Unit 6:Writing and Naming Chemical FormulasCHEMISTRY I

2013-2014

Ions & The Octet Rule

Vocabulary

Ion – an atom or bonded group of atoms with a positive or negative charge

Anion – a negatively charged ion

Cation – a positively charged ion

Octet Rule – “atoms lose, gain, or share electrons in order to acquire the stable electron configuration of a noble gas”

Ion

An ion is an atom or group of atoms that has either a positive or negative charge

Atoms form ions by gaining or losing electrons

Atoms gain or lose electrons to become stable

An atom is stable when the valence shell is full

Cations – Positive Ions

Sodium loses one electron to become stable

Results in an ion that has a positive charge

Cations

The symbol “+” is written as a superscript to indicate that the sodium has a charge of 1+

Na+

Anions – Negative Ions

Chlorine gains one electron to become stable

Results in an ion with a negative charge

Anion

The symbol “-” is written as a superscript to indicate that the chlorine ion has a charge of 1-

Cl-

The Octet Rule

Both ions have a full valence shell containing the maximum number of electrons possible (8)

This new arrangement of valence electrons has less energy than the previous arrangement and is stable

Na+ Cl-

Noble Gases

A metal atom that has lost electrons (cation) and a nonmetal atom that has gained electrons (anion) will have the same number of electrons as its nearest noble gas.

Common Charges

Naming Ions

Cations: A metal that has lost electrons to become an ion has the same name as the element

Ca2+ = calcium ion

Anions: A nonmetal that has gained electrons to become an ion has the same name as the element but with the ending changed to –ide

S2- = sulfide ion

Nitrogen Nitride Phosphorous Phosphide

Oxygen Oxide Flourine Flouride

Roman Numerals for Multivents

Multivents – an element that can form an ion in more than one way

Naming: Always include the ion charge as Roman numerals in brackets

Cu+ copper (I) “copper one”

Cu2+ copper (II) “copper two”

Transition Metals to Know

Scandium column: always +3, no Roman numeral needed

F-block: always +3, no Roman numeral needed

Ag: always +1, no Roman numeral needed

Cd & Zn: always +2, no Roman numeral needed

Sn & Pb: either +2 or +4

Charges Oxidation Number

An oxidation number is the positive or negative charge of an ion

Element Oxidation #

Li +1

Be +2

O -2

F -1

Polyatomic Ions

Writing and Naming Ionic Compounds

Ionic Compounds

Cation + anion

Name the cation first (typically a metal) just as it appears on the periodic table

Na+ = Sodium

Ca+2 = Calcium

Ionic Compounds

Write the anion next (typically a nonmetal)

Change the ending to –ide

**If the anion is a polyatomic ion, the name stays the same**

Practice

NaCl Sodium Chloride

AlCl3 Aluminum Chloride

Na2O Sodium Oxide

Al2O3 Aluminum Oxide

How to determine the Oxidation Number of Transition Metals

Identify the metal as a Transition with multiple oxidation numbers (ex. Fe)

Uncross the “criss-cross”

If nothing to uncross, identify the charge of the anion. The charges have been simplified

Transition metals will be the same just +

Fe2O3

+3 -2

FeS+2 -2

Iron (III) Oxide

Iron (II) Sulfide

Practice

CuO

Name: Copper (II) Oxide

Writing Ionic Formula

Identify the ions and their charges

Criss-Cross the charges The sum of the

oxidation numbers must equal zero, so by writing the subscripts we are able to balance the charge

Example: Calcium Chloride

Ions: Ca+2 and Cl-1

+2 -1

Ca Cl

Formula = CaCl2

(Don’t write 1’s)

Practice

Magnesium Oxide

Copper (I) Phosphide

Mg2O2

**Simplify to MgO

Cu3P

Polyatomic Ions

You can’t change the subscripts in Polyatomic Ions

Put the Polyatomic Ion in brackets and place the subscripts outside those

Calcium Phosphate

Ca+2 PO43-

Ca3(PO4)2

Naming Covalent Compounds

What’s the difference between covalent and ionic?

Ionic compounds have a metal and a nonmetal, a cation and an anion

Covalent compounds are called molecules They are made from elements that are similar in

electronegativity

Covalent Naming uses Prefixes

1.Mono

2.Di

3.Tri

4.Tetra

5.Penta

6.Hexa

7.Hepta

8.Octa

9.Nona

10.deca

Rules

If you have more than one atom of that element in the compound, you will need a prefix before it’s name.

Always put a prefix before the name of the second element

Change the ending of the second element to -ide

P2O5

Diphosphorous pentoxide

CO

Carbon monoxide

Practice

OF2

SO2

SO3

N2O5

N2O4

H2O

Oxygen diflourideSulfur dioxideSulfur trioxideDinitrogen pentoxideDinitrogen tetroxideDihydrogen monoxide

http://www.lhup.edu/~dsimanek/dhmo.htm

Names and Formulas of Common Acids and Bases

Naming Acids

Acids are almost always compounds made from hydrogen and an anion

Hydrogen + Halogen = hydro________ic acid HCl = hydrochloric acid

Hydrogen + Polyatomic ion –ate = _______ic acid HNO3 = nitric acid

Hydrogen + Polyatomic ion –ite = _______ous acid H2SO3= sulfurous acid

Naming Bases

Bases are almost always compounds made from hydroxide (HO-) and a cation

Cation + Hydroxide

Mg(OH)2 = Magnesium Hydroxide

LiOH = Lithium Hydroxide

Practice

Hydroiodic acid HBr H2CO3

Lead (II) Hydroxide

Sn(OH)4

Zn(OH)2

HI Hydrobromic

Acid Carbonic Acid

Pb(OH)2

Stannic Hydroxide

Zinc Hydroxide

Empirical and Molecular Formulas

Empirical Formula

The formula that gives the simplest whole number ration of atoms in a compound

Molecular Formula: C6H12O6

Empirical Formula: CH2O

What is the empirical formula of…?

C6H12O6

Fe3O2

C6H10O4

CH2O

Fe3O2

C3H5O2