C2 (bonding, structure, the properties of matter) Flashcards
how does ionic bonding work? use lithium, a metal, and fluorine, a non-metal, in your example:
- neither lithium or fluorine have a full outer energy level; lithium has 1 electron in its outer energy level, fluorine has 7.
- lithium can react to lose one electron to gain a full outer energy level, and fluorine can use this electron to fill its outer energy level. now both fluorine and lithium are stable ions.
- lithium lost an electron, and so has a charge of 1+, and fluorine gained an electron, and so has a charge of 1-.
between which elements does ionic bonding occur?
ionic bonding occurs between metal and non-metals. this means they are oppositely charged ions. in the end, both atoms have the structure of a noble gas.
how does covalent bonding occur? use two hydrogen atoms in your example:
- hydrogen atoms have only one electron in their outer shells, and they require two.
- the two hydrogen atoms overlap their electron shells, and now both atoms have two electrons in their outer electron shells.
- these two hydrogen atoms are now stable
- covalent bonding only occurs between two non-metal atoms
what are the formulae for ammonia and methane?
- ammonia = NH3
- methane = CH4
describe metallic bonding:
- occurs when metals bond with other metals
- metals are giant structures of atoms, arranged in a regular pattern. when these atoms are together, they give up their electrons in their outer shells, and share them with all the other atoms DELOCALISED ELECTRONS
- these atoms all become positive ions
- there is now a strong electrostatic attraction between the positive ions and the negative electrons, and this holds everything together in a regular structure
- ‘sea of electrons surrounding a positively charged lattice’
what is an ionic compound?
giant structure of ions. held together by strong electrostatic forces of attraction between oppositely charged ions. these forces act in all directions in the lattice, and this is called ionic bonding.
what are the limitations of using different diagrams to represent ionic compounds?
- dot and cross:
a: dots to represent one atom’s electrons, crosses to represent the other. very clearly shows where the electrons are coming from.
d: don’t tell us about the shape of the molecule, or the 3D arrangement of electrons. - 2D stick diagram:
d: can’t tell which electron in the covalent bond came from which atom. give us no idea of outer electrons that aren’t in bonds. do not accurate info on the shape of the molecule. - 3D stick diagram:
a: shows shape of the molecule. - ball and stick diagram:
a: we can clearly see the ions in 3D.
d: the ions are shown as widely spaced, when in reality, they’re packed together. gives impression that structure is small. - space filling diagramL
a: gives better idea of how closely packed the ions are.
d: can be difficult to see the 3D packing. gives impression that the structure is quite small.
what characteristics does an ionic lattice give metals?
this means that metals are incredibly strong, have high melting and boiling points, and are good conductors of electricity and heat (delocalised electrons can carry heat and electricity through the metal).
- also malleable (as they’re such a regular structure, the different layers can slide over one another) - the case for PURE METALS, as all the electrons are regular shapes
why are alloys so strong?
- alloys contain two or more different elements, with different sized atoms (e.g. steel)
- these different sized atoms disrupt the metal’s regular structure, and means that the atoms can no longer easily slide over one another, making the alloy much harder than pure metal
what are the properties of metals and alloys?
- metals have giant structures of atoms with strong metallic bonding. therefore most metals have high melting and boiling points.
- in pure metals, atoms are arranged in layers, making the metal easily bent and shaped.
- good conductors of electricity as the delocalised electrons in the metal carry electrical charge through it. this goes the same for thermal energy.
what do ionic compounds form?
- they form giant ionic lattices. every positive ion is surrounded by a negative ion, and vice versa.
- giant ionic lattices are 3d, and have very strong forces of attraction between the ions (ELECTROSTATIC FORCES = ionic bonds)
what are the properties of ionic compounds?
- very high melting and boiling points (strong electrostatic forces require a lot of heat energy to break)
- they cannot conduct electricity when they’re solids, as the ions cannot move (the electrostatic forces lock them in place)
- WHEN IONIC COMPOUNDS CONDUCT ELECTRICITY, IT’S THE IONS THAT MOVE, NOT THE ELECTRONS!
what are the properties of small covalent molecules?
- low melting and boiling points (usually gases/liquids at room temperature)
> the intermolecular forces are
incredibly weak, and don’t require very
much energy to break - it’s these that
are overcome, not the covalent bonds - don’t conduct electricity (because they’re neutral, and don’t have any charged particles to move and carry the charge)
- the intermolecular forces increase with the size of the molecule, so larger molecules have higher melting and boiling points as they have more intermolecular forces, which require more energy to overcome.
what is a polymer, and what are their properties?
- each giant polymer molecule is made up of smaller molecules, called monomers.
- a single polymer is strong, as its connecting covalent bonds are strong. however, to break up multiple polymers, you’d have to break the intermolecular forces, which are much weaker.
- however, polymers are long and have a large surface area, and so the accumulated intermolecular forces are quite difficult to break.
- lower melting and boiling points than giant structures, but higher points than simple structures (e.g. water)
- generally solid at room temperature
what is a property of giant covalent molecules?
- always solids at room temperature (many strong covalent bonds - high melting and boiling points)
