Ionic CompoundsChapter 8

I will define a chemical bondI will describe how ions formI will identify ionic bonding and the characteristics of ionic compoundsI will name and write chemical formulas for ionic compoundsI will relate metallic bonds to the characteristics of metals

Several slides from:http://www.kentchemistry.com/

Forming Chemical Bonds

I will define chemical bond

I will relate chemical bond formation to electron configuration

I will describe the formation of positive and negative ions

Vocabulary: chemical bond, cation, anion

Chemical Bond

A force that holds two atoms together

Form in two ways:By the attraction between a positive nucleus and negative electrons

By the attraction between a positive ion and a negative ion

Recall:Valence electrons are involved in the formation of chemical bonds between 2 atoms

Atoms want 8 valence electrons so they have a stable electron structure (helium only needs 2)

Positive ions form when an atom loses one or more valence electrons in order to attain a full outer shell

Formation of Positive Ions

CationA positively charged ion

atom + ionization energy = ion+ + electron(s)

Which Elements Form Positive Ions?

Group 1ALose 1 electron

Form +1 ions

Group 2ALose 2 electrons

Form +2 ions

Transition Metals (DIFFICULT to predict)

Outer energy level ns2 (in general)

L R atoms of each element are also filling in the d sublevel

Commonly lose their 2 valence electrons (form+2 ions)

Also possible for d electrons to be lost

Allows them to form +3 ions or greater

Group 3A (a few)Lose 3 electrons

Form +3 ions

Negative ions form when an atom gains one or more valence electrons in order to attain a full outer shell

Formation of Negative Ions

AnionA negatively charged ion

atom + electron(s) = ion-- + electron affinity

Which Elements Form Negative Ions?

To designate an anion, the ending –ide is added to the root name of the element

Ex NaCl = sodium chloride

Some nonmetals can gain or lose other numbers of electrons to form an octet

Ex phosphorousGain 3 electrons

Or

Lose 5 electrons

MORE LIKELY to GAIN 3!!

NonmetalsGain the number of electrons that when added to their valence electrons, equals 8

The number of electrons gained corresponds to their negative charge

Ex gain 2 electrons = form --2 ions

Review- Ions that formLook at electron configurations (valence electrons)Metals lose electrons (+ ions)Nonmetals gain electrons (- ions)Typical charges of ions that form

The Formation and Nature of Ionic Bonds

I will describe the formation of ionic bonds

I will account for many of the physical properties of an ionic compound

I will discuss the energy involved in the formation of an ionic bond

Vocabulary: ionic bond, electrolyte, lattice energy

Formation of an Ionic Bond

Ionic BondThe electrostatic force that holds oppositely charged particles together (opposite charge attraction)

Ionic CompoundCompounds that contain ionic bonds

Examples:Oxides

Formed if ionic bonds are made between metals and the nonmetal oxygen

SaltsMost other ionic compounds

Formation of an Ionic Bond

Binary Compounds

Contain ONLY 2 different elements

Contain:Metallic cation

Nonmetallic anion

Which compound is Binary?

MgO CaSO4

Formation of an Ionic Bond

The number of electrons lost must EQUAL the number of electrons gained

Aka: the overall charge on one unit of the compound must be ZERO

Example 1:Na and Cl

1 Na ion (+1) + 1 Cl ion (-1) = (+1) + (-1) = 0

NaCl

Example 2:Ca and F

1 Ca ion (+2) + 1 F ion (-1) + 1 F ion (-1) = (+2) + (-1) + (-1) = 0

CaF2

Properties of Ionic Compounds

Chemical bonds that occur btwn atoms determine physical properties

Ionic compounds (cations + anions)Regular repeating patterns

Balance forces of attraction/repulsion

Called ionic crystal1-to-1 ratios of ions produce a cubic crystal

Ex. salt

Conductivity Demonstration

. Do ionic compounds conduct electricity?

** First…what do you need to conduct electricity??You need freely moving charged particles.

1. Solid –2. Aqueous solution –3. Liquid –

do not conduct…why not?do conduct…why?

do conduct…why?*** electrolyte: an ionic compound whose aqueous solution conducts an electric current

Properties of Ionic Compounds

Crystal Lattice structure – 3D geometric arrangement of ions (positive to negative)

Makes them hard – strong bonds

Makes them brittle – attracted only to opposite charges/repelled by like charges

Have high melting/boiling points

Properties of Ionic Compounds

Lattice EnergyEnergy required to separate 1 mole of ions of an ionic compound

Also the energy given off when the ions bond (Exothermic)

I think of this as “ionic bond energy” – how strong the bond is…

*Charge – the larger the charge, the larger the lattice energy

Size – the larger the radius, the smaller the lattice energy

NaBr, CaCl2, KI, MgO, CaO, BaI2, RbI (rank)

RbI < KI < BaI2 < CaCl2 < CaO < MgO

Names and Formulas for Ionic Compounds

I will write formulas for ionic compounds and oxyanions

I will name ionic compounds and oxyanions

Vocabulary: formula unit, monatomic ion, oxidation number, polyatomic ion, oxyanion

Names and Formulas of Ionic Compounds

A. Formula unit – the simplest ratio of ions in an ionic compound (the formula or “molecule” of an ionic compound)

B. Types of ions

1. monatomic ions one atom makes up the charged particle

2. Polyatomic ions many atoms make up the charged particle (treat these as units for balancing formulas)

C. Oxidation number

1. the charge of the ion (atom)2. Atoms’ oxidation states add up to the

charge of the ion (add up to zero if neutral)

Naming Binary Ionic Compounds

Rules

The cation (positive ion) is named first, the anion second.

Monoatomic cations take the element name.Na+ Sodium

Ca2+ Calcium

Monoatomic anions take the elements name and ends with “–ide”

Cl- Chloride

ExNaCl Sodium Chloride

Li3N Lithium Nitride Help

Polyatomic Ions

Polyatomic IonsA molecule made up of 2 or more atoms that bears ionic groups (a molecule with a charge)

OxyanionsNegative polyatomic ions with oxygenPrefix Suffix Exampl

e Names

Per- (more than)

-ate (largest #)

ClO4- perchlorate

-ate (large #) ClO3- chlorate

-ite (smaller #)

ClO2- chlorite

Hypo- (less than)

-ite (smallest #) ClO- hypochlorite Help

Naming Compounds with Polyatomic Ions

Name the cation (+ion) first (watch for NH4

+….ammonium)

Name the anion (-ion) second

NO prefixes….except dichromate

Hydrogen carbonate is also bicarbonate

Hydrogen sulfate is also called bisulfate

Help

Naming Ionic Compounds using Roman Numerals

Naming ionic compounds when the CATION is of variable charge

Happens because some elements have more than one oxidation number

Roman numeral tells us which oxidation # we have

To determine the oxidation # of the cation use your anion

Help

Some of the Elements with more than one Oxidation

Number

Naming Ionic Compounds using Roman Numerals

Example:

Pb(NO3)4 write the name "lead nitrate".

Since lead has more than one oxidation state we must figure out which lead we have.

Since each nitrate (4 of them) has a 1- charge, the Pb must be 4+.

So our roman numeral will be (IV).

Pb(NO3)4 is named "lead(IV) nitrate"

Writing Formulas

Identify the symbol of the cation (first part of the name) and the anion

Identify the valence or charge of each symbol and place it in parenthesis just above the symbol.

silver is 1+, Zinc is 2+ and Aluminum is 3+

Transition elements (have a few charges) will have a Roman Numeral to tell you what positive charge to use

Writing Formulas

Balance the total positive and negative charge on the cation and anion.

MUST add up to ZERO.

If NOT then we ask how many of each ion must we have in order to balance the charge.

Once you have determined the number of units of the cation and anion those become the subscripts which are placed right after the respective symbol.

Writing Formulas

Ex

iron (III) sulfide Fe (+3) S(-2)

2Fe ions x (+3) = +6

3S ions x (-2) = -6

Net charge = 0

Formula =Fe2S3

Metallic Bonds and Properties of Metals

I will describe a metallic bond

I will explain the physical properties of metals in terms of metallic bonds

I will define and describe alloys

Vocabulary: electron sea model, delocalized electrons, metallic bond, alloy

Metallic Bonds

Metals DO NOT bond ionicallyDO NOT share or lose electrons to form ions with other metals

They DO form crystal lattices (similar to ionic ones)

8-12 other metal atoms surround each metal atom

What do metals do???In their crystal lattice, the outer energy levels of the metal atoms overlap

Metallic Bonds

Electron Sea ModelAll metal atoms in a metallic solid contribute their valence electrons to form a “sea” of electrons

forming metallic cations

Electrons in outer energy level of bonding metallic atoms are NOT held by any specific atom

Electrons can MOVE EASILY from one atom to the next— “delocalized electrons”

Metallic BondsMetallic Bond

Attraction of the metallic cation (metal atom that released its valence electrons to the “sea”) to delocalized electrons (“the sea”)

A. Outermost electrons wander freely through metal. Metal consists of cations held together by negatively-charged electron "glue.”

Properties of Metals

B. Free electrons can move rapidly in response to electric fields, hence metals are a good conductor of electricity.

C. Free electrons can transmit kinetic energy rapidly, hence metals are good conductors of heat.

D. The layers of atoms in metal are hard to pull apart because of the electrons holding them together, hence metals are durable (tough).

But individual atoms are not held to any other specific atoms, hence atoms slip easily past one another. Thus metals are ductile. (can be drawn into wire)

Properties of Metals

Moderately high melting points (vary greatly)

Cations and electrons can slide past each other

Very high boiling pointsMore extreme-must separate cations from electrons

MalleableCan be hammered into sheets

Lustrous (shiny)Light reflects off electron sea when polished

An applied force causes metal ions to move through delocalized electrons. “layers of atoms slide over each other”

Metal Alloys

AlloyA mixture of elements that has metallic properties

Properties of an alloy differ somewhat from the properties of the elements they contain

Two types:Substitutional

Atoms of original metallic solid replaced by other metal atoms of similar size

Ex sterling silver, brass, pewter, 10-karat gold

InterstitialFormed when small holes in a metallic crystal are filled with smaller atoms (like pouring sand into a bucket of gravel)

Ex carbon steel

Metal Alloys