bonding revisited few things are truly black-or-white
TRANSCRIPT
Bonding RevisitedFew things are truly black-or-white
Previous PicturesIonic: charges, no shared electrons.Covalent: completely shared
electrons
But just like siblings, not all elements share well…
New Picture
Bonding is more like a spectrum, which ranges from perfectly shared, to completely unshared.
Many compounds have covalent bonds that are unevenly shared.
New Picture
If the electrons aren’t shared evenly, then the atoms aren’t exactly neutral.
But if they’re not all the way over, they’re not exactly +1 and -1 either.
Atom A is partially positive (δ+) and atom B is partially negative (δ-)
ElectronegativityElectronegativity: how strongly an atom pulls on shared electrons.
There are values you can look up, but we’ll mostly just use categories:
ElectronegativityElectronegativity: how strongly an atom pulls on shared electrons.
There are values you can look up, but we’ll mostly just use categories:
The King: Fluorine.
ElectronegativityElectronegativity: how strongly an atom pulls on shared electrons.
There are values you can look up, but we’ll mostly just use categories:
The King: Fluorine.Very strong: Oxygen, Nitrogen, Chlorine
ElectronegativityElectronegativity: how strongly an atom pulls on shared electrons.
There are values you can look up, but we’ll mostly just use categories:
The King: Fluorine.Very strong: Oxygen, Nitrogen, ChlorinePretty strong: Phosphorous, Sulfur, Bromine, Iodine
ElectronegativityElectronegativity: how strongly an atom pulls on shared electrons.
There are values you can look up, but we’ll mostly just use categories:
The King: Fluorine.Very strong: Oxygen, Nitrogen, ChlorinePretty strong: Phosphorous, Sulfur, Bromine, IodineWimpy: Carbon, Hydrogen, Silicon
ElectronegativityElectronegativity: how strongly an atom pulls on shared electrons.
There are values you can look up, but we’ll mostly just use categories:
The King: Fluorine.Very strong: Oxygen, Nitrogen, ChlorinePretty strong: Phosphorous, Sulfur, Bromine, IodineWimpy: Carbon, Hydrogen, Silicon Super weak: metals
Tug-of-WarWhether a bond is non-polar, polar, or covalent depends on the electronegativity of the atoms compared:
Same strength: nobody wins—perfectly covalent
(The only difference strength makes is how strong the bond is—two elements pulling hard makes it weaker than two pulling weakly)
Tug-of-WarWhether a bond is non-polar, polar, or covalent depends on the electronegativity of the atoms compared:
Similar strengths: uneven distribution—polar covalent
The more electronegative element will have a partial negative, and the less partially positive.
Tug-of-WarWhether a bond is non-polar, polar, or covalent depends on the electronegativity of the atoms compared:
Very different strengths: Completely stole the rope—ionic
The more electronegative element just takes the electrons—becomes negative. This basically only happens with metal compounds
(hence our rule about metal compounds being ionic)
Drawing the PolarityThe polarity is either shown with the partial charge symbols (δ+ and δ-) or with arrows:
C—O Cl—H
Arrow’s plus-sign-looking end goes with the partially positive atom, and point with the partially negative end.
Sometimes the lengths of the arrow are used to show when one is more or less polar.
How Bonds are MadeTo make a bond, electrons have to overlap. There are two ways for this to happen:
1. Directly overlapping: sigma (σ) bond
The first bond made between any two atoms is always a sigma bond
How Bonds are MadeTo make a bond, electrons have to overlap. There are two ways for this to happen:
2. Once the space in between is used up, you have to find another way: pi (π) bonds
Made with parallel p orbitals
These are the second and third bonds of double/triple bonds.
How Bonds are Made H—CN
Sigma bondSigma bond and two pi bonds
SummaryMany bonds aren’t perfectly shared. These are polar (have partial charges)
Electronegativity is how much atoms pull on shared electrons
Polar bonds come from uneven electronegativity
Bonds can be made two ways:Direct overlap (sigma)Aligned p orbitals (pi)