C2

Covalent bonds and carbon

Covalent bonds

What are they: A chemical bond made when to or more atoms share one or more electron pairs

Why are diamonds hard/ high boiling point

  • Each carbon atom connects to 4 other carbon atoms

  • This means every atom shares all 4 valance electrons

  • This means each atom forms a covalent bond with other atoms

  • This forms a uniform giant covalent structure

  • And because covalent bonds are very strong and require lots of energy to break

  • The entire structure of the diamond is strong and hard to break

Why are diamonds not very good conductors

  • Each carbon atom connects to 4 other carbon atoms

  • This means every atom shares all 4 valance electrons

  • This means each atom forms a covalent bond with other atoms

  • This means that there are no delocalised electrons that are free to move across the structure and carry charge or thermal energy

  • As all the electrons are already bonded to another carbon atom

Metallic bonding

Now 6 mark questions are usually graded in bands meaning that on top of having to know your stuff you have to put in the words they like, always be very meticulous with explaining because and why using every piece of terminology you can think of, create an answer that is impossible to misinterpret .

Metallic bonds

What is a metallic bond?

  • By definition it is the electrostatic attraction between positive metal ions and delocalised electrons

Why metals are malleable?

  • metals form positive metal ions bonded together With a sea if delocalised electrons around them

  • As you move across the periodic table the number of delocalised elections increase e.g. Mg,+2 Fe+3

  • These metal ions and electrons are held in place by strong electrostatic forces between the negative electrons and positive metal ions

  • This creates a giant regular structure, arranged in layers

  • This may lead to the metal being malleable as the layer slide over each other, however because of the strong electrostatic forces between the sea of negative electrons and the positive metal ions, The metal does not break

Why alloys are hard?

  • In a pure metallic structure, positive metal ions are held in place by strong forces of electrostatic attraction in a regular structure

  • This means that metal ions are arranged in pattern with multiple layers

  • Which works because all of the atoms are made up of the same element and thus the same size

  • When different elements are added, they don’t fit in with this regular structure as they have are a different size to the other metal ions

  • This causes the layers of the giant metallic structure to distort

  • This makes it harder for the layers too slide over each other, making the alloy less malleable and more hard.

    Conductors

There will commonly also be questions asking why a metal or nanoparticle or graphite is a good conductor of electricity, The good thing about this is that commonly the answer is the same, it just is in the context of the structure in question: e.g.

Why can metals conduct electricity/ heat?

  • This is because in a metallic structure positive ions are bonded together in a giant metallic structure held in place by a sea of negative electrons

  • These negative electrons however are delocalised as they are not bonded to any particular metal ion

  • Meaning that they are free to move across the structure of the metal, and carry charge / thermal energy.

It'll always come down to -delocalised electrons, Carry charge and move through the structure, the rest of the marks in the question will come down to context and clarity