Covalent BondingSkeleton Diagrams

Edward A. Mottel

Department of Chemistry

Rose-Hulman Institute of Technology

04/19/23

Only the noble gases have exactly thecorrect number of electrons to filltheir outermost s and p orbitals.

All other atoms have to lose, gain or shareelectrons to attain the stability

associatedwith the noble gases.

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Atoms which gain or lose electrons are called ions.An ionic bond is the electrostatic attraction

that holds ions together.

A covalent bond is the sharing of electronsbetween two atoms.

Atoms share electrons to attainthe electronic configuration and stability

of a noble gas.

Each atom has a tendency to form a certain numberof bonds in stable, neutral compounds.

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Bonding Tendencies

H 1 H H -•

Li 1 Li Li -•

Be 2 Be - Be -••

B 3 B •••

- B -

BondsKernal

diagramSkeletondiagram

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Bonding Tendencies

C •••

•C 4 - C -

N 3•••N

• •

- N -

O 2 - O -O••

• •• •

F 1 F -F •• •

• •••

BondsKernal

diagramSkeletondiagram

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Skeleton Diagrams

These atoms are neutral in charge. Only outer shell (valence) electrons are

included. Each atom tends to form a specific number of

bonds when it forms a molecule. Often, an unique atom is at the center of the

structure.

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hydrogenfluoride

H – F – represents a single bond

between two atoms

carbondioxide

O=C=O= represents a double bond

(i.e., two bonds) between thesame two atoms

boronnitride B N

represents a triple bond(i.e., three bonds) betweenthe same two atoms

berylliumoxide

Be=O

Skeleton Diagrams of Molecules

Skeleton diagrams indicatewhich atoms are bound together.

Skeleton diagrams providesome information aboutthe strength of the bond.

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Skeleton Diagrams of Molecules

N

H

H H ammoniaC

H

H H

H

methane

OH Hwater

CH H

Oformaldehyde

H-N-H bond angle107°

H-C-H bond angle109.5°

H-O-H bond angle104.5°

H-C-H bond angle~120°

Skeleton diagrams do not indicate bond angles!

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Bond Order Bond Energy

fluorinegas

(difluorine)F – F 1 155 kJ·mol–1

oxygengas

(dioxygen)O = O 2 495 kJ·mol–1

nitrogengas

(dinitrogen)N N 3 941 kJ·mol–1

Skeleton Diagrams of Molecules

Which gas is the most reactive?

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Pairs Activity

A pair of people will work on one problem:

• One person is responsible for writing all the information.

• The other person is responsible for saying what should be written.

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On a card or a piece of paper

Write each sequential step necessary to draw a skeleton diagram.

Number each step. Amend and update the list.

• Either person may do this.

Draw the skeleton diagram of acetic acid, CH3COOH

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Isomers

An isomer is a compound with the same molecular formula, but different structure.• The atoms are linked differently together.

Draw the skeleton diagram of an isomer of acetic acid, CH3COOH

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Isomers of C2H4O2

methyl formate

acetic acid

O HC

H

H

H

C

O

C

O

O HC

H

H

H

O HCH

H

H

C

O glycolaldehyde

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Unstable Isomers of C2H4O2

Small ring structures(containing 3 or 4 atomsin the ring) are eitherunstable or very reactive

C

H

H O

O C H

H

H CC

H

O

H

H

O

O HC

H

H CO

HC O

O C

CC

O O

C CO

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Sodium Acetate

Acetic acid reacts with sodium hydroxide to form sodium acetate and water.

Draw the skeleton diagram of sodium acetate.

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Draw the skeleton diagrams for

boric acid, H3BO3

aluminum hydroxide

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H3BO3 and Al(OH)3

OH O HB

O

H

OH O HAl

O

H

boric acid

aluminum hydroxide

Compare the Structures of Boric Acidand Aluminum Hydroxide

Both have similarskeleton diagrams,

but differentchemical properties.

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Compare their position on the periodic table.The Periodic StaircaseSeparates Metals and Nonmetals

Boron is a metalloid or semi-metal,whereas aluminum is metallic.

nonmetals

metals

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Compare the Structures of Boric Acid and Aluminum Hydroxide

Both have amphoteric character.

OH O HB

O

H

OH O HAl

O

H

Nonmetal oxidesare acidic

H

Metal oxidesare basic

O H

Which bond might breakto show each chemical character?

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Skeleton Diagrams

The skeleton bonding approach works for many molecules;• however, it fails to explain the bonding in

some simple molecules and ions.

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Skeleton Diagrams

What is the skeleton diagram for• carbon monoxide• ammonium ion• cyanide ion

Which atom(s) in each structure breaks the skeleton bonding rules?

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Skeleton Diagram Failures

C O C Oor

N

H

H H

H

+

N

H

H H

H

+

or

C NC N or

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Types of Bonds Formed

N N PP

PP

O O

SSSS

S SSS

Lighter members of a familyoften form multiple bonds

Heavier members favoradditional single bonds.

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Heavier Members of a Familytend to form single bonds

C OO

carbon dioxide Si

O O

Si

O

Si

O

OSi

O

O

Si

O

O

silicon dioxidequartz, glass, sand

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Bonding Theories

Ionic Model Skeleton Diagrams

• Identifies how atoms are linked together• Fails to describe the bonding in ions and

certain molecules (e.g., CO, NH4+, CN–)

• Fails to explain the geometry of molecules

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