MondayNovember 12, 2012

(WS - Building and Naming Ionic Compounds)

Bell RingerMonday, 11-12-12

Write the formulas for the chemical compounds that are formed when the

following atoms bond:sodium and chlorine

NaCl

magnesium and bromine

MgBr2

calcium and oxygen CaO

aluminum and sulfur Al2S3

Announcements

Assignment Currently Open

Summative or Formative? Date Issued Date Due Date Into

GradeSpeed Final Day

QUIZ 9 S6 10/26 10/26 11/16

QUIZ 10 S7 11/2 11/2 11/16

WS – Covalent Bonding F14 11/7 11/16 11/16

QUIZ 11 S1 11/9 11/9 11/30

Chemical Compound Formation and Naming

A chemical formula indicates

the types of atoms and relative

number of each type of atom in a

chemical compound.

Chemical Formulas

Chemical FormulasFor an ionic compound, the chemical

formula reveals the ratio of ions of each element contained in the ionic matrix.

Al2O3In the ionic compound aluminum oxide, there are 2 ions of aluminum for every

three ions of oxygen in the ionic matrix.

Monoatomic Ions•Ions are created when a neutral atom

loses or gains electrons in the process of becoming stable.

•The atom no longer has equal numbers of protons (+) and electrons (-).

•Monoatomic ions (meaning “one atom”) are ions formed from a single atom.

• H+ Ca2+ Cl- O2-

Polyatomic Ions•Polyatomic ions (meaning

“more than one atom”) are ions formed from multiple atoms

bonded into a group.

• NH4+ Hg2

2+ OH- SO42-

• Notice that the number 1 is not shown.

Chemical FormulasFor an ionic compound made with one or more

polyatomic ions, the chemical formula still reveals the ratio of ions, whether they are monoatomic

ions or polyatomic ions.

Al2(SO4)3In the ionic compound aluminum sulfate, there are 2 ions of aluminum for every three ions of sulfate in the ionic matrix.

Cations and Anions• When atoms lose electrons, they now

have more protons (+) than electrons (-), and take on the + charge of the extra

protons. Positively charged ions are called “cations.”

•K+•NH4+

•Br-

•OH-

•When atoms gain electrons, they now have fewer protons (+) than electrons

(-), and take on the - charge of the extra electrons. Negatively charged

ions are called “anions.”

Oxidation NumbersOxidation numbers (the

green numbers above the main-block groups on the larger Periodic Table on the right) indicate the

charge on that atom’s ion after it has lost or gained electrons in the process of

becoming stable.

Na+

Mg2+

Al3+

C4+/-

Mg2+

N3-

O2-

F-

Oxidation NumbersOxidation numbers can be used to determine the ratio in which atoms

will bond to one another when forming chemical compounds.

This procedure is illustrated on the next slide.

“Crossing” oxidation numbers is a method of balancing the charges

between ions in an ionic compound.

For example:If an aluminum ion is bonding

with an oxygen ion:Al3+ + O2-

Al2O3

Crossing Oxidation Numbers

Notice that you do not cross the + and – charge signs, only the numbers of the

charges.

It is also important to remember that the positively-charged cation is always listed first in the chemical formula, followed by the negatively-

charged anion.

Crossing Oxidation Numbers

Therefore: Na+Cl-Never: Cl-Na+

Oxidation NumbersIn general, follow this system for determining an

elements oxidation number:

Group 1 = 1+ (+)Group 2 = 2+

Group 13 = 3+

Group 14 = 4+/-

Group 15 = 3-

Group 16 = 2-

Group 17 = 1- (-)Group 18 = 0

Since the d-block Transition Metals

(Groups 3-12) have variable

oxidation states, their oxidation

numbers will be listed as a Roman

numeral.Ex) Fe (III) = Fe3+

Binary Ionic CompoundsBinary ionic compounds are

compounds composed of two different elements.

In a binary ionic compound, the total numbers of positive and negative

charges must be equal.

ExampleMagnesium and bromine

combine to form magnesium bromide.

Mg2+ + Br- → MgBr2It takes 2 Br- anions, each with a 1- charge to balance Mg with

its 2+ charge!

Binary Ionic Compounds

Naming Monoatomic IonsMonoatomic cations are identified simply by

the element’s

name.

Naming Monoatomic IonsWhen

monoatomic anions are

bonded into compounds, their names are changed

to end in –ide

Naming Polyatomic IonsThe names of

polyatomic ions are never

changed as they are

bonded into compounds.

ExampleNa + NO3 æ NaNO3

sodium + nitrate æ sodium nitrate

Polyatomic Ions

Handout: Reference Sheet -

Polyatomic Ions

WorksheetBuilding and Naming

Ionic Compounds

MgF2

NaCl GaI3

SrO

HNO3

AlI3

H2SO4