Molecules and Ions

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MoleculesTwo or more atoms of the same or different elements, covalently bonded together.

Molecules are discrete structures, and their formulas represent each atom present in the molecule.

Pentane, C5H12

Covalent Network Substances

Covalent network substances have covalently bonded atoms, but do not have discrete formulas.

Why Not??

Graphene – carbon allotrope

IonsIons

Cation: A positive ionMg2+, NH4

+

Anion: A negative ionCl-, SO4

2-

Ionic Bonding: Force of attraction between oppositely charged ions.

Ionic compounds form crystals, so their formulas are written empirically (lowest whole number ratio of ions).

Predicting Ionic Charges

Group 1: Lose 1 electron to form 1+ ions H+ Li+ Na+ K+ Rb+ Cs+

Predicting Ionic Charges

Group 2: Loses 2 electrons to form 2+ ions

Be2+ Mg2+ Ca2+ Sr2+ Ba2+

Predicting Ionic ChargesGroup 13: Loses 3 electrons to form 3+ ions

B3+ Al3+ Ga3+

Predicting Ionic ChargesGroup 14: Loses 4 electrons or gains 4 electrons

Caution! C22- and C4-

are both called carbide

Predicting Ionic ChargesGroup 15: Gains 3 electrons to form 3- ions

N3-

P3-

As3-

NitridePhosphide

Arsenide

Predicting Ionic ChargesGroup 16: Gains 2 electrons to form 2- ions

O2-

S2-

Se2-

Oxide

SulfideSelenide

Predicting Ionic ChargesGroup 17: Gains 1 electron to form 1- ions

F1-

Cl1-

Br1-

Fluoride

Chloride

Bromide

I1- Iodide

Predicting Ionic ChargesGroup 18: Stable Noble gases do not form ions!

Predicting Ionic ChargesGroups 3 - 12: Many transition metals have more than one possible oxidation state.

Iron(II) = Fe2+ Iron(III) = Fe3+

Predicting Ionic ChargesGroups 3 - 12: Some transition metals have only one possible oxidation state. Zinc = Zn2+ Silver = Ag+

Writing Ionic Compound Formulas

Example: Barium nitrate

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

Ba2+ NO3-

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.

Not balanced

( )

2

Writing Ionic Compound Formulas

Example: Ammonium sulfate

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

NH4+ SO4

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.

Not balanced

( )2

Writing Ionic Compound Formulas

Example: Iron(III) chloride

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

Fe3+ Cl-

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.

Not balanced

3

Writing Ionic Compound Formulas

Example: Aluminum sulfide

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

Al3+ S2-

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.

Not balanced

2 3

Writing Ionic Compound Formulas

Example: Magnesium carbonate

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

Mg2

+CO3

2-

2. Check to see if charges are balanced.

They are balanced

Writing Ionic Compound Formulas

Example: Zinc hydroxide

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

Zn2+ OH-

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.

Not balanced

( )2

Writing Ionic Compound Formulas

Example: Aluminum phosphate

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

Al3+ PO43-

2. Check to see if charges are balanced.

They ARE balanced

Naming Ionic CompoundsNaming Ionic CompoundsCation first, then anion

Monatomic cation = name of the element

Ca2+ = calcium ion

Monatomic anion = root + -ideCl- = chloride

CaCl2 = calcium chloride

Naming Ionic CompoundsNaming Ionic Compounds

some metal forms more than one cation

use Roman numeral in name

PbCl2

Pb2+ is cation

PbCl2 = lead(II) chloride

Metals with multiple oxidation states

Binary Molecular CompoundsBinary Molecular Compounds

Compounds between two nonmetals First element in the formula is named

first. Keeps its element name Gets a prefix if there is a subscript

on it Second element is named second

Use the root of the element name plus the -ide suffix

Always use a prefix on the second element

List of Prefixes

1 = mon(o) 2 = di 3 = tri 4 = tetra 5 = penta 6 = hexa 7 = hepta 8 = octa 9 = nona 10 = deka

Naming Binary Compounds

Naming Binary Compounds

P2O5 =

CO2 =

CO =

N2O =

diphosphorus pentoxide

carbon dioxide

carbon monoxide

dinitrogen monoxide

Practice – Write the FormulaCompound Name Compound Formula

Carbon dioxide

Carbon monoxide

Diphosphorus pentoxide

Dinitrogen monoxide

Silicon dioxide

Carbon tetrabromide

Sulfur dioxide

Phosphorus pentabromide

Iodine trichloride

Nitrogen triiodide

Dinitrogen trioxide

Check next slide for answers

Answers – Write the FormulaCompound Name Compound Formula

Carbon dioxide CO2

Carbon monoxide CO

Diphosphorus pentoxide P2O5

Dinitrogen monoxide N2O

Silicon dioxide SiO2

Carbon tetrabromide CBr4

Sulfur dioxide SO2

Phosphorus pentabromide PBr5

Iodine trichloride ICl3

Nitrogen triiodide NI3

Dinitrogen trioxide N2O3

Practice – Name the Compounds

Compound Formula

Compound Name

N2O4

SO3

NO

NO2

As2O5

PCl3

CCl4

H2O

SeF6

Check next slide for answers

Answers – Name the Compounds

Compound Formula

Compound Name

N2O4 dinitrogen tetroxide

SO3 sulfur trioxide

NO nitrogen monoxide

NO2 nitrogen dioxide

As2O5 diarsenic pentoxide

PCl3 phosphorus trichloride

CCl4 carbon tetrachloride

H2O dinitrogen monoxide

SeF6 selenium hexafluoride