Covalent Bonding Skeleton Diagrams Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology

7/13/2015 Only the noble gases have exactly the correct number of electrons to fill their outermost s and p orbitals. All other atoms have to lose, gain or share electrons to attain the stability associated with the noble gases.

7/13/2015 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 electrons between two atoms. Atoms share electrons to attain the electronic configuration and stability of a noble gas. Each atom has a tendency to form a certain number of bonds in stable, neutral compounds.

7/13/2015 Bonding Tendencies H1HH - Li1 Li - Be2 - Be - B3 B - B - Bonds Kernal diagram Skeleton diagram

7/13/2015 Bonding Tendencies C C4 - C - N3 N - N - O2- O - O F1F - F Bonds Kernal diagram Skeleton diagram

7/13/2015 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.

7/13/2015 hydrogen fluoride H – F – represents a single bond between two atoms carbon dioxide O=C=O = represents a double bond (i.e., two bonds) between the same two atoms boron nitride B  N  represents a triple bond (i.e., three bonds) between the same two atoms beryllium oxide Be=O Skeleton Diagrams of Molecules Skeleton diagrams indicate which atoms are bound together. Skeleton diagrams provide some information about the strength of the bond.

7/13/2015 Skeleton Diagrams of Molecules N H HH ammonia C H HH H methane O HH water C HH O formaldehyde H-N-H bond angle 107° H-C-H bond angle 109.5° H-O-H bond angle 104.5° H-C-H bond angle ~120° Skeleton diagrams do not indicate bond angles!

7/13/2015 Bond OrderBond Energy fluorine gas (difluorine) F – F 1155 kJ·mol – 1 oxygen gas ( dioxygen) O = O2495 kJ·mol – 1 nitrogen gas (dinitrogen) N   N 3941 kJ·mol – 1 Skeleton Diagrams of Molecules Which gas is the most reactive?

7/13/2015 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.

7/13/2015 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, CH 3 COOH

7/13/2015 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, CH 3 COOH

7/13/2015 Isomers of C 2 H 4 O 2 methyl formate acetic acid O H C H H H C O C O O H C H H H O H C H H H C O glycolaldehyde

7/13/2015 Unstable Isomers of C 2 H 4 O 2 Small ring structures (containing 3 or 4 atoms in the ring) are either unstable or very reactive C H HO O C H H H C C H O H H O O H C H H C O H C O O C C C OO CC O

7/13/2015 Sodium Acetate  Acetic acid reacts with sodium hydroxide to form sodium acetate and water. Draw the skeleton diagram of sodium acetate.

7/13/2015 Draw the skeleton diagrams for  boric acid, H 3 BO 3  aluminum hydroxide

7/13/2015 H 3 BO 3 and Al(OH) 3 O H O H B O H O H O H Al O H boric acid aluminum hydroxide Compare the Structures of Boric Acid and Aluminum Hydroxide Both have similar skeleton diagrams, but different chemical properties.

7/13/2015 Compare their position on the periodic table. The Periodic Staircase Separates Metals and Nonmetals Boron is a metalloid or semi-metal, whereas aluminum is metallic. nonmetals metals

7/13/2015 Compare the Structures of Boric Acid and Aluminum Hydroxide Both have amphoteric character. O H O H B O H O H O H Al O H Nonmetal oxides are acidic H Metal oxides are basic O H Which bond might break to show each chemical character?

7/13/2015 Skeleton Diagrams  The skeleton bonding approach works for many molecules; however, it fails to explain the bonding in some simple molecules and ions.

7/13/2015 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?

7/13/2015 Skeleton Diagram Failures C O C O or N H HH H + N H HH H + C N C N

7/13/2015 Types of Bonds Formed N N P P P P O O S S S S S S S S Lighter members of a family often form multiple bonds Heavier members favor additional single bonds.

7/13/2015 Heavier Members of a Family tend to form single bonds C O O carbon dioxide Si O O O O O O O O O silicon dioxide quartz, glass, sand

7/13/2015 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, NH 4 +, CN – ) Fails to explain the geometry of molecules

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