Compare and Contrast: Ionic Compounds vs Metals

Ye are the salt of the earth: but if the salt have lost his savour, wherewith shall it be salted? It is thenceforth good for nothing, but to be cast out, and to be trodden under foot of men. ~ Matthew 5:13 PS 110A Hatch Ch. 2222-2

Compare and Contrast: Metals vs NonNon-Metals Metals Large atoms Few valence electrons Low ionization energies Easy remove electrons

Network Solids High melting T’s Brittle solids Don’t conduct heat and electricity in solid Often colorless and usually transparent in big chunks (White

Network Solids High melting T’s Malleable Good conductors of heat and electricity in solid Opaque, with a luster

when powdered)

WHY?

Why??? Many closely spaced energy levels PS 110A Hatch Ch. 2222-3 with mobile electrons

Valence Electrons ? freedom

Non-metals Small atoms Many valence electrons High ionization energies Easily gain electrons

etc

P1: Fill up these levels for the metal magnesium and determine how many valence electrons this atom will give up easily.

3

2

1 Why do metals and non-metals react? Principles of reactivity: materials react to lower energy and increase entropy of universe PS 110A Hatch Ch. 22--4

PS 110A Hatch Ch. 22 4

How can energy be lowered? Metals lose valence electrons Non-metals gain valence electrons

PS 110A Hatch Ch. 2222-5

Why are comparable energy levels lower in chlorine?

Process “slips” downhill energetically

1. The Cl nucleus has 17 protons compared with Na’s 11.

PS 110A Hatch Ch. 2222-6

2. The electrons are pulled closer to the nucleus in Cl. (Remember the atomic size trend of the PS 110A Hatch Ch. 2222-7 Periodic Table.)

What are the products? IONS

Structure of salts – ionic bond ¾

Positively charged Sodium ions (11 protons, 10 electrons)

Negatively charged Chloride ions 17 protons, 18 electrons

Electrons belong to individual ions; they are not shared among ions. The charged ions then attract strongly---ionic bonding.

bond: electromagnetic attractions of negative and positive ions

Example: 2Na + Cl2 = 2NaCl

Demo: crystal models

PS 110A Hatch Ch. 2222-8

PS 110A Hatch Ch. 2222-9

Compare and Contrast Electron Location & Mobility

What about entropy change?

In going from Na and Cl ions to NaCl salt there is an disorder decrease, but the heat and light given off to surroundings cause an overall increase in entropy.

PS 110A Hatch Ch. 2222-10

Compare and Contrast Energy Levels

Metals

Ionic Compounds

2Na + Cl2 = 2NaCl + lots of heat and light -

+

-

+

-

+

-

+

-

Electrons – fixed; localized on individual nucleus (spherical shapes). Atomic types of orbitals.

Sea of Electrons – mobile; electron density is spread out over many nuclei PS 110A Hatch Ch. 2222-11

Examples of Ionic Compounds NaCl

Al2O3

Ions: same size charge Ions: different size and similar diameter charge and diameter

Na2O

Ions: similar diameter, but different charges

P2: Why is the size of sodium (yellow) smaller than chlorine (green).? IONIC COMPOUND ENERGY LEVELS

few levels -- spaced very far apart

many closely spaced levels spread out over many nuclei PS 110A Hatch Ch. 2222-12

Describe the structure of each compound: Do ions of one type cluster together? What type of ion immediately surrounds a specific ion? How do the answers to these two questions relate to the electric force law? What prediction could you make about the arrangement of ions in any ionic compound? PS 110A Hatch Ch. 2222-13

How does the model explain properties of salts (ionic compounds) ? High melting and boiling temperatures?

Conductivity Don’t conduct as a solid. Why? Do conduct when molten or dissolved. Why? (Crud in the water is why the hairdryer kills you.) They are called “electrolytes”.

Strong attractions between + and – ions Attractive forces act over fairly large atomic distances.

Brittleness? Strong repulsions when shifting layers. Ions with like charge come together; material shatters to relieve the stress. PS 110A Hatch Ch. 2222-14

Salts are generally transparent to light

PS 110A Hatch Ch. 2222-15

Colored crystals Why are some ionic materials colored?

Why are they transparent? – electron orbitals are localized around individual ions with FEW energy levels, that is, widely spaced – most visible photons are not absorbed, just transmitted

They may appear white when powdered or cracked. UV absorbed

Because they contain “transition” metals with more energy levels for electrons Example: Ruby and Sapphire Red is not absorbed, but is reflected. This gives ruby the red color.

PS 110A Hatch Ch. 2222-16

Metal - Nonmetal Bond “Ionic Bond”

The octet rule

Na Sodium Atom + Na + Sodium Ion

PS 110A Hatch Ch. 2222-17

Cl Chlorine Atom Cl Chloride Ion

How do we determine how many electrons an element tends to gain or lose? PS 110A Hatch Ch. 2222-18

Atoms will most likely form an ion that has the ns2np6 configuration of the closest noble gas atom. Metals take on this configuration by losing electrons Non-metals take on this configuration by gaining electrons

PS 110A Hatch Ch. 2222-19

What Ions Usually Form? Valence Electrons of Main Group Elements

P3:Beryllium (Be) will most likely form an ion with what charge?

Unreactive noble gases don’t form ions.

a) b) c) d)

-1 -2 +1 +2

Non-metals gain enough valence electrons to become “noble”. PS 110A Hatch Ch. 2222-20

Metals lose their valence electrons.

The periodic chart tells us the primary “oxidation state” state”

Families Chlorine and Fluorine will form the same types of compounds since their valence electrons are the same number and same orbital type. 3d 3p 3s

3d 3p 3s

2p 2s

2p 2s

9F

17Cl 1s

1s

PS 110A Hatch Ch. 2222-22

Predicting Formulas for Salts Find the number of electrons lost by metal atom and number gained by the non-metal. The final number lost by metals must equal final number gained by non-metal ions. Use the number lost/gained for the other atom’s subscript. Examples Mg and O Ca and P Li and N

Mg 2+ & O 2-- Æ MgO Ca 2+ & P 3- Æ Ca3P2 Li + & N 3- Æ Li3N

PS 110A Hatch Ch. 2222-21

PS 110A Hatch Ch. 2222-24

Oxidation State : a signed (+ or -) number which indicates how many electrons an atom has lost + (or could easily lose) or gained - (or could easily gain). Negative oxidation states indicate that it is energetically favorable for an atom to gain electrons Examples: Sodium +1 Beryllium +2 Chlorine -1 Sulfur -2 Hey! Its related to the group number on the periodic table! PS 110A Hatch Ch. 2222-23

Forming a salt P4: What would the chemical formula for

a) b) c) d)

magnesium fluoride (a salt of Mg and F) be? MgF Mg2F MgF2 MgF3 PS 110A Hatch Ch. 2222-25

Ionic compounds are neutral (no net charge). What are the ionic charges in the following compounds? NaCl

Na+1 and Cl-1

KBr

K+1

MgF2

Mg+2 and F-1

Al2O3

Al+3 and O-2

and

The periodic chart tells us the primary “oxidation state” state” P5: In one of its compounds with oxygen, iron (Fe) has an oxidation state of +3. Which of the following chemical formulas depicts this compound? a. FeO2 b. Fe3O2 c. Fe2O3

Br-1

PS 110A Hatch Ch. 2222-26

Naming convention for salts The metal comes first with its name unchanged The nonmetal comes second, with the suffix “ide” appended Examples: Sodium chloride Potassium iodide

NaCl KI

PS 110A Hatch Ch. 2222-27

When Potassium (K) and Chlorine (Cl (Cl)) combine the resulting formula is

a) b) c) d) e)

KCl K2Cl KCl2 K2Cl3 K3Cl2

PS 110A Hatch Ch. 2222-28

P6: When Aluminum (Al) and Chlorine (Cl) Cl) combine the resulting formula is

PS 110A Hatch Ch. 2222-29

Formula? Aluminum Oxide?

a) b) c) d)

Al2Cl AlCl2 AlCl3 Al3Cl2

Al2O3 What about K+ and F-, Na+ and S2-, Fe3+ and O2-. PS 110A Hatch Ch. 2222-30

PS 110A Hatch Ch. 2222-31

Nomenclature

Nomenclature

If there is a possibility of more than one oxidation state indicate the oxidation state. FeO – iron (II) oxide Fe2O3 – iron (III) oxide

If there is a possibility of more than one oxidation state indicate the oxidation state. FeO – iron (II) oxide Fe2O3 – iron (III) oxide

PS 110A Hatch Ch. 2222-32

PS 110A Hatch Ch. 2222-33

P7: When Calcium (Ca) and Phosphorus (P) combine the resulting formula is

Atoms With Multiple Valences Fe2+ iron II Cu+ copper I Au+ gold I Sn2+ tin II Pb2+ lead II Hg+ mercury I Cr2+ chromium II Mn2+ manganese II

Fe3+ iron III Cu2+ copper II Au3+ gold III Sn4+ tin IV Pb4+ lead IV Hg2+ mercury II Cr3+ chromium III Mn3+ manganese III PS 110A Hatch Ch. 2222-34

When Magnesium (Mg) and Sulfur (S) combine the resulting formula is

a) b) c) d) e)

a) b) c) d) e)

CaP Ca2P CaP2 Ca2P3 Ca3P2 PS 110A Hatch Ch. 2222-35

Flourine combines with the release of heat and energy

MgS Mg2S MgS2 Mg2S3 Mg3S2 PS 110A Hatch Ch. 2222-36

PS 110A Hatch Ch. 2222-37

Ionic vrs. vrs. Metal Bonding Metallic Bonding Ionic bonding Bonds arise from electrostatic interactions

True or False

True or False

Attractions extend True or False over large distances

True or False

Charge carriers are mobile

True or False

True or False

PS 110A Hatch Ch. 2222-38

Transition Metals? They don’t follow the Octet Rule. The d electrons invalidate the rule. Manganese forms ions with +2, +3, +4 charge. Would carbon like to gain or lose electrons? It turns out that it likes to share electrons in covalent bonds, which we’ll talk about next lecture. PS 110A Hatch Ch. 2222-39