P1 1g covalent bonding Flashcards
what is a covalent bond?
two or more atoms sharing electrons
how is a covalent bond formed?
when two atoms can share electrons so both can have a full outer shell
how do you use dot and cross diagrams for covalent bonds?
dot for one element cross for the other, drawn like a Venn diagram, bit in the middle shows shared electrons
what are the substances covalent bonds make?
- simple molecular substances
- polymers
- giant covalent structures
what are the intermolecular forces like between the molecules?
weak intermolecular forces, only between each individual molecule
are the covalent bonds strong?
yes very
what are polymers?
long chains of monomers
what are giant covalent structures?
arranged in a regular lattice, hydrogen bonds
what is the electrostatic attraction like in covalent bonds?
strong electrostatic attraction between the shared pair of electrons and the nuclei of the atoms involved (electrons are negative and nuclei is positive)
do simple covalent bonds conduct, why?
no, because they do not contain free moving electrons
why do simple molecular structures have low melting and boiling points
weak intermolecular forces acting between neighbouring molecules
why are most small molecules gases or liquids at room temp?
forces are very weak
why does the melting and boiling point increase?
because the relative molecular mass of a substance increases, and more energy is required to break the bonds and there are more intermolecular forces between them
what happens when a covalent molecule boils?
the intermolecular forces are broken but not the covalent bonds, hence water not turning into hydrogen and oxygen
what is a giant covalent structure like?
- very strong covalent bonds
- high melting and boiling points
- don’t conduct electricity
why does a giant covalent structure have high melting and boiling points and are stronger?
because they are covalently bonded all around, and are in a regular repeating lattice
what are the properties of diamond?
- regular 3D lattice of covalently bonded atoms
- each carbon atom is covalently bonded to 4 other carbon atoms
- high melting point
- strong
- doesn’t conduct
- very hard
what is silicon dioxide made up off?
silicon, and oxygen.
what is an allotrope?
different structural forms of the same element in the same physical state
what are the properties of graphite?
- each carbon atom is bonded to only three others
- hexagon shapes, flat sheets, arranged on top of many layers
- no covalent bonds in-between layers (weak)
- soft
- high melting points bc of covalent bonds
- extra electron is delocalised which means it conducts electricity and heat
what is graphene?
a single flat sheet of graphite, a layer
what is fullerene?
spheres or tubes made up of graphene
- scientifically made
properties of graphene?
- conducts bc is has a delocalised pool of electrons
- strong
properties of fullerene?
- large surface area : volume ratio means its a good catalyst
- tubes can conduct electricity
what is fullerene used for?
- industrial catalysts
- nanotubes in nanotech
- used to strengthen materials
what is graphene used for?
electrical uses and can be made into fullerenes
what is buckminsterfullerene?
hollow sphere, with 60 carbon atoms
C60
