C2: Bonding, structure and the properties of matter Flashcards
define ionic bonding
- bonding involving the electrostatic attraction between positive and negative ions
- it is a relatively strong attraction
give two ways ionic compounds are held together
- held together in a giant lattice
- electrostatic attraction between positive and negative ions
state 3 properties of ionic substances
- high melting and boiling point ( strong electrostatic forces between oppositely charged ions)
- do not conduct electricity when solid ( ions in fixed positions)
- do conduct when molten or dissolved in water- ions are free to move
how are ionic compounds formed? Explain in terms of MgO case
- reaction of a metal with a non-metal
- electron transfer occurs ; metal gives away its outer shell electrons to non-metal
- Mg is in group 2 so has 2 outer shell electrons
- O is in group 6 so accepts 2 electrons to get a full outer shell configuration
what is a covalent bond?
- a shared pair of electrons between two atoms
Describe the structure and properties of simple molecular covalent substances (4)
- do not conduct electricity ( no ions)
- small molecules
- weak intermolecular forces thus:
- low melting and boiling points
how do intermolecular forces change as the mass/size of the molecules increases?
- they increase
- that causes melting/boiling points to increase as more energy is needed to overcome these forces
define polymer
- polymers are very large molecules with atoms linked by covalent bonds
- made up of repeating subunits known as monomers
what are thermosoftening polymers?
- special type of polymers that melt/soften when heated.
give three properties of thermosoftening polymers
- there are no bonds between polymer chains.
- strong intermolecular forces ensure that the structure is solid at room temperature
- these forces are overcome with heating - polymer melts
what are giant covalent substances?
- give two characteristics
- give 3 examples
- solids where atoms are covalently bonded together in a giant lattice
- high melting/boiling points - strong covalent bonds
- mostly don’t conduct electricity ( no delocalised e-)
- eg, diamond, graphite, silicon dioxide
define an allotrope and give the 5 allotropes of carbon
- different structural forms of an element
- diamond, graphite, fullerenes, nanotubes, graphene
describe the structure of diamond
- four, strong covalent bonds for each carbon atom
give 3 properties of diamond
- very hard (strong bonds)
- very high melting point ( strong bonds0
- does not conduct ( no delocalised electrons)
describe the structure of graphite
- three covalent bonds for each carbon atom
- layers of hexagonal rings
Give 4 properties of graphite
- high melting point due to strong covalent bonds
- layers free to slide as weak intermolecular forces between layers
- soft and so can be used as a lubricant
- conduct thermal and electricity due to one delocalised electron per each carbon atom
describe the structure of a fullerene and give an example
- hollow shaped molecules
- based on hexagonal rings but may have 5-7 carbon rings
- C60 has spherical shape, simple molecular structure called ‘ Buckminsterfullerene’
Give three properties of a fullerene
- high tensile strength
- high electrical and heat conductivity
- high ductility
describe the structure of nanotubes
- cylindrical fullerene with high length to diameter ratio
give two properties of nanotubes
- high tensile strength ( strong bonds)
- conductivity ( delocalised electrons)
what is graphene?
- a single layer of graphite
what is metallic bonding?
- forces of attraction between delocalised electrons and nuclei of metal ions
give three properties of metallic structures
- high melting /boiling points ( strong forces of attraction)
- good conductor of heat and electricity (delocalised) electrons
- malleable, soft ( layers of atoms can slide each other whilst maintaining the attraction forces)
why are they harder then pure metals ?
- different sizes of atoms distorts the layers
- so they can’t slide over each other
- alloys are harder than pure metals
what are alloys?
- mixtures of metal with other elements, usually metals
describe a simple covalent structure:
- low boiling and melting points due to weak intermolecular forces between molecules
- poor conductivity when solid as no ions to conduct
- poor when molten no ions
- mostly seen in gases and liquids
describe a ionic structure : include
- boiling and melting points
- conductivity when solid and when molten
- general description
- high because of giant lattice of ions with strong forces between oppositely charged ions
- poor : ions can’t move
- good: ions are free to move
- crystalline solids
describe a giant covalent structure: include
- boiling and melting points
- conductivity when solid and when molten
- general description
- high because of many strong covalent bonds between atoms in giant structure
- diamond and sand: poor because electrons can’t move; graphite : good as free delocalised electrons between layers can move through structure
- conductivity when molten: poor
general description: solids
describe a metallic structure: include
- boiling and melting points
- conductivity when solid and when molten
- general description
(CAN BE USED FOR A GENERAL METAL EG MAGNESIUM)
- high - strong electrostatic forces between positive ions and delocalised electrons
- good: delocalised electrons are free to move through structure
- good
- shiny metal solids
give two limitations of three dimnesional and two dimensinal models
2D
- do not give accurate information on the shape of molecule
- only shows one layer
give 2 benefit and two limitations of a ball and stick diagram
- can see ions in 3 dimensions
cons: - unable to tell which electron in the bond came from which atom
- do not show outer electrons in the bond
give two limitations of the dot and cross diagrams
- do not tell us the shape of the molecule
- how the ions are arranged in space
what are limitations of the simple model?
- there are no forces illustrated between spheres and atoms, molecules and ions re solid spheres- this is not true
what does the amount of energy needed to change state from solid to liquid or liquid to gas depend on
- the strength of the forces between the particles of the substance
- the nature of the particles involved depends on the type of bonding and structure of the substance
- the stronger the forces between the particles the higher the melting point and boiling point of the substances
when will a pure substance melt or boil at?
- a fixed temperature
- a mixture will melt over a range of temperatures
give the three states of matter
solid
liquid
gas
what is nanoscience?
- science that studies particles that are 1-100nm in size
state 5 uses of nanoparticles
- medicine ( drug delivery systems)
- electronics
- deodorants
- sun creams ( better kin coverage and more effective protection against cell damage)
- catalysts
what are fine and coarse particles?
- give the diameter range
fine particles ( soot) ; 1 x 10-7 m and 2.5 x 10-6 m diameter
coarse particles ( dust); 1 x 10- 5 m and 2.5 x 10- 6 m
why do nanoparticles have properties different from those for the same materials in bulk
- high surface area to volume ratio
What shape are
nanoparticles
approximated to?
a cube
What happens to the
surface area to volume
ratio of a cube if you
decrease the side of a
cube by a factor of 10?
The SA:V ratio increases by a factor of 10
. Why are
nanoparticles used
instead of the same
material in bulk?
less needed for the same effect
give 5 uses for fullerenes
- drug delivery (round the body)
- hydrogen storage
- anti-oxidants
- reduction of bacterial growth
- catalysts
