Introduction to Chemical Compounds Why do elements combine?

Introduction to Chemical Compounds

Why do elements combine?

So Far We’ve Learned:

That atoms are made up of Protons, Neutrons, and Electrons

The identity of an atom is determined by the number of protons in the nucleus

BUT, compounds form due to the interactions between electrons

How are Electrons Involved?

•I. Either Shared (Covalent) or Transferred (Ionic)

Using the Periodic Table, we can predict an element’s electron behavior.

A (-) charge = gained electrons

A (+) charge = lost electrons

General Rules (ionic):

Metals will ALWAYS form + ions (cations)

Non-metals will ALWAYS form – ions (anions)

Chemical compounds form from the interaction between oppositely charged ions:

• Na+1 + Cl-1 -------> NaCl

• sodium ion + chloride ion ----> sodium chloride

BIG IDEA:

Every element is trying to rearrange its electrons (by gaining or losing them) in order to “look like” a noble gas element.

This is called achieving a “Noble Gas Configuration. (Full outer electron shell)

Predicting Oxidation Number by Position

Identifying IonsName Common Ion (Na+1) Cation or Anion Anion “ide” name

Strontium      

Iodine      

Nitrogen      

Oxygen      

Lithium      

Magnesium      

Silver      

Zinc      

Iron (II)      

Phosphorous      

Sulfur      

Aluminum      

Fluorine      

Chlorine      

Potassium      

Bromine      

Cesium      

Francium      

Chromium (VI)      

When Ions Combine, the Compound MUST

be NeutralAll (+) charges must be cancelled by (-) charges

Need to combine ions in smallest proportion that will cancel charges.

Li and Cl

Mg and Cl

Al and Cl

Li and O

Mg and O

H and S

ANSWERS:LiCl (Li+1 + Cl-1)

MgCl2 (Mg+2 + 2Cl-1)

AlCl3 (Al+3 + 3Cl-1)

Li2O (2Li+1 + O-2)

MgO (Mg+2 + O-2)

H2S (2H+1 + S-2)

Anatomy of a Chemical Formula

1.Symbols for the elements in the compound

2.Numbers called subscripts that indicate how many atoms of an element are present:

• AlCl3 = 1 Al and 3 Cl

• This should makes sense because Al has a +3 charge and Cl has a -1 charge

3.The subscript is ONLY associated with the element symbol to the immediate left.

TRY THESE:

Roman numerals indicate value of positive charge

Polyatomic Ions

“Poly-” means many

Polyatomic ions are charged particles that consist of more than one atom

These ions can combine just like ions formed from single elements

Common Polyatomic Ions

Just One Catch!

If more than one polyatomic ion is needed, the formula for the compound will need to have parenthesis around this ion

Example: Mg+2 + PO4-3 ----> Mg3(PO4)2

Polyatomic Ions May be Used Like Other

IonsJust like Sodium (Na+) can combine with chloride (Cl-1), to make NaCl

A polyatomic ion called ammonium (NH4

+1) can combine with chloride (Cl-1) to make NH4Cl

The N and 4 H’s that make up NH4 , collectively loose 1 electron to become NH4

+1

Ion Cut-Out Lab

Goal: Make Compounds Using Paper Models of

Ions

KBr Postassium Bromide

K3PO4 Potassium Phosphate

Goal for today: Complete as much of chartas possible. Do NOT Name compounds.

Naming Ionic Compounds

1.Determine the ions that make up the compound. (Use Periodic Table or “Common Ions Chart”)

2.Write the name of the POSITIVE ion first

3.Write the name of the NEGATIVE ion second. (Sometimes the name of this ion will change slightly)

Negative Ion Names

Name endingchanges to

“-ide”

Non-metal elements in columns 14-17 will form negative ions with names ending in “-

ide”.

Examples:

•Chlorine becomes chloride

•Fluorine becomes fluoride

•Oxygen becomes oxide

•Phosphorous becomes phosphide

•Nitrogen becomes nitride

If polyatomic ions are used...

Naming is easy!

Just put the names of the ions together (positive first, negative second)

No Name changes are needed

• Example:

• Mg3(PO4)2 is named Magnesium phosphate

Positive ion Negative ion

Transition Metals

If the positive ion is a transition metal,the name of the compound MUST

includea Roman Numeral!

Here’s an example: There are two “iron chlorides”:

FeCl2 is iron (II) chlorideFeCl3 is iron (III)

chloride

The Roman Numeral indicates the charge of the metal ion