C2: Bonding, structure and properties of matter Flashcards
What is covalent bonding?
Atoms share pairs of electrons to become more stable.
What type of elements bond covalently?
Non-metals.
Are covalent bonds strong or weak? Why?
Strong; the positive nuclei are attracted to the shared pairs of electrons (electrostatic forces).
Give 7 examples of simple covalent substances (name and symbol).
Hydrogen - H2 Methane - CH4 Nitrogen - N2 Hydrogen chloride - HCl Oxygen - O2 Chlorine - Cl2 Water - H2 O
Describe the bond(s) in oxygen. What is this type of compound called?
Double covalent bond.
Diatomic, and simple molecular/covalent structure.
Describe the bond(s) in Hydrogen. What is this type of compound called?
Single covalent bond.
Diatomic, and simple molecular/covalent structure.
What are the bonds between atoms called?
Intramolecular.
What are the bonds between molecules called?
Intermolecular.
List and explain the properties of simple covalent substances.
~Low melting and boiling points: gases/liquids at room temperature - molecules easily parted (weak intermolecular forces).
~The more there is of the substance, the stronger - cumulative intermolecular forces increase; more energy needed to break bonds.
~Never conduct electricity - no charge or free ions/electrons.
What is a polymer?
A long chain of repeating units: monomers.
Lots of monomers are linked (bonded covalently and strongly) to form a long molecule with repeating sections- the polymer.
How can a polymer be realistically drawn? Draw poly(ethene).
( H H ) Shown in the brackets is the monomer.
( | | ) The lines through the brackets show where it
-(–C–C–)- joins to the next unit.
( | | )
( H H )n
How are molecular formulae of polymers written?
Formula of monomer in brackets.
“n” or a given number outside the right bracket, in subscript.
E.g. (C2 H4)n
How do the forces in polymers compare to those in other types of substance?
Larger than simple covalent molecules. More cumulative intramolecular force so more energy needed to break them. Usually solids at room temperature.
These forces are still weaker than ionic or giant covalent compounds so they generally have lower melting/boiling points.
What is another term for giant covalent structures?
How are these formed?
Macromolecules.
All the atoms are linked by strong covalent bonds.
What are the properties of macromolecules and why?
Very high melting/boiling points - lots of energy needed to break the intramolecular forces.
Don’t conduct electricity, except graphite - no ions/electrons able to more and no charge.
Give the 3 main macromolecules.
Diamond, graphite and silicon dioxide/silica/sand.
What is the term used to describe each of at least 2 different physical forms in which an element can exist?
Give an example.
An allotrope.
E.g. allotropes of carbon are diamond, graphite and graphene.
Describe the structure and properties of diamond.
Diamond is a rigid, giant covalent lattice made of carbon. Each carbon atoms forms 4 covalent bonds, making it a rigid tetrahedral structure whose strong covalent bonds require large amounts of energy to overcome, giving it a high melting/boiling point.
Diamond does not conduct electricity because it has no mobile electrons or ions to carry current.
Describe the structure and properties of graphite.
Each carbon atom forms 3 covalent bonds, creating sheets of hexagons. 3 out of 4 of graphite’s outer electrons are bonded, leaving one delocalised electron per atom. It can conduct electricity and heat because of this.
No covalent bonds between layers; they are held together weakly and can slide over each other. It is therefore soft and slippery.
High melting/boiling point - strong covalent bonds need lots of energy to be broken.
Describe the structure and properties of graphene.
One layer of hexagonally arranged carbon atoms. Only one atom thick; it is a 2D compound.
Covalent bonds make it strong, though it is light, so can be added to other materials to add strength but not much weight.
3 out of 4 outer electrons are bonded, leaving one delocalised electron per atom. It can conduct electricity and heat because of this.
What are fullerenes?
Molecules of carbon shaped like closed tubes or hollow balls. Can be made of carbon heptagons or pentagons- but usually hexagons.
What are the 2 types of fullerene?
Nanotubes - tiny cylinders.
Bucky balls - hollow balls.
Describe the structure and uses of fullerenes.
They can cage molecules so could deliver a drug into a specific location in the body.
Large surface area so catalyst molecules could be attached to them for industrial purposes.
They can make good lubricants.
Nanotubes have a high ratio of length to diameter so they do not break when stretched. They can also conduct heat and electricity.
What is the name for technology that uses very small particles, such as fullerenes? Why are they useful?
Nanotechnology.
They can add strength but minimal weight, amongst other uses.
