chapter 7 “ionic and metallic bonding”

Chapter 7

“Ionic and Metallic Bonding”

Valence Electrons are…? The electrons responsible for the

chemical properties of atoms, and are those in the outer energy level.

Valence electrons - The s and p electrons in the outer energy level

–the highest occupied energy level Core electrons – are those in the

energy levels below.

Keeping Track of Electrons Atoms in the same column...

1) Have the same outer electron configuration.

2) Have the same valence electrons. The number of valence electrons are

easily determined. It is the group number for a representative element

Group 2A: Be, Mg, Ca, etc.

– have 2 valence electrons

Electron Dot diagrams are… A way of showing & keeping

track of valence electrons. How to write them? Write the symbol - it

represents the nucleus and inner (core) electrons

Put one dot for each valence electron (8 maximum)

They don’t pair up until they have to (Hund’s rule)

X

The Electron Dot diagram for Nitrogen

Nitrogen has 5 valence electrons to show.

First we write the symbol. NThen add 1 electron at a time to each side.Now they are forced to pair up.

We have now written the electron dot diagram for Nitrogen.

The Octet Rule In Chapter 6, we learned that noble gases

are unreactive in chemical reactions In 1916, Gilbert Lewis used this fact to

explain why atoms form certain kinds of ions and molecules

The Octet Rule: in forming compounds, atoms tend to achieve a noble gas configuration; 8 in the outer level is stableEach noble gas (except He, which has

2) has 8 electrons in the outer level

Formation of Cations Metals lose electrons to attain a noble

gas configuration. They make positive ions (cations) If we look at the electron configuration,

it makes sense to lose electrons: Na 1s22s22p63s1 1 valence electron Na1+ 1s22s22p6 This is a noble gas

configuration with 8 electrons in the outer level.

Electron Dots For Cations Metals will have few valence electrons

(usually 3 or less); calcium has only 2 valence electrons

Ca

Electron Dots For Cations Metals will have few valence electrons Metals will lose the valence electrons

Ca

Electron Dots For Cations Metals will have few valence electrons Metals will lose the valence electrons Forming positive ions

Ca2+NO DOTS are now shown for the cation.

This is named the “calcium ion”.

Electron Dots For CationsLet’s do Scandium, #21The electron configuration is:

1s22s22p63s23p64s23d1

Thus, it can lose 2e- (making it 2+), or lose 3e- (making 3+)

Sc = Sc2+ Scandium (II) ion Scandium (III) ion

Sc = Sc3+

Electron Dots For CationsLet’s do Silver, element #47Predicted configuration is:

1s22s22p63s23p64s23d104p65s24d9

Actual configuration is: 1s22s22p63s23p64s23d104p65s14d10

Ag = Ag1+ (can’t lose any more, charges of 3+ or greater are uncommon)

Electron Dots For CationsSilver did the best job it

could, but it did not achieve a true Noble Gas configuration

Instead, it is called a “pseudo-noble gas configuration”

Electron Configurations: Anions Nonmetals gain electrons to attain

noble gas configuration. They make negative ions (anions) S = 1s22s22p63s23p4 = 6 valence

electrons S2- = 1s22s22p63s23p6 = noble gas

configuration. Halide ions are ions from chlorine or

other halogens that gain electrons

Electron Dots For Anions Nonmetals will have many valence

electrons (usually 5 or more) They will gain electrons to fill outer shell.

P 3-(This is called the “phosphide ion”, and should show dots)

Stable Electron Configurations All atoms react to try and achieve a

noble gas configuration. Noble gases have 2 s and 6 p electrons. 8 valence electrons = already stable! This is the octet rule (8 in the outer level

is particularly stable).

Ar

Ionic Bonding Anions and cations are held together

by opposite charges (+ and -) Ionic compounds are called salts. Simplest ratio of elements in an ionic

compound is called the formula unit. The bond is formed through the

transfer of electrons (lose and gain) Electrons are transferred to achieve

noble gas configuration.

Ionic Compounds

1) Also called SALTS

2) Made from: a CATION with an ANION (or literally from a metal combining with a nonmetal)

Ionic Bonding

Na ClThe metal (sodium) tends to lose its one electron from the outer level.

The nonmetal (chlorine) needs to gain one more to fill its outer level, and will accept the one electron that sodium is going to lose.

Ionic Bonding

Na+ Cl -

Note: Remember that NO DOTS are now shown for the cation!

Ionic Bonding

All the electrons must be accounted for, and each atom will have a noble gas configuration (which is stable).

Ca P

Lets do an example by combining calcium and phosphorus:

Ionic Bonding

Ca P

Ionic Bonding

Ca2+ P

Ionic Bonding

Ca2+ P

Ca

Ionic Bonding

Ca2+ P 3-

Ca

Ionic Bonding

Ca2+ P 3-

Ca P

Ionic Bonding

Ca2+ P 3-

Ca2+ P

Ionic Bonding

Ca2+ P 3-

Ca2+ P

Ca

Ionic Bonding

Ca2+ P 3-

Ca2+ P

Ca

Ionic Bonding

Ca2+ P 3-

Ca2+P

3-

Ca2+

Ionic Bonding

= Ca3P2Formula Unit

This is a chemical formula, which shows the kinds and numbers of atoms in the smallest representative particle of the substance.

For an ionic compound, the smallest representative particle is called a: Formula Unit

Properties of Ionic Compounds1. Crystalline solids - a regular repeating

arrangement of ions in the solid: Fig. 7.9, page 197

– Ions are strongly bonded together.– Structure is rigid.

2. High melting points Coordination number- number of ions

of opposite charge surrounding it

- Page 198

Coordination Numbers:

Both the sodium and chlorine have 6

Both the cesium and chlorine have 8

Each titanium has 6, and each oxygen has 3

NaCl

CsCl

TiO2

Do they Conduct? Conducting electricity means allowing

charges to move. In a solid, the ions are locked in place. Ionic solids are insulators. When melted, the ions can move around.3. Melted ionic compounds conduct.

– NaCl: must get to about 800 ºC.– Dissolved in water, they also conduct

(free to move in aqueous solutions)

- Page 198

The ions are free to move when they are molten (or in aqueous solution), and thus they are able to conduct the electric current.

Metallic Bonds are…How metal atoms are held

together in the solid.Metals hold on to their valence

electrons very weakly.Think of them as positive ions

(cations) floating in a sea of electrons: Fig. 7.12, p.201

Sea of Electrons

+ + + ++ + + +

+ + + +

Electrons are free to move through the solid.

Metals conduct electricity.

Metals are MalleableHammered into shape (bend).Also ductile - drawn into wires.Both malleability and ductility

explained in terms of the mobility of the valence electrons

- Page 201

1) Ductility 2) Malleability

Due to the mobility of the valence electrons, metals have:

and

Notice that the ionic crystal breaks due to ion repulsion!

Malleable

+ + + ++ + + +

+ + + +

Force

Malleable

+ + + +

+ + + ++ + + +

Mobile electrons allow atoms to slide by, sort of like ball bearings in oil.

Force

Ionic solids are brittle

+ - + -+- +-

+ - + -+- +-

Force

Ionic solids are brittle

+ - + -

+- +-+ - + -

+- +-

Strong Repulsion breaks a crystal apart, due to similar ions being next to each other.

Force

Crystalline structure of metal If made of one kind of atom,

metals are among the simplest crystals; very compact & orderly

Note Fig. 7.14, p.202 for types:1. Body-centered cubic:

–every atom (except those on the surface) has 8 neighbors

–Na, K, Fe, Cr, W

Crystalline structure of metal2. Face-centered cubic:

–every atom has 12 neighbors

–Cu, Ag, Au, Al, Pb

3. Hexagonal close-packed

–every atom also has 12 neighbors

–different pattern due to hexagonal

–Mg, Zn, Cd

Alloys We use lots of metals every day,

but few are pure metals Alloys are mixtures of 2 or more

elements, at least 1 is a metal made by melting a mixture of the

ingredients, then cooling Brass: an alloy of Cu and Zn Bronze: Cu and Sn

Why use alloys? Properties are often superior to the pure

element Sterling silver (92.5% Ag, 7.5% Cu) is

harder and more durable than pure Ag, but still soft enough to make jewelry and tableware

Steels are very important alloys

– corrosion resistant, ductility, hardness, toughness, cost

More about Alloys… Table 7.3, p.203 – lists a few alloys Types? a) substitutional alloy- the

atoms in the components are about the same size

b) interstitial alloy- the atomic sizes quite different; smaller atoms fit into the spaces between larger

“Amalgam”- dental use, contains Hg

Atoms and Ions - Naming Atoms are electrically neutral.

– Because there is the same number of protons (+) and electrons (-).

Ions are atoms, or groups of atoms, with a charge (positive or negative)– They have different numbers of protons

and electrons. Only electrons can move, and ions

are made by gaining or losing electrons.

An Anion is… A negative ion. Has gained electrons. Nonmetals can gain electrons. Charge is written as a superscript on

the right.

F1-Has gained one electron (-ide is new ending = fluoride)

O2- Gained two electrons (oxide)

A Cation is… A positive ion. Formed by losing electrons. More protons than electrons. Metals can lose electrons

K1+ Has lost one electron (no name change for positive ions)

Ca2+ Has lost two electrons

Predicting Ionic ChargesGroup 1AGroup 1A:: Lose 1 electron to form Lose 1 electron to form 1+1+ ions ions

HH11++ LiLi11++ NaNa11++ KK11++ RbRb11++

Predicting Ionic ChargesGroup 2AGroup 2A:: Loses 2 electrons to form Loses 2 electrons to form 2+2+ ions ions

BeBe2+2+ MgMg2+2+ CaCa2+2+ SrSr2+2+ BaBa2+2+

Predicting Ionic ChargesGroup 3AGroup 3A:: Loses 3 Loses 3

electrons to form electrons to form 3+3+ ions ions

BB3+3+ AlAl3+3+ GaGa3+3+

Predicting Ionic ChargesGroup 4AGroup 4A:: Do they Do they loselose 4 electrons or 4 electrons or gaingain 4 electrons? 4 electrons?

Neither! Neither! Group 4A Group 4A elements rarely form elements rarely form

ions ions (they (they tend to tend to share)share)

Predicting Ionic ChargesGroup 5AGroup 5A:: Gains 3 Gains 3 electrons to form electrons to form 3-3- ions ions

NN3-3-

PP3-3-

AsAs3-3-

Nitride

Phosphide

Arsenide

Predicting Ionic ChargesGroup 6AGroup 6A:: Gains 2 Gains 2 electrons to form electrons to form 2-2- ions ions

OO2-2-

SS2-2-

SeSe2-2-

Oxide

Sulfide

Selenide

Predicting Ionic ChargesGroup 7AGroup 7A:: Gains 1 Gains 1 electron to form electron to form 1-1- ions ions

FF1-1-

ClCl1-1-

BrBr1-1-Fluoride

Chloride

Bromide

II1-1- Iodide

Predicting Ionic ChargesGroup 8AGroup 8A:: Stable Stable noble gases noble gases do notdo not form ions!form ions!

Predicting Ionic ChargesGroup B elementsGroup B elements:: Many Many transitiontransition elements elements

have have more than onemore than one possible oxidation state. possible oxidation state.Iron (II) = Fe2+

Iron (III) = Fe3+

Note the use of Roman numerals to show charges

Naming cations Two methods can clarify when

more than one charge is possible:

1) Stock system – uses roman numerals in parenthesis to indicate the numerical value

2) Classical method – uses root word with suffixes (-ous, -ic)• Does not give true value

Naming cations We will use the Stock system. Cation - if the charge is always the

same (like in the Group A metals) just write the name of the metal.

Transition metals can have more than one type of charge.– Indicate their charge as a roman

numeral in parenthesis after the name of the metal (Table 9.2, p.255)

Predicting Ionic Charges Some of the Some of the post-transitionpost-transition elements also elements also have have more than onemore than one possible oxidation state. possible oxidation state.Tin (II) = Sn2+ Lead (II) = Pb2+

Tin (IV) = Sn4+ Lead (IV) = Pb 4+

Predicting Ionic ChargesGroup B elementsGroup B elements:: Some Some transitiontransition elements elements have have only oneonly one possible oxidation state, such possible oxidation state, such as these three:as these three:

Zinc = Zn2+Silver = Ag1+ Cadmium = Cd2+

Exceptions:Some of the transition metals

have only one ionic charge:

–Do not need to use roman numerals for these:

–Silver is always 1+ (Ag1+)

–Cadmium and Zinc are always 2+ (Cd2+ and Zn2+)

Practice by naming these: Na1+ Ca2+ Al3+ Fe3+ Fe2+ Pb2+ Li1+

Write symbols for these:

Potassium ionMagnesium ion Copper (II) ionChromium (VI) ionBarium ionMercury (II) ion

Naming AnionsAnions are always the

same chargeChange the monatomic

element ending to – ideF1- a Fluorine atom will

become a Fluoride ion.

Practice by naming these:Cl1- N3- Br1- O2-

Ga3+

Write symbols for these:

Sulfide ionIodide ionPhosphide ionStrontium ion

Polyatomic ions are… Groups of atoms that stay together and

have an overall charge, and one name. Usually end in –ate or -ite

Acetate: C2H3O21-

Nitrate: NO31-

Nitrite: NO21-

Permanganate: MnO41-

Hydroxide: OH1- and Cyanide: CN1-?

Sulfate: SO42-

Sulfite: SO32-

Carbonate: CO32-

Chromate: CrO42-

Dichromate: Cr2O72-

Phosphate: PO43-

Phosphite: PO33-

Ammonium: NH41+

Know Table 9.3 on page 257

If the polyatomic ion begins with H, then combine the word hydrogen with the other polyatomic ion present: H1+ + CO3

2- → HCO3

1-

hydrogen + carbonate → hydrogen carbonate ion

(One of the few positive polyatomic ions)

Writing Ionic Compound Formulas

Example: Barium nitrate (note the 2 word name)

1. Write the formulas for the cation and anion, including CHARGES!

BaBa2+2+ NONO33--

2. Check to see if charges are balanced. 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance subscripts.

Not balanced!

( )( ) 22

Now balanced.

= Ba(NO3)2

Writing Ionic Compound Formulas

Example: Ammonium sulfate (note the 2 word name)

1. Write the formulas for the cation and anion, including CHARGES!

NHNH44++ SOSO44

2-2-

2. Check to see if charges are balanced.

3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance the subscripts.

Not balanced!

( )( )22

Now balanced.

= (NH4)2SO4

Writing Ionic Compound Formulas

Example: Iron (III) chloride (note the 2 word name)

1. Write the formulas for the cation and anion, including CHARGES!

FeFe3+3+ClCl--

2. Check to see if charges are balanced.

3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance the subscripts.

Not balanced!

33

Now balanced.= FeCl3

Writing Ionic Compound Formulas

Example: Aluminum sulfide (note the 2 word name)

1. Write the formulas for the cation and anion, including CHARGES!

AlAl3+3+ SS2-2-

2. Check to see if charges are balanced.

3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance the subscripts.

Not balanced!

22 33

Now balanced.= Al2S3

Writing Ionic Compound Formulas

Example: Magnesium carbonate (note the 2 word name)1. Write the formulas for the cation and anion, including CHARGES!

MgMg2+2+ COCO332-2-

2. Check to see if charges are balanced.

They are balanced!

= MgCO3

Writing Ionic Compound Formulas

Example: Zinc hydroxide (note the 2 word name)

1. Write the formulas for the cation and anion, including CHARGES!

ZnZn2+2+ OHOH--

2. Check to see if charges are balanced. 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance the subscripts.

Not balanced!

( )( )22

Now balanced.= Zn(OH)2

Writing Ionic Compound Formulas

Example: Aluminum phosphate (note the 2 word name)

1. Write the formulas for the cation and anion, including CHARGES!

AlAl3+3+ POPO443-3-

2. Check to see if charges are balanced.

They ARE balanced!

= AlPO4

Naming Ionic CompoundsNaming Ionic Compounds 1. Name the cation first, then anion

2. Monatomic cation = name of the element

Ca2+ = calcium ion

3. Monatomic anion = root + -ide

Cl = chloride

CaCl2 = calcium chloride

Naming Ionic CompoundsNaming Ionic Compounds

some metals can form more than one charge (usually the transition metals)

use a Roman numeral in their name:

PbCl2 – use the anion to find the charge

on the cation (chloride is always 1-)

Pb2+ is the lead (II) cation

PbCl2 = lead (II) chloride

(Metals with multiple oxidation states)(Metals with multiple oxidation states)

Things to look for:

1) If cations have ( ), the number in parenthesis is their charge.

2) If anions end in -ide they are probably off the periodic table (Monoatomic)

3) If anion ends in -ate or –ite, then it is polyatomic

Practice by writing the formula or name as required…

Iron (II) PhosphateStannous FluoridePotassium SulfideAmmonium ChromateMgSO4

FeCl3