Chapter 7 Ionic and Metallic Bonding

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Transcript Chapter 7 Ionic and Metallic Bonding

Chapter 7

“Ionic and Metallic Bonding”

7.1 - Ions

Valence Electrons are…?

 

Valence electrons

– The

and

electrons in the outer energy level – the highest occupied energy level

Core

electrons – electrons in the energy levels

below

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

1) 2) 1) 2) Have the same outer electron

configuration

Have the same valence electrons.

Electron configuration of Group 1A?

– 𝒔 𝟏 Number of valence electrons in Group 1A?

–

  The number of valence electrons are easily determined. It is the

group number

for a

representative

element – Group 2A: Be, Mg, Ca, etc.

have

valence electrons

Electron Dot diagrams are…  A way of

showing

valence electrons.

  How to write them?

Write the

symbol

– 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

valence electrons to show.

 First we write the symbol.

N  Then 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.

 Practice with e- dot structure Li  N  Be  B  C  O  F  Ne

The Octet Rule 

The Octet Rule

: in forming compounds, atoms tend to achieve a

noble gas

configuration;

in the outer level  Each 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.

– Where are metals located?

Left

 Make

positive

ions

(cations)

Formation of Cations  If we look at the electron configuration, it makes sense to lose electrons:  Na

1s 2 2s 2 2p 6 3s 1

1 valence electron  Na

1+ 1s 2 2s 2 2p 6

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

valence electrons Ca

Electron Dots For Cations  Metals will

lose all valence electrons

Electron Dots For Cations  Metals will

lose the valence electrons

 Form

positive

ions Ca

2+

This is the “calcium ion”.

NO DOTS

are now shown for the cation.

Practice  # of valence electron  Cation formed  Na = 1  𝑁𝑎 +1  Mg = 2  𝑀𝑔 +2  Al = 3  𝐴𝑙 +3

The transition metals get funky…

Electron Dots For Cations  Let’s do Scandium, #21  The electron configuration is:

1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 1

 Thus, it can lose 2e

(making it 2+), or lose 3e

(making 3+) Sc =

Sc 2+

Sc =

Sc 3+

Scandium (II) ion Scandium (III) ion

Electron Dots For Cations  Let’s do Silver, element #47 

Predicted

configuration is: 1s

6 5s 2 4d 9

 

Actual

configuration is: 1s

6 5s 1 4d 10

Ag = Ag

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

Electron Dots For Cations  Silver 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

1s 2 2s 2 2p 6 3s 2 3p 4

valence electrons 

S 2-

1s 2 2s 2 2p 6 3s 2 3p 6

configuration. = noble gas 

Halide ions

- 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.

3-

P (This is called the “phosphide ion”, and

shows

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 =

stable

 This is the

octet rule

(8 in the outer level is particularly stable).

Ar

Review How many valence electrons do the following elements have?

 Ga = 3  P = 5  Cl = 7  S = 6  Mg = 2  K = 1  Li = 1  He = 2  F = 7  Ne = 8

 Review Draw the electron dot structure of the following elements.

Ga  K  P  S  Mg  He  F  Ne

Review What ions will the following elements form?

 𝐺𝑎 +3  𝑀𝑔 +2  𝑃 −3  𝐾 +1  𝐹 −1  𝑆 −2

7.2 - Ionic Bonds and Ionic Compounds

Ionic Bonding  Anions and cations are held together by

opposite charges

(+ and -)   Ionic compounds are called

salts .

Formula unit

– Simplest

ratio

of elements in an ionic compound.

Practice with Formula Unit  What is the formula unit for the following compounds?

 Formula Unit  NaCl  𝐻 2 𝑂  𝐶𝑎𝐶𝑂 3 1:1 2:1 1:1:3

Ionic Bonds  Formed through the

transfer

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

noble gas

configuration.

Ionic Compounds • 1) 2) Also called

SALTS

Made from a

CATION

and

ANION

A metal

and a

nonmetal

)

Ionic Bonding

Na Cl

• The

metal loses

its one electron from the outer level.

• The

nonmetal gains

one more to fill its outer level, and will accept the one electron that the metal is going to lose.

Ionic Bonding

Na

Cl

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

Ionic Bonding Example- combine Ca and P:

Ca P

 All electrons must be

accounted for

, and

each

atom will have a noble gas configuration (which is stable).

Ca

Ionic Bonding

P

Ionic Bonding

Ca

P

Ionic Bonding

Ca

Ca P

Ca

Ionic Bonding

P

Ca

Ionic Bonding

P

Ca

2+ Ionic Bonding

P

Ionic Bonding

Ca Ca

Ca

P P

Ionic Bonding

Ca Ca

Ca

P P

Ionic Bonding

Ca

P P

3 3-

= Ca 3 P 2 Ionic Bonding •

Chemical formula-

shows the kinds and numbers of atoms in the

smallest

representative particle of the substance.

Balancing Ionic formulas  Crisscross method  The numerical value of the

charge

of each ion is crossed over and becomes the

subscript

for the other ion.

Practice What will the chemical formula look like?

 Elements  Formula  Ca+2  Al+3  Ca+2 F O-2 O-2  𝐶𝑎𝐹 2  𝐴𝑙 2 𝑂 3  𝐶𝑎𝑂

 Properties of Ionic Compounds

1. Crystalline

solids – regular repeating arrangement of ions 

Strongly

bonded together.

 Structure is

rigid

High melting points Coordination

number number of ions of opposite charge surrounding it

NaCl CsCl TiO

2 - 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

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

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.

Review What is the formula unit for the following compounds?

 KCl 1:1  𝐹𝑒 2 𝑂 3 2:3  𝐹𝑒𝑆 2 1:2  𝐵𝑎𝑆𝑂 4 1:1:4  HgS 1:1  𝑁𝑎 2 𝑂 2:1

Practice What will the chemical formula look like?

 Elements  Na+ Cl     Mg+2 Ca+2 Al+3 K+ F N-3 N-3 S-2  Formula  𝑁𝑎𝐶𝑙  𝑀𝑔𝐹 2  𝐶𝑎 3 𝑁 2  𝐴𝑙𝑁  𝐾 2 𝑆

7.3 – Bonding in Metals

Metallic Bonds are…  How do we get sheets of Aluminum (or any metal)?

 Metals hold on to their valence electrons

very weakly

 Think of them as positive ions (cations) floating in a sea of electrons

Sea of Electrons  Electrons are free to

move

through the solid.

 Metals

conduct

electricity.

+ + + + + + + + + + + +

Metals are Malleable 

Hammered

into shape (bend).



Ductile

- drawn into wires.

 Both malleability and ductility explained in terms of the

mobility

of the valence electrons

- Page 201 Due to the mobility of the valence electrons, metals have: 1) Ductility

and

2) Malleability

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  Metals are arranged in very

compact

and orderly

patterns

Alloys 

Alloys

mixtures of 2 or more elements, at least 1 is a metal  Made by

melting

a mixture of elements, 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

• END The

Predicting Ionic Charges

Group B elements: Many transition elements have more than one possible oxidation state.

Note the use of

Roman Iron (II) = Fe 2+ numerals

to show charges

Iron (III) = Fe 3+

Naming cations  Two methods can clarify when more than one charge is possible:

1) Stock system

numerals

– uses

roman

in parenthesis to indicate the numerical value

2) Classical method

word with

suffixes

– uses root (-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 post-transition elements also have more than one possible oxidation state.

Tin (II) = Sn 2+ Lead (II) = Pb 2+ Tin (IV) = Sn 4+ Lead (IV) = Pb 4+

Predicting Ionic Charges

Group B elements:Some transition elements have

only one

as these three: Silver = Ag 1+ possible oxidation state, such Zinc = Zn 2+ Cadmium = Cd 2+

Exceptions:  Some of the transition metals have only one ionic charge: –

Do not

need to use roman numerals for these: – Silver is

always

1+ (

Ag 1+ )

– Cadmium 2+ (

Cd 2+

and Zinc and

Zn 2+

) are

always

Practice by naming these: 

Na 1+



Ca 2+



Al 3+



Fe 3+



Fe 2+



Pb 2+



Li 1+

Write symbols for these:  Potassium ion  Magnesium ion  Copper (II) ion  Chromium (VI) ion  Barium ion  Mercury (II) ion

Naming Anions  Anions are always the same charge  Change the monatomic element ending to – ide 

F 1-

a Fluorine atom will become a Fluoride ion.

Practice by naming these: 

Cl 1-



N 3-



Br 1-



O 2-



Ga 3+

Write symbols for these: 

Sulfide ion



Iodide ion



Phosphide ion



Strontium 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:

C 2 H 3 O 2 1-

 Nitrate:

NO 3 1-

  Nitrite:

NO 2 1-

Permanganate:

MnO 4 1-

 Hydrox ide :

OH 1-

and Cyan ide :

CN 1-

Know Table 9.3 on page 257      Sulfate:

SO 4 2-

Sulfite:

SO 3 2-

  Carbonate:

CO 3 2-

Chromate:

CrO 4 2-

Dichromate:

Cr 2 O 7 2-

 Phosphate:

PO 4 3-

Phosphite:

PO 3 3-

Ammonium:

NH 4 1+

(One of ions)