Compounds

Advanced ChemistryPDA

Unit 3

I.) SUBSTANCESA.) SUBSTANCE- elements or compounds—they are composed of a uniform composition that does not vary from place to place.

1.) ELEMENTS-forms of matter that cannot be broken down 2.) COMPOUNDS-a substance that consists of two or more different elements.

Example. Lemonade is not a substance because not all samples of lemonade are identical. Lemonade contains more than one kind of matter and the relative amounts of each kind may differ in relation to their composition.

B.) CHEMICAL BOND-the force that holds atoms together in a compound

1.) IONIC BOND-involves the transfer of electrons from a metal to a nonmetal

2.) COVALENT BOND-consists of a pair of electrons shared between two nonmetals

Metals lose their valence electrons and nonmetals gain electrons to satisfy the octet

rule.Electron sharing satisfies the octet rule.

II.) OCTET RULE “The Rule of 8”A.) OCTET RULE states that atoms tend to combine in such a way that each has eight electrons in their valence shells identical to the noble gas nearest them in the periodic table.

1.) In order to satisfy the octet rule, atoms tend to gain, lose or share electrons to look like the noble gas that is nearest to them. The exception is Hydrogen. He is trying to achieve a noble gas configuration like Helium. Helium has only 2 valence electrons.

III.) IONS AND THE OCTET RULEA.) An ION is formed when an atom gain or loses an electron to satisfy the octet rule. The result is a charged particle.

1.) CATION (pronounced cat-ion) results from the loss of an electron giving a positively charged ion.2.) ANION (pronounced an-ion) results from the gain of an electron by an atom resulting in a negatively charged ion.

B.) Using group numbers to predict charge1.) For most of the s and p block elements, the charge on an ion can be predicted from the position of the element on the periodic table.

a.) The metals lose electrons to form cations.

b.) The nonmetals gain electrons to form anions.

2.) Some of the transition metals and metals in Group 4A have variable charges (more than one positive ion). See figure 1.

Figure 1. Common ions and their locations

IV.) Ionic Bond Formation

A.) An IONIC BOND forms by transfer of electron(s) from the metals to the nonmetals. The result is a formation of an ionic compound.

1.) Lewis structures, or electron dot formulas, are helpful in visualizing the formation of ionic compounds.2.) Using Lewis symbols, the formation of the ionic compound NaCl from the elements sodium and chlorine can be shown as follows:

Sodium needed to lose one electron for octet formation (to obtain the neon electron configuration), chlorine needed to gain one electron for octet formation (the argon

electron configuration). The electron transfer required 1:1 ratio of reacting atoms 1 Na to 1 Cl.

WORKED EXAMPLE 1Use the electron dot symbols to write the equation for the formation of the ionic compound formed between barium and iodine.Solution.Barium has to lose two electrons for octet formation (the xenon electron configuration).Iodine has to gain one electron for octet formation (the xenon electron configuration). The transfer of two electrons from barium requires the acceptance of those two electrons by two iodine atoms. The electron transfer requires 1:2 ratio of reacting atoms 1 Ba to 2 I.

PRACTICE 1Use the electron dot symbols to write the equation for the formation of the ionic compound formed between aluminum and fluorine.

A.) Formula Units1.) Ionic compounds

are electrically stable. Therefore, when writing formulas, the cations and anions must combine to produce a net charge of zero.

2.) Formulas for ionic compounds are called FORMULA UNITS.

V.) WRITING FORMULAS FOR IONIC COMPOUNDS

B.) The Cross Over method1.) When writing the formulas for ionic

compounds, follow the following steps to always achieve the ratio that causes the compound to be stable:

a.) STEP 1-Obtain the charges for the both the metal and nonmetal involved in forming the compound

b.) STEP 2-Write their charges as SUPERSCRIPTSc.) STEP 3-Cross the charges and make them SUBSCRIPTS for the elements.EXAMPLE.

PRACTICE 2Write the formula for the ionic compound that is formed when each of the following pairs of ions interact.a.) K+ and S -2 K2S

b.) Mg+2 and O-2 MgOc.) Ca+2 and I-1 CaI2

d.) Li+1 and N-3 Li3N

e.) Al+3 and S-2 Al2S3

VI.) NAMING IONSNames of cations and anions are formed by a system developed by the International Union of Pure and Applied Chemistry (IUPAC).

A.) Names of cations from metals that form only one type of positive ion

1.) Elements in Groups 1A, 2A and 3A and some transition elements form only one type of cations. For these ions the name of the cation is the name of the metal followed by the word “ion”:

Na+ Sodium ion K+ Potassium ion Mg+2 Magnesium ion

Al+3 Aluminum ion Ag+ Silver ion Zn+2 Zinc ion

B.) Names of cations from metals that form two different positive ions

1.) Metals in Group 4A and most transition metals form more than one type of cation, so the name of the cation must show its charge. For these ions the charge on the ion is given as a Roman numeral in

parentheses right after (with no space) the metal name.

Sn+2 Tin(II) Sn+4 Tin(IV)

Pb+2 Lead(II) Pb+4 Lead(IV)

Cu+1 Copper(I) Cu+2 Copper(II)

Fe+2 Iron(II) Fe+3 Iron(III)

Co+2 Cobalt(II) Co+3 Cobalt(III)

Hg+1 Mercury(I) Hg+2 Mercury(II)

Elements with more than one possible charge

C.) Names of anions1.) Anions are named by replacing the ending of the element name with –ide followed by the word “ion”

F-1 Fluoride ion Cl-1 Chloride

ion Br-1 Bromide ion I-1 Iodide ion

O-2 Oxide ion S-2 Sulfide ion N-3 Nitride ion P-3 Phosphide

ion

D.) Names of Polyatomic Ions1.) A POLYATOMIC ION is an ion that

contains two or more elements. You MUST MEMORIZE the names and the formulas of the following polyatomic ions.