Elements and Ionic Compounds Unit II: Intro to Formulas LPChem1415

Elements andIonic Compounds

Unit II: Intro to Formulas

A. Element OR Compound?

Elements:Formulas only contain ONE symbol

Which means only ONE capital letter.Names are only ONE word long.

Compounds:Formulas contain two or more symbols.

Which means more than one capital letter.

Names are TWO words long.LPChem1415

Elements: A Review

We already learned that:Most element formulas consist of the

element symbol and nothing more.(Al, Cu, Ne, Au, etc.)

Seven elements are “diatomic” and always pair up in the elemental state:

(H2, N2, O2, F2, Cl2, Br2, I2)Elements go by their own names

But sometimes Carbon is sneaky.LPChem1415

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Compounds

There are different types of chemical compound. For this unit, we are only learning IONIC compounds:

Ionic compounds form by transfer of valence electrons.Valence electrons are the

outermost electrons in an atom.

This atom has lots of electrons.

But only ONE in its VALENCE.

The periodic table

The table is organized so similar

elements are together.

Similar properties are usually due to

similar # of valence electrons.

Groups of similar elements have special names:

# valence electrons

increases, left to right:

12 345678

Sodium has 1 valence electron

Chlorine has 7 valence electrons

12 345678

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Lewis Dot Structures

Show ONLY valence electrons

Each electron is shown as a dot.Electrons come in pairs– top, bottom, left,

& right of symbol.

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Valence Electrons & Stability

12 345678

Eight valence electrons = a “full octet”

Atoms with a full octet are the most stable

This is why the noble gases are “noble”

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All other elements work to achieve a

“full octet” by gaining, losing, or

sharing electrons:

Atoms are like onions– the electrons come in layers.

The sodium now has zero electrons in the diagram, but there was

already a full octet in the next lower layer, so it is stable now.

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Gaining or losing electrons gives the

atom a charge.

Charged particles are called IONS.If one atom loses electrons, another must gain

them.

Even tiny electrons are matter, and can’t be

created or destroyed!

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An atom that loses electrons becomes

positively charged.

This is a cation.

(Subtracting a negative

makes a positive!)

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Cations are Positive

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An atom that gains electrons becomes

negatively charged.

This is an anion.Note: the name changes

to the “–ide” form when it

becomes negative!

Barium is in column 2 and has 2

valence electrons

Sulfur is in column 16 and has 6

valence electrons

1 2 3 4 5 6 7 8

To get full octets:

Barium must lose TWO electrons

Sulfur must gain TWO electrons

Key Point: Ion charge is based on how

many electrons must be gained or lost to

get a full octet.

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Main Group Ion Charges

1+

2+ 3+ 4± 3- 2- 1-

0

Form because opposite charged ions attract each other.

Ionic Compounds

Cations and anions arrange themselves in

a “crystal lattice.”

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Ionic Crystals

A “crystal lattice”Is a 3-D grid of ions– the

general structure of ionic compounds

Is hard to melt

due to attraction

between anions

and cations

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C. Ionic Nomenclature

Ionic Names: Cations

Write the name of the cation first.

Stock System: Use Roman numerals to show the cation’s charge if more than one is possible.

D-block (transition metals)

Poor metals

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How do you know the Roman numeral? Math! (The overall charge must equal zero.)

oFeCl2 • Cl gets a charge of: 1- (because it is in column 17)

• Fe must have a charge of ____ to make the compound = 0

2+ oThis is Iron (II)

Chloride

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Fe2 S3

There are only two capital letters, so no polyatomic ion to worry about.

I look up S on the periodic table

oColumn 16:

o6 valence electrons, 2- charge

S

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Fe2 S3 = iron ( ? ) sulfide

Fe2 S3

2-

6-

( ) 3

= 06+

( )2 +3+

Iron (III) sulfide

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Fe2 (CO3)3 = iron ( ? ) carbonate

Fe2 (CO3)3 2-

6-

( ) 3

= 06+

( )2 +3+

Iron (III) carbonate

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Fe CO3 = iron ( ? ) carbonate

Fe CO3 2-

2-

( ) 1

= 02+

( )1 +2+

Iron (II) carbonate

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Ni2 CO3 = nickel ( ? ) carbonate

Ni2 CO3 2-

2-

( ) 1

= 02+

( )2 +1+

Nickel (I) carbonate

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Ionic Names: Cations

Roman numerals are NOT needed for:

Group 1 & 2

o(1+, 2+)

Ag, Zn, Al

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Monatomic anion names are the first syllable of the element name, then -ide.

(Chloride, oxide, phosphide, nitride, etc)

Polyatomic ions have special names. (Chart on the back of your periodic table.)

Do NOT change the ending of polyatomic ions.

Ionic Names: Anions

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Consider the following:Does it contain a polyatomic ion?o2 elements no; ending is “-ide”o3+ elements yes; ending is -ate -ite

Does it contain a Roman numeral?oCheck the table: is the metal NOT in Groups 1 or 2 (or Ag, Zn, Al)?

NO numerical prefixes!

Overview:

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NaBr

Na2CO3

FeCl3

sodium bromide

sodium carbonate

iron(III) chloride

Documents

Elements and Ionic Compounds Unit II: Intro to Formulas LPChem1415