Chemical Names & Formulas Chapter 9

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

ANIONS 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?

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 10 Mono 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 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 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 hydroxide Al(OH)3 = aluminum hydroxide