Topic 2: bonding, structure, and properties of matter Flashcards
what is ionic bonding?
ionic bonding is the electrostatic attraction between positive and negative ions
it is a relatively strong connection
how are ionic compounds held together?
- held together in a giant lattice
- regular structure that extends in all directions in a substance
- electrostatic attraction between positive and negative ions hold the structure together
state the properties of ionic substances
- high melting and boiling point
- strong electrostatic forces between positively charged ions
- do not conduct electricity when solid (ions are in fixed proportions)
- conduct when molten or dissolved in water (ions are free to move)
how are ionic compounds formed, explain in terms of MgO
reaction of a metal with a non-metal
electron transfer occurs - metal gives away its outer shell electrons to non-metals
Mg is in group II, so has 2 available outer shell electrons
O is in group VI, so can accept 2 electrons to get a full outer shell configuration
Mg becomes Mg2+ and O becomes o2-
what is a covalent bond?
covalent bond is a shared pair of electrons between 2 atoms
describe the structure and properties of simple molecular covalent substances
- do not conduct electricity
- small molecules
- weak intermolecular forces, therefore
- low melting and boiling point
how do intermolecular forces change as the mass/size of the molecule increase
they increase
cause melting and boiling points to increase as well
what are polymers
polymers are very large molecules with atoms linked by covalent bonds
what are thermosoftening polymers
a special type of polymer
they melt/ soften when heated
there are no bonds between polymer chains
strong intermolecular forces ensure that the structure is solid at room temp
these forces are overcome by heating - polymer melts
List the properties of giant covalent substances?
- solids, atoms covalently bonded together in a giant lattice
- high melting and boiling points
- strong covalent bonds
- mostly don’t conduct electricity (no delocalized electron)
examples of giant covalent substances
diamond, graphite, silicon dioxide
describe and explain the properties of allotropes of carbon:
Diamond
- four very strong covalent bonds for each carbon atom
- very hard (explanation: strong bonds)
- very high melting point (explanation: strong bonds)
- does not conduct electricity (explanation: no delocalised electrons)
describe and explain the properties of allotropes of carbon:
fullerenes:
- hollow-shaped molecules
- based on hexagonal rings
explain the buckminsterfullerne structure
-c60 has a spherical shape, a simple molecular structure
describe and explain the properties of allotropes of carbon:
nanotubes
- cylindrical fullerene with a high length-to-diameter ratio
- high tensile strength (strong bonds)
- conductivity (delocalized electrons present)
describe and explain the properties of allotropes of carbon:
graphene
a single layer of graphite
describe and explain the properties of allotropes of carbon:
graphite
- 3 layers of covalent bonds for each carbon atom
- layers of hexagonal rings
- high melting point
- layers free to slide as weak intermolecular forces between layers: soft and can be used as a lubricant
- conduct thermal energy and electrical energy due to one delocalized electron per carbon atom
what is metallic bonding?
forces of attraction between delocalized electrons and nuclei of metal ions
describe the properties of metals
- high melting point and boiling point (explanation: strong forces of attraction)
- good conductors of heat and electricity (explanation: delocalized electron present)
- malleable, soft (explanation: layers of atoms can slide over each other whilst maintaining the attraction forces)
what are alloys
mixture of metal with other elements
why are alloys harder than pure metals?
different sizes of atoms distort the layers so they cannot slide over each other therefore alloys are harder than pure metals
what is the melting and boiling point of simple covalent bonds?
loe due to weak intermolecular forces between molecules
what is the conductivity when a solid of simple covalent bonds
poor, no ions to conduct
what is the conductivity when molten of simple covalent bonds?
poor due to no ions to conduct
what is the general description of simple covalent bonds?
mostly gases and liquids
what is the boiling point and melting? point of ionic bonds
high due to a giant lattice of ions with strong forces between oppositely charged ions
what are the melting and boiling points of giant covalent bonds?
high because of many strong covalent bonds between atoms in giant structure
what is the conductivity when a solid of ionic bonding
poor due to ions not being able to move
what is the conductivity when molten ionic compounds?
good due to ions are free to move
what is the general description of ionic bonds?
crystalline solid
what is the conductivity when a solid of giant covalent bonds
Diamond and sand: poor, because electrons cannot move
graphite: good as they have delocalized electrons between layers can move through the structure
what is the conductivity when molten of giant covalent bonds
poor
general description of giant covalent bonds
solids