CHEMICAL COMPOUNDSTopic 6

COMPOUNDS

What is a compound? A group of 2 or more elements It takes on properties different than those of the

separate elements that compose it

IONIC AND MOLECULAR COMPOUNDS

Ionic Compounds Are formed when atoms give/take electrons

Molecular Compounds Are formed when atoms share electrons

We’ll look at Ionic Compounds first

IONIC COMPOUNDS

PROPERTIES OF IONIC COMPOUNDS

Formed from metals and non-metals Forms ions in solutions Conducts electricity Solid at room temperature

HOW IONIC COMPOUNDS ARE FORMED

Once an atom give up electrons, it becomes positive

Once an atom takes electrons, it becomes negative

Na9p

Cl11p

9 e- 11 e-

REMEMBER… Positives and negatives attract Once Na becomes Na+ and Cl becomes Cl- , they are

attracted to each other

Na+ Cl-

9 p 11 p

8 e- 12 e-

Overall charge +1 -1

CHEMICAL FORMULAS

Chemical formula – uses symbols and numerals to represent the composition of a pure substance.

H2O

Symbol forthe element

hydrogen

Symbol forthe element

oxygen

The small number here

means 2 atoms of hydrogen

No small numberhere means 1

atom of oxygen

THEORY BEHIND CHEMICAL FORMULAS

CaCl21 ion Ca 2 ions Cl

each ion is +2 each atom is -1 1 x (+2) = (+2) 2 x (-1) = (-2)

(+2) (-2)

Overall charge on the compound = 0

HOW TO WRITE CHEMICAL FORMULAS WITHOUT ACTING IT OUT OR DOING MATH

If your periodic table has ion charges listed in the corner, look at the ion charge for each element.

Ca+2 and Cl-1

Ca Cl

To become… Ca1Cl2 CaCl2

The superscript should be written as a positive or a negative because the number it’s representing is a number of atoms, not a charge anymore.

WRITING CHEMICAL FORMULAS

Step Example1. Write the symbol of the metal, then the

non-metalCa Cl

2. Write the number of the charge of the metal as a subscript after the non-metal

CaCl2

3. Write the number of the charge of the non-metal as a subscript after the metal

Ca1Cl2

4. Simplify to lowest terms if applicable. Eliminate any 1s if applicable

Final Answer: CaCl2

Note: The superscript shouldn’t be written as a positive or a negative because the number it’s representing is a number of atoms, not a charge anymore.

Example: What is the chemical formula of the product of calcium and chlorine?

NAMING IONIC COMPOUNDS

1. The name includes both elements in the compound, with the name of the metal first.

2. The non-metal element is second. Its ending is changed to –ide.

Examples:Calcium chloride (instead of Calcium chlorine)

Magnesium flouride (instead of magnesium flourine)

Sodium iodide (instead of sodium iodine)

Zinc sulfide (instead of zinc sulfur)

POLYATOMIC IONS

Some ions form when certain atoms of elements combine. These ions are called polyatomic ions. (poly- means “many”).

Polyatomic ions are a group of atoms acting as one.

They combine with metals in the same way that a single atom does.

WRITING CHEMICAL FORMULAS WITH POLYATOMIC IONS

Chemical formulas are written almost the same as other ionic compounds.

Calcium and nitrate Ca+2 and NO3

-

CaNO3

Ca(NO3)2 why not just CaNO32?

Differences: Brackets must be written around the polyatomic ion to identify that it is acting as one atom

NAMING COMPOUNDS WITH POLYATOMIC IONS

Naming with a polyatomic ion is very similar to naming compounds between two elements …but easier

Write the name of the metal, then the name of the polyatomic ion. Do NOT change the ending of the polyatomic ion

Examples: Calcium carbonate, sodium nitrate

MULTIVALENT IONS

Some ions have the ability to give up different amounts of electrons which means that they have two possible charges.

Writing formulas with multivalent ions are done just as they were with an ion with only one charge.

Titanium + Oxygen = Ti2O3

NAMING COMPOUNDS WITH MULTIVALENT IONS

When writing names with a multivalent ion, you must indicate which version of the element you are using. (The first listed is always more common)

Example: Titanium and oxygen (elements) Ti+3 and O-2 (ions) Ti2O3 (chemical formula) Titanium (III) oxide (name)

JUST BE CAREFUL WHEN…

Your elements have even numbers of atoms and they have been simplified.

Example: TiO2 = Titanium (IV) oxide

Remember… Titanium (IV) oxide Ti+4 and O-2

Ti2O4 simplified to TiO2

PRACTICE TIME!

ANSWERS

Chemical Formula Chemical Name

1. NaCl Sodium chloride

2. BeO Beryllium oxide

3. K2S Potassium sulfide

4. LiF Lithium fluoride

5. CaBr2 Calcium bromide

6. AgI Silver iodide

7. PbCl2 Lead (II) chloride

8. MgO Magnesium oxide

9. BaI2 Barium iodide

10. LiBr Lithium bromide

ANSWERS

11.

MgCl2 Magnesium chloride

12.

CuO Copper (II) oxide

13.

K2S Potassium sulfide

14.

VBr5 Vanadium (V) bromide

15.

CsI Cesium iodide

16.

MnS2 Manganese (IV) sulfide

17.

MnS Manganese (II) sulfide

18.

AuI3 Gold (III) iodide

19.

Pt3P2 Platinum (II) phosphide

20.

Tl2O3 Thallium (III) oxide

MOLECULAR COMPOUNDS

DEFINITIONS Molecule

The smallest independent unit of a pure substance and is generally a cluster of atoms joined together.

Diatomic molecules Molecules made up of two atoms of the same element. These atoms can never be alone, if they aren’t bonded

with another element, they bond with another identical atom.

7+1 Rule: In the shape of a 7 + Hydrogen on the periodic table Nitrogen, Oxygen, Flourine

Chlorine Bromine

Iodine

They create N2, O2, F2, Cl2, Br2, I2, H2

PROPERTIES OF MOLECULAR COMPOUNDS Composed of two or more non-metals They can be solids, liquids or gases They tend to be insulators, or poor conductors The forces between the molecules are weak bonds They share electrons

HOW MOLECULAR COMPOUNDS ARE FORMED

Molecular compounds share electrons instead of transferring them. Oxygen has 6 valence electrons Hydrogen has 1 valence electron.

If Oxygen shares electrons with two atoms of hydrogen, oxygen can have 8 electrons and each hydrogen can have 2 electrons – full shells for both Example: Water

MOLECULAR COMPOUND EXAMPLES

Diatomic molecule

Diatomic molecule

NAMING MOLECULAR FORMULAS

1. Write the name of the first element.2. Change the name of the second element to end with the suffix

“ide”3. When there is more than one atom in the formula, add a prefix to

indicate the number of atoms. Some are listed below. Exception: When the first element has only one atom, the prefix

mono is not used.

WRITING FORMULAS FOR MOLECULAR COMPOUNDS

Unless you’re given the name, writing formulas for molecular compounds are tricky because they don’t deal with charges.

Why don’t they deal with charges? Because there are no ions (nothing has given or

taken electrons).

We won’t deal with writing formulas without the names. Just make sure you can convert the name to the chemical formula and back again.

DRAWING MOLECULAR COMPOUNDS

Glucose Cocaine Propane

Ethanol Caffeine Acetaminophen

HOWEVER…

All you’ll have to draw is something like this

NH3 H2 BrO2

H H – H

N Br

H H O O

PRACTICE TIME!!!

ORGANIZING BONDINGMonovalent Ionic

Multivalent Ionic

Polytomic Ionic

Molecular

Dealing with Electrons

Give/take Give/take Give/take Share

Chemical Formulas

Cross charges into subscripts

Cross charges into subscripts

Cross charges into subscripts – put brackets around polytomic ion

Write the subscript that corresponds to the prefix.

Naming Metal + nonmetal with –ide ending

Metal + Roman numeral indicating charge + nonmetal with –ide ending

Metal + polytomic ion name (no name change)

Turn the subscript number into a prefix name.

Example NaClSodium chloride

AuI3Gold (III) iodide

Au2(CO3)3

Gold (III) carbonate

F2ODifluorine monoxide