The naming rules for double and triple bonds are almost the same, except there’s one thing that we need to add.
Double bonds take priority. There are two possible ways to number the carbon atoms. When we’re numbering we must choose the lowest number
Double bonds (alkenes) end in –ene
Triple bonds (alkynes) end in –yne
Multiple double bonds: As we all know more than one double bond can exist in a molecule. The only difference here is that we use the same multipliers inside the parent chain. EXAMPLE: (1,3 butadiene)
Here's a great video that teaches how to name Alkenes and Alkynes.
Organic chemistry is the study of carbon compounds. Carbons also form multiple covalent bonds. Carbon compounds can form chains, rings or branches. There are less than 100,000 non-organic compounds. Organic compounds number more than 17 million. The simplest organic compounds are made of carbon and hydrogen.
Saturated compounds have no double or triple bonds.
Compounds with only: single bonds -> Alkanes, double bonds -> Alkenes, triple bonds -> Alkynes
ISOMER: Two compounds with the same empirical formula
Example:
Name the alkane:
Nomenclature:
There are 3 categories of organic compound:
Straight
Cyclic chains
Aromatics
Straight Chains:
1.) Circle the longest continual chain and name this as the base chain. They can bend and twist.
2.) Number the base chains so side chains have the lowest possible numbers.
3.) Name each side chain using the "-yl" ending.
4.) Give each side chain the appropriate number.
->if there is more than one identical
side chain, number/labels are slightly different.
5.) List side chains alphabetically.
Intramolecular Bonds exist inside molecules, for example Ionic and Covalent bonds.
Intermolecular Bonds exist between molecules. The stronger the intermolecular bonds the higher the boiling point. Two types of intermolecular bonds are Van der Waals bonds and Hydrogen bonds
A. Van der Waals bonds are based on electron distribution. Van de Waals bonds can be categorized in two categories: a weak bond created by the London Dispersion Force (LDF) or dipole-dipole bonds.
1. London Dispersion Forces (LDF)
These are the weakest intermolecular bonds. London Dispersion Forces are present in every molecule and are caused by the random movements of electrons inside atoms. Sometimes a large of electrons congregates on one side of an atom, causing a temporary dipole. The more electrons in the molecule the stronger the LDF.
2. Dipole-Dipole Bonds
These exist only in polar molecules, where the negative and positive ends of molecules are attracted to the negative and positive ends of other molecules. These are stronger than London Dispersion Forces but weaker than Hydrogen Bonds.
A Polar Molecule
B. Hydrogen Bonds
When Hydrogen bonds with certain elements( Oxygen, Fluorine, Nitrogen, and in some cases Chlorine). Hydrogen Bonds are very strong and highly polar.
In the past lesson we learned how to determine whether a bond was polar or non-polar and whether it was covalent or ionic. The "polar" sub-types were found only in covalent bonds and the difference lay in how they shared their bonds.
In a polar bond, the electrons are shared unequally between two atoms.
The electrons are pulled closer to the more electronegative atom, giving that atom a slight negative charge and the other atom a slight positive charge.
In a non-polar bond, the electrons are shared equally between two atoms.
The electrons are not charged meaning the bond has no positive or negative end.
In the same way that we can differentiate between polar and non-polar bonds, we can classify molecules either as polar or non-polar.
A polar molecule has one end with a positive charge and another end with a negative charge
This means polar molecules have an overall charge separation
Polar molecules are also called dipoles (the prefix di- means two) because of its two charged ends
A non-polar molecule has neither positive or negatives charges on its ends
This means it is not a dipole
Determining Polarity
Being polar on non-polar gives a molecule a variety of different properties. If a molecule contains only non-polar bonds, it will be a non-polar molecule. However, a molecule that contains polar bonds is not necessarily a polar molecule.
To determine whether a molecule is polar, you need to look at more than just the polarity of its bonds. You need to look at the shape of the molecule.
*The shape of the molecule and the polarity of its bonds together determine whether the molecule is polar or non-polar*
But the shapes of molecules can get quite convoluted and require further learning on our part so to compensate for that we can look at the molecules symmetry. When observing the symmetry of the molecule to determine its polarity a good rule to keep in mind is this:
Polar molecules are unsymmetrical
And molecules can be unsymmetrical in two ways:
Different atoms
Different numbers of atoms
Non-polar molecules are symmetrical (usually)
The symmetry of a molecule is found by drawing the molecule's Lewis dot diagram or bond diagram and inspecting both the vertical and horizontal symmetries. Remember, symmetry is the quality of being made up of exactly similar parts facing each other or around an axis.
Examples:
Given the following compounds determine if it is a polar or non-polar molecule:
NH3
Lewis Diagram:
# of Lone Pairs Around Central Atom
1
# of Bonding Electron Groups Around Central Atom
3
Name of Shape
Pyramidal
Shape Diagram and Bond Dipoles
Symmetric?
Asymmetric
Polar?
Polar Molecule
C2H2
Lewis Diagram:
H : C ::: C : H
# of Lone Pairs Around Central Atom
0
# of Bonding Electron Groups Around Central Atom
2
Name of Shape
Linear
Shape Diagram and Bond Dipoles
Symmetric?
Symmetric
Polar?
Non-Polar Molecule
Below is a video that provides a more comprehensive explanation on this subject:
