Introduction to Organics Flashcards
What is organic chemistry?
The study of the structure, composition, properties, preparation and reactions of chemical compounds of carbon
What is catenation?
An elements ability to form bonds with atoms of the same element
What is the ability of an element to form bonds with atoms of the same element called?
Catenation
Describe the valency of carbon.
Tetravalency
Why does catenation occur so readily in carbon?
3
C is a relatively small atom
Forms covalent bonds
The C-C bond is strong
What is the molecular formula, what does it express?
It expresses the number and type of atoms in a molecule
What is the structural formula, what does it express?
It indicates how the atoms are arranged
How do you use the full Lewis dot structure?
2
Bonds are indicated by dots
Lone pairs are indicated by dots
Eg.
__..__
H:O:H
__..__
How do you use the Half Lewis dot structure?
2
Bonds are indicated by lines
Lone pairs are indicated by dots
What is a full displayed formula?
2
Half Lewis Structure
Bond angles are displayed
What is a skeletal formula?
4
Lines depict bonds
C and H atoms are not shown
End of each line segment is a C atom
Multiple lines represent multiple bonds
What does a pair of two parallel lines in a skeletal structure indicate?
It indicates a double bond
What does three sets of parallel lines in a skeletal structure indicate?
It indicates a triple bond
What are the benefits of 3D structures?
3
They include information on the bond angles
They show the shape of the molecule
They display the possibility of isomers and stereoisomers
In a 3D structure what is represented by a solid wedge?
Atoms above the plane of the page
In a 3D structure what is represented by a hashed wedge?
Atoms below the plane of the page
What are the disadvantages of 2D structures?
2
It takes time to draw correctly
It’s a poor representation of geometry
What determines the properties and reactions of a molecule?
The type of bond between atoms within the molecule
What does the type of bonds in a molecule depend on?
The location of electrons in that bond
Why do atoms form bonds?
Because the product formed is more stable than the isolated atoms
What are the two types of bonds?
Ionic bonding
Covalent bonding
What is ionic bonding?
Where positively and negatively charged ions (cations/anions) are held together by electrostatic forces of attraction (oppositely charged species attract)
What is covalent bonding?
This is where electron pairs are shared 50-50 between atoms
Why can bonds not be 100% ionic?
Because there is always some sharing of electrons between atoms e.g 80% ionic and 20% covalent
What is electronegativity?
How likely an electron is transferred from one element to another
What does an electronegativity difference of 0.0 indicate?
Pure covalent
What does an electronegativity difference between 0.1 and 0.5 indicate?
Non-polar covalent
What does an electronegativity difference between 0.5 and 1.9 indicate?
Polar covalent
What does an electronegativity difference of greater than 1.9 indicate?
Ionic
What is a dipole moment?
The arrangement and behaviour of electrons that gives atoms all of their physical properties
What does a molecules polarity depend on?
2
Molecular shape
The atoms electronegativity values
How do we know which atom in the covalent bond of a molecule is negative and which is positive?
The atom with the greater electronegativity is the negative and the smaller electronegativity is positive
Under what structural condition can a molecule be polar?
A molecule can only be polar if the structure of the molecule is not symmetric
What can a dipole moment be used to predict?
4
Compound solubility in the solvent
The mechanism of a chemical reaction
The optimum solvent for product separation by thin layer chromatography
The best solvent for the crystallisation of a solid
What is a solvent?
A liquid that serves as the medium for a chemical reaction and or acts as a reagent in a chemical reaction
What is a nucleophile?
Substance that donates a lone pair of electrons in a chemical reaction
Classify solvents.
Non polar
Polar
What is a non polar solvent?
A solvent with a small or zero dipole moment
What is a non polar solvent best at dissolving?
Non-polar reactants
Give an example of a non-polar reactant?
HCL
What is a polar solvent?
A solvent that has a large dipole moment
What is a polar solvent best at dissolving?
2
Polar compounds
Charged species such as ions
Classify polar solvents.
Polar protic
Polar aprotic
What is a polar protic solvent?
A solvent that has a O-H or N-H bond
Why are polar protic solvents important?
2
They can participate in hydrogen bonding - powerful intermolecular force
They serve as a source of protons (H+)
Why are polar aprotic solvents important?
They may have H atoms but they lack O-H or N-H bonds and therefore cannot H-bond with itself
Why are polar aprotic solvents important?
They don’t participate in reactions but serve only as a reaction medium
