Chapter 11: Molecular Compounds

Covalent Bonds

When two nonmetals interact with one another, they can bond without forming ions. 

• Instead of transferring electrons from one atom to another, they transfer valence electrons

Single Bond

Only one pair of electrons is shared

• Single bonds are represented by one line

• Ex: when two chlorine atoms come in contact with one another they share a pair of electrons 

Double Bond

Sharing two pairs of electrons to be “happy”

• Ex: each oxygen atom has 6 valence electrons

  • When two come together the must share two pairs of electrons 

Triple Bond

Nitrogen atoms have five valence electrons, share three pairs of electrons

Two types of electron pairs: pairs that are shared between atoms that are not

1. Bonding Pairs

2. Lone Pairs 

Valence Electrons are shared in Covalent Bonds therefore…

• There is some overlap between electron clouds

• The more overlap between the clouds, the more stable the bond

  • Factor that limits how much overlap there can be: the repulsion of positively charged nuclei

Potential Energy Diagram: 

• X-axis: distance between nuclei

• Y-axis: potential energy of the two atoms 

• Low energy = stability 

• High energy = instability

When atoms are far apart…

They have no interaction with each other

What is an atom’s baseline?

• Having no interaction with each other is the baseline 

  • It is neither high or low energy → its neutral 

As atoms approach each other…

• The electron clouds begin to overlap and the sharing of electrons begins

• Each atom is somewhat satisfied with this position as their octet begins to fill

When electron clouds overlap…

•  the more sharing occurs and therefore the more stable it becomes

  • HOWEVER: as the clouds overlap more the nuclei get closer and closer together 

    • The repulsion on the nuclei gets stronger and stronger

When nuclei are close…

The potential energy is very high and the arrangement becomes unstable

Where is the best spot on a graph for atoms?

The atoms must strike a balance → the ideal spot is at the low point of the graph (point C) 

Electron Domain

• a bond or lone pair

  • Single, double, or triple bonds refer to one domain

  • Electron domains are negatively charged and therefore repel one another 

  • They are all connected by a central atom so they arrange themselves so they are far away

  • Mutual repulsion is based on valence shell electron pair repulsion theory (VSEPR)

  • two electron domains, central, atom they will repel each other until they are on opposite side

Linear

Domains are 180 degrees apart

Trigonal Planar

• Domains are 120 degrees apart

• Molecular Geometry 

  • No lone pairs: trigonal planar 

  • Lone pair: bent 

• Lone pairs are drawn on the central atom in teardrop clouds 

Tetrahedral

• 109.5 degrees apart

• Molecular Geometry

  • No lone pairs: tetrahedral

  • Lone pair: trigonal pyramidal 

  • Two lone pairs: bent

Molecular Geometry

Once actual atoms and lone pairs are put on the electron domains

• The molecular geometry is determined on the arrangement of the atoms 

Bond Polarity

• In every chemical bond, the atoms on either end are pulling at the bonding electrons 

• Atoms with a higher electronegativity can pull harder than atoms with a lower one 

Ionic Bond (0 - 0.5)

• If one atom is much more electronegative than the other then it pulls the electron away completely 

• The more electronegative atom gains the electron and becomes a negative ion

• The less electronegative atom loses the electron and becomes a positive ion

Polar Covalent (0.5 - 1.7)

• If one atom is a little bit stronger, the bonding electrons are held closer to the more en atom

• b/c the electrons are slightly closer to the more en atom, it has a partially negative charge 

• Likewise the less en atom only has a partially positive charge 

Nonpolar Covalent (Over 1.7)

If both atoms have the same electronegativity, they pull equally 

Molecular Polarity

• Polarity can be represented through arrows pointing to the more en atom 

• The back end of the arrow is a plus sign to indicate it is more positive on that side 

• All the bond polarities in a molecule combine to form overall molecular polarity