Covalent molecules and Allotropes of Carbon Flashcards
(20 cards)
What substances usually consist of small covalent molecules and why?
Gases or Liquids due to the weak intermolecular forces between small covalent molecules- so they can easily exist in these states as only a small amount of energy is required to transition between these states
Do substances containing small covalent molecules have high or low boiling points and why?
Small covalent molecules have low melting/ boiling points due to their WEAK intermolecular forces between molecules.
What is overcome when the substance consisting of small covalent molecule boils/melts?
The Weak Intermolecular forces are overcome when the substance boils or melts.
What is the exception of small covalent molecules?
Water is a special case as it has Hydrogen bonding which makes it’s intermolecular forces stronger than other simple covalent molecules.
What is definitely not overcome in Small Covalent molecules?
The Intramolecular covalent bonds are STRONG, and remains intact as the forces of the molecules are being broken, not the molecule itself.
What is different from longer covalent molecules and simple covalent molecules, regarding boiling and melting points?
The intermolecular forces increase with the size of the molecules. Longer molecules have higher melting/boiling points as they have a higher surface area but these are still relatively low compared to ionic compounds.
Name a use of Longer covalent molecules and why?
Oils have large covalent molecules so we use various oils to cook in due to their reasonable boiling points.
What are Polymers?
Name their properties
Polymers are very large/long covalent molecules
-The atoms in Polymers are linked to other atoms by STRONG covalent bonds
-The intermolecular forces between Polymer molecules are relatively strong so require alot of energy to be overcome so
-They have high melting/boiling points
-Polymers are Solid at room temperature
Why don’t Covalent molecules conduct electricity?
Covalent molecules don’t conduct electricity because they do not have electrons that are free to move to carry a charge
Also, the molecules don’t have an overall electric charge as there is no ions
Why are people scared of dropping electrical equipment in water?
When water is pure or distilled, it is an electrical insulator, meaning it doesn’t conduct electricity. However, impurities, such as sweat + salts which contains ions, means water is able to conduct electricity.
List the properties of Silica
Silica is a Giant Covalent Structure
-VERY high melting point as all of the atoms in a giant covalent structure are linked to other atoms by strong covalent bonds so require a lot of energy to be overcome.
-In Silica, these BONDS must be overcome to melt or boil these substances
Describe all of Diamond’s properties and it’s structure.
Diamond is made of carbon atoms. Each carbon atom is bonded to FOUR other carbon atoms.
-This Gives Diamond a tetrahedral structure (carbon atoms give it a tetrahedral network) - it is a Giant Covalent structure
-Is very HARD + STRONG because of the strong Covalent bonds
- High mp/bp cs of the # of Covalent bonds between Carbon atoms so large amount of energy to overcome
-cannot conduct electricity or heat
Describe the structure and properties of Graphite!
In Graphite, each carbon atom form covalent bonds with three other carbon atoms (rather than 4) - this means that one electron is delocalised per Carbon atom.
This free electron is able to move through the structure, conducting charge + energy.
-This forms layers/ sheets of hexagonal rings.
-The layers are held together by weak intermolecular forces so they can SLIDE over eachother- this make Graphite BRITTLE.
-Cs of this, Graphite is also SOFT + SLIPPERY so is a good lubricating material
-Can conduct electricity
-High mp due to it’s giant covalent structure but the weak intermoleculer forces between layers means it requires less energy to melt/boil than diamond
What do you overcome when melting Graphite?
When melting Graphite, you overcome the weak INTERMOLECULAR FORCES between the LAYERS.
Why is Graphite softer than diamond?
Each carbon atom in graphite forms three covalent bonds with other carbon atoms, creating hexagonal rings that are arranged in layers. These layers are held together by relatively weak forces. These weak forces allow the layers to slide over each other, making graphite soft and slippery, while, in Diamond, each carbon atom is bonded to four others in a rigid, three-dimensional network held together by strong covalent bonds
Describe Graphene
Graphene is a single, hexagonal layer of Graphite.
-Is 2D, as Carbon atoms are joined together in hexagons
-High mp as lots of energy needed to overcome the strong covalent bonds
-Has useful properties in Electronics and Composites
- A very strong but lightweight material
Describe Fullerenes
Fullerenes are molecules with Carbon atoms with hollow shapes.
-It’s structure is based on hexagonal rings of carbons but may also contains rings with 5 or 7 carbon atoms so can be heptagons or Pentagons
The first fullerene to be discovered was Buckminsterfullerene (C60), which has a spherical shape.
What is an allotrope?
Allotropes are different structural forms of the same element (jn this case, Carbon), in the same physical state.
Name the Solid carbon allotropes
-Diamond
-Graphite
-Fullerenes
-Nanotube
