Topic 9 - Structure and bonding Flashcards
how is a covalent bond formed
when a pair of electrons is shared between two non-metal atoms to achieve a full shell
how is a ionic bond formed
when electrons are transferred from metal to non metals to produce metal cations and non metal anions
why do covalent bonds have strong forces of attraction
the pair of negatively charged electrons are attracted to the two positive nuclei through electrostatic forces
properties of simple covalent structures
- don’t conduct electricity
- low melting/ boiling points
why don’t simple covalent structures conduct electricity?
they have no ions or free electrons so there’s nothing to carry the electrical charge
why do simple covalent structures have low MP/BP?
- although the covalent bonds within the small molecules are strong
- molecules have weak intermolecular forces of attraction
- only intermolecular forces need to be broken down to melt/boil
- takes small amount of energy to overcome the intermolecular forces
what are giant covalent structures
made up of lots of atoms all bonded together by strong covalent bonds
properties of giant covalent structures
- high melting and boiling point
- doesn’t conduct electricity ( apart from graphite
- aren’t soluble in water
why do giant covalent structures have a high MP/BP
lots of energy needed to overcome the many covalent bonds holding the atoms together
- covalent bonds have strong forces of attraction
why don’t MOST giant covalent structures conduct electricity
they have no ions or free electrons so there’s nothing to carry the electrical charge
allotropes ( of carbon )
different structural forms of the same element
why is diamond hard and tough?
- each carbon atom forms 4 covalent bonds with other carbon atoms
- this forms a very rigid structure and the ions can’t slide over each other
why can’t diamond conduct electricity?
they have no ions or free electrons so there’s nothing to carry the electrical charge
why is graphite soft ?
-each carbon atom only forms 3 covalent bonds
- creates layers of carbon atoms arranged in hexagons
- no covalent bonds between layers so they easily slide over each other
why does graphite conduct electricity?
-only 3 of 4 outer electrons of carbon atoms are used in covalent bonding
-this leaves one electron that’s delocalised and can move
-these carries electricity
graphene
single layer of graphite
- very strong and light
uses of diamond
strengthen cutting tools, such as drill bits
uses of graphite
lubricating material, in pencils
uses of fullerenes
in medicine, catalysts, strengthening materials
properties of ionic substances
- high melting/boiling points
- dissolves in water easily
- only conducts electricity when molten or in solution
why do ionic substances have high MP/BP
- oppositely charged ions are strongly attracted to each other and
- this holds the ions in an ionic lattice
- it takes a large amount of energy to overcome the many strong bonds which have this attraction
why do ionic substances only conduct electricity when molten or dissolved ?
- when solid the ions are all held in fixed positions and can’t move
- when molten/dissolved the ions are free to move and carry electrical charge
properties of metals
- high melting and boiling points
- conduct electricity
-malleable - don’t dissolve in water
- high density
why do metals have high MP/BP?
- the electrostatic forces between the
positive metal ions and delocalised sea of electrons are very strong - lots of energy needed to overcome these forces
why do metals have conduct electrictiy?
- delocalised electrons which are free to move through whole metal
- much better at conducting electricity than most non-metals
why are metals mallaeble?
- consists of atoms held together in a regular structure
- form layers which are able to slide over each other
- they can be rolled in flat sheets
nanoparticles
really tiny particles that have diameter between 1nm to 100nm
10-1000 time bigger than atoms
