SC7 - Types of Substance ✓ Flashcards
SC7a - What are polymers and monomers?
- Monomers are small simple molecules.
- When multiple of these join up in a chain, they form a polymer
SC7a - What is a compound?
Atoms of more than one element joined together by chemical (covalent) bonds
SC7a - Why aren’t simple molecular compounds able to conduct electricity?
- For something to be able to conduct electricity it must contain a charged particle that is free to to move.
- Their molecules aren’t charged and their electrons aren’t free to move
SC7a - Why do polymers have higher melting points than simple molecular substances?
- Polymer molecules tend to be long and so have more intermolecular forces than need to be broken, therefore require more energy. Also, the longer chains tend to get tangled up with one another.
- This is also why polymers are solid at room temperature whereas monomers are liquids and gases.
SC7a - Why do simple molecular compounds have low m.p/b.p?
- They are formed of covalent bonds
- While there are strong covalent bonds, the forces between molecules are weak meaning they require little energy to break
SC7b - What are allotropes?
Different structural forms of the same element
SC7b - Describe the structure and properties of diamond?
- Tetrahedral structure
- Four bonds per carbon atom
- Electrical insulator due to no free electrons
- High melting point due to strong covalent bonds
- Very strong due to tetrahedral structure
- Used for drills due to strength
- It is a giant molecular structure
SC7b - Describe the structure and properties of a fullerene?
- Fullerenes are spherical or tubular structures where each carbon atom is bonded to three others
- They are simple molecules
- They have low m.p/b.p due to weak intermolecular forces
- They are also soft and slippery
- Can conduct electricity due to delocalised electron
SC7b - Describe the structure and properties of graphite?
- High melting point due to strong covalent bonds
- Layers easily slide over eachother due to weak forces between them
- Three bonds per carbon atom
- Delocalised electron allows conduction of electricity
- Useful as a lubricant due to layers sliding
- Used for electrolysis as it is unreactive and cheap
- It is a giant molecular structure
SC7b - Describe what graphene is and it’s properties
- Fundamentally, graphene is just 1 layer of graphite.
- The sheet is just 1 atom thick, making it the lightest known material
- Covalent bonds make it extremely strong
- Free electron means it is an excellent conductor
SC7b - Where are diamond and graphite examples of?
Giant molecular structures: Huge 3D networks of atoms linked by bonds
SC7c - Describe metallic bonding
Release of Electrons: Metal atoms release some of their outermost (valence) electrons, which contribute to the sea of delocalized electrons.
Formation of Positive Ions: Once the electrons are released, the remaining parts of the atoms are positively charged ions, as they now have more protons than electrons.
Delocalized Electrons: The electrons that have been released can move freely throughout the structure, which allows metals to conduct electricity and heat.
Strong Electrostatic Forces: The attraction between the free-moving, delocalized electrons and the positive ions creates very strong electrostatic forces within the metal.
High Melting and Boiling Points: These strong forces of attraction result in high melting and boiling points for metals, as a lot of energy is required to break the bonds between the ions and the sea of electrons.
SC7c - How are metals malleable?
- Mallebale means that it can change shape and bend without breaking
- Metals are a giant lattice structure of positive metal ions delocalised electrons
- When a force is applied to a metal, the layers slide over each other
- It doesn’t break because of the ‘sea’ of delocalised electrons holding the metal together by electrostatic forces
SC7c - How does the electrical conductivity of a metal vary?
- Metals that form ions with higher charges contribute more electons to the ‘‘sea’’ of delocalised electrons, so there are more electrons avaliable to carry a current. Therefore, they have a higher electrical conductivity
SC7c - Why are metals able to conduct electricity?
- To be able to conduct electricity, something must contain a charged particle that is free to move
- Since metals have a sea of deloclised electrons, it meets these two requirements
- When a potenital difference is applied, the electrons move to the positive side
