Ionic Compounds

Forming Chemical Bonds Definition of a chemical bond: The force that holds two atoms together. This force could be: Attraction of a nucleus for electrons of another atom. Attraction of a +ion for a –ion.

Review Electron affinity - Attraction of a nucleus for electrons of another atom. Ionization energy influences formation of + ions. Noble gases have low electron affinity and high ionization energy: they do not form compounds readily.

Formation of positive ions cations All ion formation is driven by the stability of an octet of valence electrons. Metals achieve this most easily by losing 1 or more electrons.

Formation of positive ions – cations Reactivity of metals is based on how easily they lose valence electrons to form ions. Low ionization energies predict reactivity

Formation of positive ions – cations .

Formation of positive ions – cations Transition metals can form ions of different charges. Remember, all transition metals have 2 valence electrons (ns2). But, d electrons can be lost also. Pseudo noble gas configuration: a full outer energy level s, p, and d or f Ex.: Zn 1s2 2s2 2p6 3s2 3p6 4s2 3d10 Zn2+ 1s2 2s2 2p63s2 3p6 3d10

Formation of negative ions – anions

Nonmetals gain electrons to form anions. ex. Chlorine 1s2 2s2 2p6 3s2 3p5 gains 1e- Cl- 1s2 2s2 2p6 3s23p6 Electron configuration of Argon ex. Phosphorus 1s22s22p63s23p3 gains 3e- P-3 1s22s22p63s23p6

Monatomic charges by group # 1

2

3

4

5

6

7

8

+1

+2

+3

*

-3

-2

-1

**

• * varies: shares or loses • ** Noble gases do not form ions

The Formation and Nature of Ionic Bonds Definition: The electrostatic force that holds oppositely charged particles together. Binary ionic compounds: two elements; a metal and a nonmetal; cation (+) and anion (-)

Formation of an Ionic Bond .

.

Formation of an Ionic Bond (cont)

Formation of an Ionic Bond (cont) Sodium ion

chloride ion

Formation of an Ionic Bond (cont) Another example:

How would magnesium react with chlorine?

Formation of an Ionic Bond (cont) .

Formation of an Ionic Bond (cont) .

Properties of Ionic Compounds Ionic compounds exist as ionic crystals – hard solids. Quartz: silicon oxide Copper sulfate Aluminum oxide (ruby)

Properties of Ionic Compounds (cont) • Melting (solid to liquid): attraction between ions must be reduced. • Boiling (liquid to gas): attraction between ions must be further reduced. • Since the attraction between ions is strong this will take a lot of energy. Melting points and boiling points are high.

Properties of Ionic Compounds (cont) Electrical conductivity requires freely moving charged particles. Ionic compounds can only conduct electricity in the liquid state or when dissolved in water (aqueous). The term for a compound with this characteristic is electrolyte.

Properties of Ionic Compounds (cont)

The formation of ionic compounds (crystals) from positive and negative ions is always exothermic (releases energy). The energy released is also the amount it would take to break up the crystal structure. This is referred to as lattice energy.

Review: Properties of Ionic Compounds • • • •

Crystalline solids (made of ions) High melting and boiling points Conduct electricity when melted Many soluble in water but not in nonpolar liquid (ie. Oil)

Names and formulas for Ionic Compounds. Ionic compounds are not organized in molecules, but crystals. The simplest ratio of ions in an ionic compound is the formula unit. Sodium chloride is a 1:1 ratio Aluminum chloride of Na+ and Cl 1:3 ratio of Al3+ and Cl-

Formula units. Sodium chloride is a 1:1 ratio of Na+ and Cl

Aluminum chloride 1:3 ratio of Al3+,Cl-

Determining Charge. Monatomic ions (one-atom ions) can be determined from their Group A # Group 1 – loses one (*lower energy valence electrons are an octet) Group 2 – loses two (*) Group 3 – loses three(*) Group 5 – gains three (5+3=8) Group 6 – gains two (6+2=8) Group 7 – gains one (7+1=8)

Determining Charge. The charge of a monatomic ion is its oxidation number (oxidation state). Group 1 metals all form +1 cations. Group 2 metals all form +2 cations

Group 7 nonmetals all form -1 anions

Determining Charge. Most transition metals and Group 3A & 4A metals have more than one oxidation number or charge. For example, chromium, titanium, vanadium, manganese, iron, and cobalt, and lead all form +2 and +3 cations.

Writing Formulas The cation (metal +ion) is always written first. Each formula unit must be neutral. Charges must balance. Binary compounds contain a monatomic cation and a monatomic anion.

Writing Formulas Remember, the sum of the charges must add up to zero in order to form a neutral compound. The “crisscross method” is very useful— the charge on one ion becomes the subscript on the other. Always double-check to see that the subscripts are in their lowest terms!

Practice • What is the formula for the ionic compound formed by Calcium and Iodine?

Practice Step 1: Write down the symbols of the elements Ca I Step 2: Write the ionic charges above the symbols Ca 2+ I 1Step 3: Criss cross the numbers in the ionic charge. NO + or - signs Ca 2 I1 Step 4: Write the formula. No charges. Reduce subscripts.

CaI2

Aluminum and oxygen Step 1: Write down the symbols of the elements Al O Step 2: Write the ionic charges above the symbols Al 3+ O 2Step 3: Criss cross the ionic charge Al 3+ O 2Step 4: Write the formula. No charges. Reduce subscripts.

Al2O3

Calcium and nitrogen Step 1: Write down the symbols of the elements Ca N Step 2: Write the ionic charges above the symbols Ca 2+ N 3Step 3: Criss cross the ionic charge Ca 2+ N 3Step 4: Write the formula. No charges. Reduce subscripts.

Ca3N2

Practice with Transition Metals Transition metals will be given with a Roman numeral written after them – this is the charge or oxidation state. Fe (III) or Iron (III) is Fe +3 Follow normal formula writing procedure

Practice with Transition Metals Ex: chromium (V) and bromine Cr Br

Criss cross

Cr+5

Br-1

Cr+5

Br-1

CrBr5

Polyatomic Ions Definition: Ions made up of more than one atom, chemically bound. The charge is on the whole group not any one atom. Example: Phosphate ion is PO4 -3

Calcium and nitrate Step 1: Write down the symbols of the ions Ca NO3 Step 2: Write the ionic charges above the symbols Ca 2+ NO3 1Step 3: Criss cross the ionic charge Ca 2+ NO3 1Step 4: Write the formula. No charges. Use Parentheses. Reduce subscripts. Ca (NO3 )2

Naming ionic compounds Name cation (metal) first; then anion (nonmetal) Monatomic cation use the same name. Monatomic anions use the root of their name and the suffix –ide. Example: Al2O3 aluminum and oxygen Aluminum oxide

Practice naming CaI2

Calcium and Iodine Calcium iodide

Ca3N2

Calcium and nitrogen Calcium nitride

Naming transition metal compounds The charge will be written as a Roman numeral after the name of the metal. You must work backwards from the formula to figure out the charge FeCl2 Each Cl is a -1; total negative charge is -2. Only one Fe , so it must be +2 Iron (II) chloride

Naming transition metal compounds PbO2 Name the metal first: Lead Find the charge by working backwards. Each O ion is -2 so the total negative charge is -4. Positive charge must be +4 Lead(IV) Name the anion with an –ide ending

Lead(IV) oxide

Naming transition metal compounds Cu3N2 Name the metal first Copper Find the charge by working backwards. Each N ion is -3 so the total negative charge is -6. Positive charge must be +6 There are 3 copper ions; each ion must be a +2 for a total positive charge of +6 Therefore it is Copper(II) Name the anion with an –ide ending

Copper(II)nitride

Naming transition metal compounds CuBr2 Name the metal first Copper Find the charge by working backwards. Each Br ion is -1 so the total negative charge is -2. Positive charge must be +2 Copper(II) Name the anion with an –ide ending

Copper(II)bromide

Metallic Bonds Metals can not form ionic bonds with themselves or other metals. They do make lattice structures. Outer electrons are loosely held – a sea of electrons (delocalized e-). Each atom really exists as a cation and all of the outer electrons can move freely.

Metallic Properties Delocalized electrons explain metallic properties. Conduct electricity because the e- can move freely. Shiny because all of those electrons can absorb then release photons of light.

Metal Alloys Definition: a metal lattice structure with another metal (sometimes nonmetal) added to the lattice structure.

Alloys There are two main types of alloys. Substitution alloy: similar size atoms (ie.) brass is made of copper and zinc atoms. Interstitial alloy: smaller atoms “fill in holes” (ie.) steel is made of iron and carbon.