Chapter 9

Chemical Names & Formulas

Ionic vs. Covalent

• Ionic bonds form between a metal cation and a non-metal anion.

• There is a full transfer of electrons.

• A covalent (molecular) bond occurs between two non-metals.

• Electrons are shared.

IONS• Ion – an atom or group of atoms with a

charge• Cation – Ion with a positive charge• Anion – Ion with a negative charge• Monatomic ion – consist of a single

atom• Polyatomic ion – consists of more than

one type of atom

CATIONS• Elements in group 1, 2, and 3 lose

electrons and form cations.• Why is sodium + 1 and magnesium

is + 2?(hint: drawing a diagram may help)

• Atoms try to achieve noble gas configuration with their electrons.

• Cations have the same name as the element from which they form

• Elements in group 15, 16, & 17 gain electrons to form anions

• How many electrons will chlorine gain?what will its charge be?

• Monatomic anions have the ending -ide• The remaining elements in group 4 & 14

don’t normally form ions. Why?

ANIONS

Ions of Transition Metals

• Transition metal cations may have more than one possible charge.

• Iron for example can have a +2 or a +3 oxidation state.

• A roman numeral in parantheses shows the oxidation state of the metal.– e.g. Iron (III), Iron (II)

…continued

•A few transition metals have only one oxidation state (Ag+,

Cd2+, Zn2+) and do not need a Roman Numeral.

•Can you find any other transition metals that have only one oxidation state?

Writing Formulas• Formulas need to have an overall charge of

zero.

• Write the symbol of the cation first then the anion. Then, add whatever subscripts are needed to balance the charges.

Example:

Potassium chloride is composed of

K+ and Cl -

The formula is KCl

…CONTINUED

• The formula for lithium oxide is Li2O

• Each lithium has one positive charge, so two lithium atoms are needed to balance the –2 charge on oxygen.

• The formula for aluminum oxide is Al2O3

• How do we come up with this formula?

The Crisscross Method

If the charges do not already add to zero, the numerical value of the charge can be crossed down to become the subscript of the other ion.

Al3+ O2-

Polyatomic Atoms

Composed of more than one atom, most of these ions end in –ite or -ate

Formulas With Polyatomics

• Write the symbols for the cation followed by the formula for the polyatomic anion, and balance the charges.

• If you need more than one polyatomic ion, (parentheses are necessary)

• Calcium nitrate is written Ca(NO3) 2

PRACTICE

Write the correct formula for the following:

- Lithium fluoride

- Magnesium chloride

- Aluminum sulfide

- Calcium phosphate

- Potassium chlorite

Things to keep in mind…

• There are three common polyatomic ions that end in –ide

• Hydroxide

• Peroxide

• Cyanide

• You may run into 3 names together, e.g. sodium hydrogen carbonate.

Naming Molecular Compounds

• Molecular compounds are covalently bonded and are composed of two non-metals.

• What are the names for CO2 and CO?– Carbon dioxide & carbon monoxide.

• Where do we find each of these gases?

PREFIXES• Prefixes tell us how many atoms of an element are present

in each molecule of a compound.

1 2 3 4 5 6 7 8 9 10Mono Di Tri Tetra Penta Hexa Hepta Octa Nona Deca

• Omit the prefix mono- when the formula contains only one atom of the first element in the name.

• The ending of the second element is –ide

• The vowel at the end of a prefix is dropped if the name of the elements begins with a vowel.

Writing Formulas for Molecular Compounds

• The prefix tells you the subscript of each element in the formula.

• Silicon carbide has no prefixes and has the formula SiC.

• Dinitrogen tetroxide is N204

ACID• An acid contains one or more hydrogen

atoms and produces H+ ions when dissolved in water.

Formic Acid Hydrofluoric Acid

Naming Acids

• Formulas are generally in the form HnX, where X is an anion.

• The name system depends on the name of the anion, suffix.

RULES

1) When the anion ends in –ide, the acid name begins with hydro – and ends in – ic (followed by the word acid) ex. HCl = hydrochloric acid

2) When the anion ends in –ite, the acid name ends

in – ous (followed by the word acid) ex. H2S03 = sulfurous acid.

3) When the anion ends in –ate, the acid name ends in – ic (followed by the word acid) ex. HN03 = nitric acid.

Naming Bases• Bases are named the same way as

other ionic compounds.

Ex. NaOH = sodium hydroxideAl(OH)3 = aluminum hydroxide