Module 3: Section 1 Flashcards
(97 cards)
What is a giant covalent lattice?
a huge network of covalently bonded atoms.
What is another name for a giant covalent lattice?
macromolecular structure.
What is an allotrope?
a different form of the same element in the same state.
Name the 3 allotropes of carbon.
diamond, graphite, graphene.
In diamond, how many covalent bonds does each carbon atom form?
each carbon atom is covalently bonded to 4 other carbon atoms.
In diamond, what shape are the atoms arranged in?
tetrahedral shape. (crystal lattice structure)
What does ‘sublimes’ mean?
when a substance changes straight from a solid to a gas, skipping out the liquid stage.
What properties are caused by lots of strong covalent bonds in diamond?
- very high melting point (it sublimes at over 3800K)
- extremely hard (used in diamond-tipped drills and saws)
- good thermal conductor (vibrations travel easily through the stiff lattice)
- insoluble in any solvent
- can’t conduct electricity (no delocalised electrons)
Why are diamonds ‘cut’ to form gemstones?
it’s structure makes it refract light a lot, so it sparkles.
In silicon, how many covalent bonds does each atom form?
each silicon atom forms 4 strong covalent bonds
What structure does silicon form?
silicon (same periodic group as carbon) forms a crystal lattice structure with similar properties to carbon.
In graphite, how many covalent bonds does each carbon atom form?
each carbon atom is covalently bonded to 3 other carbon atoms.
What is the structure of graphite?
- carbon atoms are arranged in sheets of flat hexagons covalently bonded with 3 bonds each
- the fourth outer electron of each carbon atom is delocalised between the sheets of hexagons
- the sheets are bonded together by weak induced dipole-dipole forces
What properties of graphite are caused by its structure?
- very high melting point (it sublimes at over 3900K)
- conducts electricity (delocalised electrons aren’t attached to any particular carbon and are free to move along the sheets, so an electric current can flow)
- layers can slide over each other (weak intermolecular forces between layers are easily broken)
- insoluble in any solvent (covalent bonds in sheets are too strong to break)
Why is graphite less dense than diamond?
graphite is less dense than diamond as the layers are quite far apart compared to the length of the covalent bonds.
What are the uses of graphite?
- due to sheets being able to slide over each other, graphite feels slippery and is used as a dry lubricant and in pencils.
- used to make strong, lightweight sports equipment
What is graphene?
graphene is one layer of graphite.
What is the structure of graphene?
- a sheet of carbon atoms joined together in hexagons
- each carbon atom has 3 covalent bonds and one delocalised electron
- sheet is one atom thick (two-dimensional compound)
What are the properties of graphene?
- very high melting and boiling point
- insoluble
- best known electrical conductor (delocalised electrons are free to move and carry charge, without layers they can move quickly above and below the sheet)
- extremely strong (delocalised electrons strengthen covalent bonds between carbon atoms)
- single layer of graphene is transparent and very light
Due to its high strength, low mass and good electrical conductivity, what are potential uses of graphene?
potential applications in high-speed electronics and aircraft technology.
Due to its flexibility and transparency, what other uses of graphene are there?
touchscreens on smart phones and other electronic devices.
What is the structure of metal elements?
metal elements exist as giant metallic lattice structures.
How is a giant metallic lattice formed?
the electrons in the outermost shell of a metal atom are delocalised (free to move about the metal), leaving a positively charged metal cation e.g. Na+
Describe metallic bonding.
the positively charged metal cations are electrostatically attracted to the delocalised negative electrons. They form a lattice of closely packed cations in a sea of delocalised electrons.