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Ch. 4: Compounds and Their Bonds

Chem. 20

El Camino College

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Octet Rule

8 e-s is a magic number Main Group elements (except H and He)

will give, take, or borrow electrons to reach 8 electrons in the outermost shell

Noble Gases (except He) have 8 electrons in the outer shell, so they don’t give or take electrons

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Cations: Positive Ions

Atoms are neutral Ions have a charge Cations are positive, Anions are negative Metals lose e-s easily to form cations When electrons are lost, the particle left

over has a positive charge.

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Main Group. Cations: Positive Ions

Ex. Sodium atom has one valence electron. When Na loses 1 e-, a cation with a positive charge forms

The name of Na+ is sodium ion Note, for a +1 charge, just show +.

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Main Group. Cations: Positive Ions

Ex. Mg atom has 2 valence electrons When Mg loses 2 electrons, a cation with a

+2 charge forms The name of Mg2+ is magnesium ion Note, show the number, then the charge.

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Anions: Negative Ions Nonmetals gain electrons easily to form

anions When electrons are gained, the particle has

a negative charge Example: When Cl gains 1 e-, an anion with

-1 charge forms The name of Cl- is chloride ion.

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Anions: Negative Ions

Ex. How many valence e-s does N have? 5 How many e-s will N gain to reach 8? 3 The formula for nitride ion is N3-

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Names of Ions

For metal ions in groups. 1, 2, and 3, the name is the metal plus the word “ion”

K+ is potassium ion Ca2+ is calcium ion What is the name of Al3+? aluminum ion

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Names of anions

For anions (nonmetal ions), the name is the nonmetal in ide form, plus the word “ion”

F- is fluoride ion O2- is oxide ion What is the name of S2-? sulfide ion

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Name These

Li Li+

P3-

P Ba2+

Ba

lithium lithium ion phosphide ion phosphorus barium ion barium

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Charges from Group number

Gp 1 (1A) metals form + ions Gp 2 (2A) metals form 2+ ions Gp 13 (3A) metals form 3+ ions

Gp 15 (5A) nonmetals form 3- ions Gp 16 (6A) nonmetals form 2- ions Gp 17 (7A) nonmetals form - ions

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Ionic Compounds

An ionic bond occurs when one atom gives electrons to another

Compounds always have zero charge.

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Predicting Ionic Formulas Determine the charge of each ion Combine ions to get zero charge overall Use the lowest numbers possible Ex. A compound contains sodium ions and sulfide ions.

Write the formula. Sodium ion is Na+, sulfide ion is S2-

It will take 2 Na+ ions to cancel the charge in one S2- ion The formula is Na2S.

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Write the Formulascompound contains

potassium ions, iodide ions chloride ions, calcium ions aluminum ions, nitride ions beryllium ions, fluoride ions sulfide ions, lithium ions aluminum ions, oxide ions

KI CaCl2 AlN BeF2

Li2S

Al2O3

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Naming Ionic Compounds The 1st word is the cation name (metal ion) The 2nd word is the anion name Never use the word “ion” in a name

LiBr MgF2

CaS Ca3P2

K2O

AlCl3

lithium bromide magnesium fluoride calcium sulfide calcium phosphide potassium oxide aluminum chloride

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Transition Metal Ions Some transition metals may form many cations Know these transition metal ions

Cr2+, Cr3+ chromium(II) ion, chromium(III) ionFe2+, Fe3+ iron(II) ion, iron(III) ionCu+, Cu2+ copper(I) ion, copper(II) ionSn2+, Sn4+ tin(II) ion, tin(IV) ionPb2+, Pb4+ lead(II) ion, lead(IV) ion

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Transition Metal Ions Chromium can form two ions: Cr2+, Cr3+

To name, use a Roman numeral in parentheses and the word “ion” The name of Cr3+ is chromium(III) ion What is the name of Pb4+? lead(IV) ion (note--parentheses are only for elements that form

more than one ion such as Cr, Fe, Cu, Sn, Pb) What is the name of Ag? silver What is the name of Ag+? silver ion

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Transition Metals in Compounds

When a compound contains a transition metal with variable charge, you must determine what the charge is

Ex. Name FeCl2 Is that Fe2+ or Fe3+? Since chloride ion is Cl- and there are 2 of them, this must

be iron(II) ion Iron(II) chloride Write the formula for iron(III) bromide FeBr3

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Examples

Name CuO, Cu2O, Fe2S3, FeO, PbS, PbS2, AgCl copper(II) oxide copper(I) oxide iron(III) sulfide iron(II) oxide lead(II) sulfide lead(IV) sulfide silver chloride

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Formulas

chromium(III) bromide, chromium(II) sulfide, zinc oxide, tin(II) nitride, tin(IV) nitride, tin(II) oxide

CrBr3

CrS ZnO Sn3N2

Sn3N4

SnO

Jumbo Practice 1

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Polyatomic Ions

Polyatomic ions are ions that contain more than 1 atom Never change the numbers inside or the charge of a

polyatomic ion If you need more than one polyatomic ion, use

parentheses.

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OH-

Hydroxide ion is OH-

To write the formula of sodium hydroxide Sodium ion is Na+

Hydroxide ion is OH-

NaOH

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OH-

To write the formula of calcium hydroxide Calcium ion is Ca2+

Hydroxide ion is OH-

Ca(OH)2

Note: Writing CaO2H2 or CaOH2 is incorrect

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Other Polyatomic Ions

Nitrate ion NO3-, sulfate ion SO4

2-, phosphate ion PO43-

Write the formulas for sodium nitrate, sodium sulfate, and sodium phosphate NaNO3

Na2SO4

Na3PO4

Write the formulas for calcium nitrate, calcium sulfate, and calcium phosphate Ca(NO3)2

CaSO4

Ca3(PO4)2

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Other Polyatomic Ions

Be careful with similar sounding ions sulfate ion SO4

2-, sulfite ion SO32-, sulfide ion S2-

hydrogen sulfate ion HSO4-

carbonate ion CO32-

hydrogen carbonate ion HCO3-

acetate ion C2H3O2-

ammonium ion NH4+

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Examples

Name CuNO3, Cu2SO3, ZnSO3, Sn(C2H3O2)4, KHCO3

copper(I) nitrate copper(I) sulfite zinc sulfite tin(IV) acetate potassium hydrogen carbonate

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Formulas

chromium(III) hydrogen sulfate, iron(II) phosphate, zinc hydroxide, tin(II) carbonate, ammonium acetate

Cr(HSO4)3

Fe3(PO4)2

Zn(OH)2

SnCO3

NH4C2H3O2

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Ionic vs. Covalent

All the compounds we’ve looked at so far are ionic

The cation of an ionic compound is a metal ion or ammonium ion

The anion of an ionic compound is a nonmetal ion or polyatomic ion

In ionic compounds, e-s are given from one atom to another.

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Ionic vs. Covalent

Covalent compounds are made of 2 nonmetals

In covalent compounds, e-s are shared (not given away)

Covalent compounds are called molecules Ionic compounds are never called

molecules.

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Diatomic Molecules are Formed by Covalent Bonds

H2 hydrogen

N2 nitrogen

O2 oxygen

F2 fluorine

Cl2 chlorine

Br2 bromine

I2 iodine

•There are 7 elements that form diatomic molecules•Formulas for these elements are always shown with subscript “2”

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Fig. 6-1, p. 137

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Examples• Write the formulas

• gold

• iodine• helium• nitrogen• oxygen• potassium

Au

I2

He

N2

O2

K

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Naming Compounds

• A compound is 2 or more elements bonded together

• The rules for naming covalent (nonmetal-nonmetal) compounds are different than the rules for ionic (metal-nonmetal) compounds

• Always check the periodic table to decide which rules to use.

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Molecular Compounds (Nonmetal-Nonmetal)

• We’ll only be naming binary molecular (nonmetal-nonmetal) compounds (made of 2 elements)

• The 1st word is the name of the 1st element• The 2nd word is the name of the 2nd element in

“ide” form• Use a prefix for the number.

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Prefixes in Molecular Compounds

• One: mono- • Two: di-• Three: tri-• Four: tetra-• Five: penta-

• Six: hexa-• Seven: hepta-• Eight: octa-• Nine: nona-• Ten: deca-

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Putting it all Together

• CO2 is a molecular compound

• The 1st word is the name of the 1st element: carbon (the prefix mono is omitted in the 1st word)

• The 2nd word is the 2nd element in “ide” form, with the prefix “di”

• The name is carbon dioxide.

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Examples

• Name these: NF3, S2Br4, CCl4, N2

• nitrogen trifluoride• disulfur tetrabromide• carbon tetrachloride• nitrogen

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Awkward Vowel Combinations

• When the combinations “ao” or “oo” appear, remove the first awkward vowel

• Example: SiO4 is silicon tetroxide

• Name P2O5, I2O, and SI2

• diphosphorus pentoxide• diiodine monoxide• sulfur diiodide

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Water and Ammonia

The name of H2O is water

The name of NH3 is ammonia.

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Sharing electrons between Different Nonmetals

Most nonmetals share electrons to reach 8 electrons

Except: H reaches 2e-s, B reaches 6 e-s e- dot formulas show how e-s are shared

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e- Dot Formulas

Electrons in covalent compounds exist as bonding pairs or as lone pairs

A bonding pair is 2 elctrons shared between 2 atoms A lone pair is a pair of electrons around the outside

of an atom

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e- Dot Formulas

Use this guide to help you connect the dots H gets 1 bond B gets 3 bonds C, Si get 4 bonds N, P get 3 bonds and 1 lone pair O, S get 2 bonds and 2 lone pairs F, Cl, Br, I get 1 bond and 3 lone pairs

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e- Dot Formulas

:: :

H B NC

Si:

P:

O::

S

::X

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e- Dot Formulas

X represents any halogen. Halogens get 1 bond and 3 lone pairs.

Halogens never get 2 bonds.

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Examples

Draw these molecules. Be careful about how many bonds and lone pairs each atom prefers to have.

BI3 SCl2 CH4

Cl

S

Cl

::

::

::: :

C

H

HH

H

:

B

I

II ::

::

::

: :

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Examples

Draw these molecules. Be careful about how many bonds and lone pairs each atom prefers to have.

BH3 H2O PCl3

B

H

HH

::

H

O

H

:

::

::

::

:

P

ClCl

Cl

::

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Double and Triple Bonds are also possible

Draw CO2 (C is in the center)

Draw CH2O (all atoms attached to C)

Draw N2

O C O

O

C

HH

::

N N: :

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VSEPR: Valence Shell Electron Pair Repulsion Theory

VSEPR Theory predicts the shapes of molecules

e- sets (bonds or lone pairs) get as far away from each other as possible

Geometry is determined around one atom at a time.

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VSEPR

One “set” is a lone pair or a single bond or a double bond or a triple bond

A single, double, or triple bond connects to a bonded atom (BA).

A lone pair (LP) is not bonded to anything

Molecular shapes use bonded atoms (BA) only.

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Ex: How many sets are around each indicated atom? How many bonded atoms and how many lone pairs?

Sets BA LP

a. 4 4 0

b. 3 3 0

c. 3 1 2

d. 4 3 1

e. 4 4 0

f. 2 2 0

g. 2 2 0

h. 4 2 2

CC

NC

C

C

O

H

H

H

H

O

H

H H

ab

c

d

e fg

h

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Fig. 12-1, p. 325

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Atoms with 2 Sets When an atom has 2 sets around it, e- repulsion

pushes the sets as far apart as possible from each other

The two sets will be 180o apart

The molecular shape is linear

O C O

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Fig. 12-2a, p. 325

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Atoms with 3 Sets When an atom has 3 sets around it, the 3 sets

will be 120o apart due to e- repulsion. When the 3 sets are bonded atoms, the

molecular shape is trigonal planar When 2 sets are BA and 1 set is an LP, the

molecular shape is bent.

B

H

HH

:

O

N

O:

:: :

:

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Fig. 12-2b, p. 325

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Atoms with 4 Sets When an atom has 4 sets around it, the 4 sets

will be 109.5o apart When the 4 sets are bonded atoms, the

molecular shape is tetrahedral When 3 sets are BA and 1 set is an LP, the

molecular shape is trigonal pyramidal When 2 sets are BA and 2 sets are LP, the

molecular shape is bent.

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Fig. 12-2c, p. 325

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Atoms with 4 Sets

In CH4, the shape is tetrahedral

In NH3, the shape is trigonal pyramidal

In H2O, the shape is bent

C

H

HH

H H

N

H

H

:

H

O

H

::

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Fig. 12-5, p. 328

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# e- sets

molecular shapebond angle

2 2BA: linear 180o

33BA: trigonal planar 120o

2BA, 1LP: bent <120o

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4BA: tetrahedral 109.5o

3BA, 1LP: trigonal pyramidal <109.5o

2BA, 2LP: bent <109.5o

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Electronegativity & Bond Polarity

Electronegativity is the ability to attract e-s The most electronegative element is F The closer on the periodic table to F, the

higher the electronegativity Electronegative elements “pull” e- density

towards themselves.

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Bond Polarity

You can show bond polarity in two ways, with partial charges or with polarity arrows

:: :H-F

:: :H-F

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Example For BCl3, draw partial charges on all the

atoms

For BCl3, draw polarity arrows next to all the bonds

Cl

B

ClCl

:

::

:

:

:

: ::

Cl

B

ClCl

:

::

::

:

: ::

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Electronegativity & Bond Polarity

There are 2 types of covalent bonds nonpolar covalent bonds polar covalent bonds

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Electronegativity & Bond Polarity

In a nonpolar covalent bond, the 2 nonmetal atoms are the same

In a polar covalent bond, the 2 nonmetal atoms are different.

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Electronegativity & Bond Polarity

Ex. Electronegativities (H=2.1, Cl=3.0) Is an H-H bond nonpolar covalent or

polar covalent? Is a Cl-Cl bond nonpolar covalent or

polar covalent? Is an H-Cl bond nonpolar covalent or

polar covalent?

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Polarity of Molecules

You determined whether a bond was polar covalent or nonpolar covalent

Using that information and the correct shapes, you can determine whether a whole molecule is polar or nonpolar.

Remember, polarity of bonds and polarity of molecules are different

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Review: Polarity of Bonds

Draw BF3 and NF3 in the correct shapes. Draw a polarity arrow next to each bond.

:

B

F

FF :::

:

::

: : :

::

F

N

F

F :

::

:

:: :

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Polarity of Molecules

To determine if a molecule is polar or nonpolar, add the polarity arrows.

The polarity arrows cancel (have no overall pull) in a nonpolar molecule

The polarity arrows demonstrate an overall pull in one direction in a polar molecule

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Polarity of Molecules Determine whether BF3 and NF3 are polar

or nonpolar.

:

B

F

FF ::

::

::

: : :

::

F

N

F

F :

::

::

: :

In BF3, the polarity arrows cancel. The molecule is nonpolar.In NF3, the arrows don’t cancel. There is overall pull and the molecule is polar.

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Notes on Polarity of Molecules

You must draw the structure in the correct shape to get polarity of molecules correct

Polarity of bonds is different than polarity of molecules

BF3 has polar covalent bonds, but BF3 is a nonpolar molecule

NF3 has polar covalent bonds and is a polar molecule.

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Notes on Polarity of Molecules

The size of the polarity arrow represents the relative difference in electronegativity

A B-F bond would have a bigger polarity arrow than a B-Cl bond

When polarity arrows cancel, both the size and direction are taken into account.

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Examples Draw CHCl3 and CCl4

What are the approx. bond angles? Which molecule contains nonpolar covalent

bonds? Which molecule contains polar covalent bonds? Which molecule is polar?

Cl

C

ClCl

Cl:

::

:

:

:

:

::

::

:

H

C

ClCl

Cl:

::

:

::

:

::

109.5o

neitherboth

CHCl3

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Fig. 12-10, p. 335

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Examples: Draw Each One and Answer the Questions

H2O CH3NH2 PCl3 C2H4

a) Does it contain nonpolar covalent bonds?

b) Does it contain polar covalent bonds?

c) Is the molecule or ion polar or nonpolar overall?

a) a) a) a)

b) b) b) b)

c) c) c) c)

:

::

Cl

P

Cl

Cl :

:::

:: :

no

polaryes

H

O

H

::

no

polaryes

C

H

NH

H

HH

:

no

polar

yes

C C

H

HH

H

nonpolaryes

yes