structure and bonding Flashcards
what is an ion?
an atom or group of atoms that has lost or gained electrons and therefore has a positive or negative charge.
what is a covalent bond?
a bond involving shared pairs of electrons between atoms- molecules are held together by covalent bonds
what is metallic bonding?
when positively charged metal ions are surrounded by delocalised outer electrons
what are electrostatic forces of attraction?
strong forces of attraction between oppositely charged particles eg Na+ and Cl-
what bonds do metals and non-metals form?
ionic
what elements form covalent bonds?
non-metals
what elements form metallic bonds?
metals and alloys
what are examples of giant covalent structures?
diamond, graphite, silicon dioxide
what is a monomer?
a small compound whose molecules can join together to form polymers
what is a polymer?
a long molecule consisting of many similar or identical monomers linked together.
what is a limitation of dot and cross diagrams?
they do not show the 3D shape of a molecule
how are group numbers and charges linked?
the group of an element tells us the charge on that atom- eg barium is in group 2 so it has a charge of 2+, iodine is in group 7 so it has a change of -1
what is a giant atomic lattice?
a huge, 3D, regular structure of oppositely charged ions, held together by electrostatic forces.
what is a delocalised electron?
an electron that is able to move freely throughout a structure- enables charge to be carried through
how do ions become positive?
by losing outer shell electrons- number of protons in nucleus > number of electrons in shells
how are metals bonded?
they are in a lattice shape- positive ions surrounded by a sea od delocalised electrons
why are metals malleable?
the layers of metal ions can slide over each other
why are alloys harder than pure metal?
the differently sized atoms disrupt the layers of ions and prevent the layers from sliding
how can ionic compounds not carry charge when solid but can when molten/in solution?
when they are molten the ions are free to move and carry charge whereas they are fixed in their solid state
why do ionic substances have high boiling/melting points?
strong electrostatic forces between opposite ions need lots of energy to break
what is an allotrope?
different forms/shapes of the same element eg diamond and graphite are carbon allotropes.
why is diamond so hard?
each of the carbon atoms form 4 other covalent bonds in a tetrahedral structure, so it is very hard to break.
how many bonds are in graphite?
each carbon bonds forms 3 other bonds, leaving one electron delocalised and free to carry charge
why is graphite so soft?
there are strong bonds between atoms but weak IMF between layers of atoms, which means that they can slide over each other.
what is graphene?
a single layer of graphite that is one atom thick. it is used in electronics and composites
what is a composite?
materials made of two or more different materials, containing a matrix and a reinforcement- often used to combine desirable properties of each
what is buckminsterfullerene?
carbon c60- 60 carbon atoms arranged as a hollow sphere. useful for drug administration
what are carbon nanotubes?
tiny, hollow tubes made of carbon atoms with a high length to diameter ratio
what are some properties of carbon nanotubes?
high tensile strength, high electrical + thermal conductivity. used in electronics and strong materials
what are nanoparticles?
very very small particles- usually between 1 and 100 nanometres in size and contain only a few hundred atoms
