Organic Chemistry Review

Question 1

State the 3 allotropes of carbon, defining what allotopes are. State the type of carbon that is molecular.

Answer 1

3 Allotropes:
1) Diamond
2) Graphite (graphene)
3) Fullerene

Allotropes of the same element can vary in both physical and chemical properties.

The bonds are held together in giant 3-D lattice structures (in large networks or chains)

Question 2

State VSEPR shape, angle, electrical conductivity, and features of the 3 carbon allotropes.

Answer 2

Pure Carbon:
- Tetrahedral (109.5 degree angle)
- MP of 4000 degrees celsius
- Electrical conductivity: No, as the electrons cannot move freely

Graphite:
- Trigonal-planar (120 degree angle)
- Electrical conductivity: Yes
- 2 uses: pencils, lubricants

Graphene:
- Trigonal planar (120 degree angle)
- Electrical conductivity: Yes, better because 2D
- Features of graphene: Strong, flexible, LCDs, lubricants

Fullerene:
- Fullerene is formed when vaporized carbon condensed in an atmosphere of inert gas
- The shape is an icosahedral cage, a soccer ball.
- Trigonal planar (120 degree angle)
- Electrical conductivity: No, weak london forces

C60 Fullerene is not a covalent network solid, so is different from the other allotropes of carbon. The C60 molecules have strong covalent bonds but weak London forces between molecules.
State two uses of C60 Fullerene: medical monotubing.

Question 3

Provide examples of giant covalent macromolecule structures

Answer 3

• Carbon, Silicon, and Silicon Dioxide. All are giant molecules with high MP’s and BP’s.

Question 4

Compare and contrast CO2 and SiO2

Answer 4

CO2:
Gas, non-polar, very low boiling point, linear 180 degrees

SiO2:
- Commonly known as quarts,
- often represented as SiO2/4,
- in a solid state silicon is bonded to 4 other silicon atoms or oxygen atoms
- very high Mp’s and BP’s - 1600 degrees Celsius
- Silicon and silicon dioxide have giant tetrahedral structures

Question 5

Draw a Lewis structure model representing methane, ammonia, and water

Answer 5

bro just check idk

Question 6

Describe the difference between single/double bond’s lengths and strengths

Answer 6

SINGLE BONDS: longest, weakest

DOUBLE BONDS: longer, stronger

TRIPLE BONDS: shortest, strongest

Length is measured in picometers, energy is mmeasured in kj/mol – the amount of energy that must be ABSORBED to break the bond

Question 7

Recall the strength required to break single bonded carbons, double bonded carbons, and triple bonded carbons AND the length of the bond

Answer 7

TRICK QUESTION!!! it’s on the data booklet on pages 10 and 11, don’t even try to memorise its a waste of time

Question 8

Recall the physical and chemical properties of a homologous series

Answer 8

PHYSICAL: melting and boiling points will INCREASE as we add CH2

CHEMICAL: chemical properties are the same for the homologues series

Question 9

Draw out Si O2

Answer 9

bro just check u must be able to do this he literally said it’s on the test

Question 10

Outline delocalisation.

Answer 10

DELOCALISATION occurs when the is resonance – it can exist in more than one position.

Electrons can exist in any place at any time

Question 11

Outline the difference between molecular polarity and bond polarity, using water and methane as examples

Answer 11

1. MOLECULE POLARITY: use vector addition and have a net pole in one direction
2. BOND POLARITY: unequal sharing of electrons

Examples:

1. water is a polar molecule, with oxygen having a partial negative and hydrogen having a partial positive charge.
2. Methane’s C-H bonds are slightly polar, but the molecule is symmetrical so the bond dipole cancel out – the molecule is non-polar

Question 12

Outline VSEPR theory

Answer 12

VESPR: valence shell electron pair repulsion theory

For the shape created, there is a distinguishment between:

1. Electron domain geometry: based on the electron domains (area of electron density) for any atom, especially around the central atom
2. Molecular geometry: this is the shape of the entire molecule (or part of it)

Double and triple bonds act as a SINGLE DOMAIN.

Question 13

Outline the working method to produce structures

Answer 13

1. Decide on the central atom
2. Decide how many bonds for each atom are involved (bonding pairs and lone pairs)
3. Each bond will involve one electron from each of the atoms it joins (unless it’s a dative/coordinate bond)
4. Produce a dot/cross lewis structure, replace each bond and line for an electron pair
5. If the species is an ion rather than the molecule, than one electron needs to be added for each negative charge (and one removed for each positive charge)

Question 14

Define a coordinate or dative bond

Answer 14

A coordinate bond is a type of bond in which the bonding electrons are shared between two atoms at the corners of a tetrahedral molecule.

It is called a coordinate bond because the atoms act like “coordinates” or locations where the bonding electrons are located.

Coordinate bonds can also be represented as a straight line between the two atoms in a molecule.

They typically involve metals with a high degree of electronegativity, such as chlorine or oxygen.

Question 15

Outline the 6 molecular shapes, number of bonding pairs, lone pairs, and bond angles, with examples.

Answer 15

LINEAR:
BP:
LP:
Angle:

TRIGONAL PLANAR
Example:
BP:
LP:
Angle:
Example: