VI 7+ VII

So Iron & Oxygen

can form two

different compounds

together!

PRACTICE!

Try Practice Problems:

p.188 #1 a-f & #2 a-f

p.190 #1 a-f(It says in the text where to find the

answers, so PLEASE check your work as you go and get help if needed!!)

1. Write the name of the metal first.

2. Write the name of the non-metal second, and change the ending to “-ide”

3. ONLY IF THE METAL HAS 2 OR MORE ION CHARGES, include a roman numeral to indicate which one it is.

e.g. NaCl

MgF2

CuCl2

Sodium chloride

Magnesium fluoride

copper has 2 ions: Cu 1+

Cu 2+

which one is it?

SKILL 2: Writing the name of an ionic compound

KEY IDEA: Metal + Non-metal (with “-ide” ending)

To find out which copper ion it is, look at the charge on the anion and balance the charges in reverse.

(Can also be written as copper (II) chloride)

Cu Cl2+ 1-

CuCl2

Therefore it is copper II chloride

from periodic table

Cl 1-

2-

Aluminum Sulphide

Gold has 2 ions: Au3+

Au+

Aluminum is NOT multivalent, so we don’t have to worry about Roman numerals

YOU TRY: What is the name for Al2S3?

YOU TRY: What is the name for Au3N?

Gold is multivalent, so we must worry about Roman numerals!!

Nitrogen is: N 3-

To balance charges, which Au ion must it be?

Gold (I) Nitride

PRACTICE!

Try Practice Problems:

• p.187 #1 a-f• p.191 #1 a-j (the multivalent type!)

Again, check your answers as you go!

e.g. SO4-2 Sulphate ion -2

OH-1 Hydroxide ion -1

PO4-3 Phosphate ion -3

KEY IDEA: When you see a polyatomic ion, treat it as if it is just one atom and follow the rules as usual.

e.g. K+1 -3

K3PO4

Potassium phosphate

Important note: Don’t change the endings of polyatomic ions!

Ion Charge

PO4

ACK! Can you handle ONE MORE complication?A polyatomic ion is a group of atoms that together act as an ion.(Think about what that means.)The group of atoms is given a name.

Good news: All the polyatomic ions you need to know, and their charges, are included in your Data Pages! Have a look! Can you find the 3 examples?

Formula:

Name:

Aluminum sulphate

Copper (II) sulphate

Al SO4+3 -2 Al2(SO4)3

Cu+2CuSO4

Brackets are necessary around the SO4 to indicate 3 sulphate ions, not 43 oxygen atoms!

SO4-2

Don’t forget the roman numeral since copper has more than one combining capacity

YOU TRY: If the ions below form an ionic bond, write the formula and name.

formula

formula name

name

PRACTICE!

Try Practice Problems:

p.193 #1 a-e & #2 a-e (Check answers!!)

HomeworkIf you feel shaky on this stuff, give yourself some more time to

pick it up. You can do it! I suggest you read through text p.184-191. Each time you hit a set of “Practice Problems,” try doing some more of them and checking your answers. I suggest this for everyone but especially those feeling a little overwhelmed.

Once you feel comfortable with the material, then:

1. Read and highlight workbook p.65-66

2. Complete workbook p.68-69 Be ready to have the workbook marked next class along with the

workbook from last day. Don’t let yourself get behind here. We’re plowing forward next class and

will be writing a test before the break!!