topic 2 recap Q. structure and bonding Flashcards
What is a covalent bond?
a shared pair of electrons
which type of atoms form covalent bonds?
non-metals
why do simple covalent substances not conduct electricity?
do not have delocalised electrons.
describe the structure and bonding of small molecules
small molecules with strong covalent bonds between the atoms and weak intermolecular forces between molecules
what is an ion?
an atom that has lost or gained electrons
what charges do ions from group 1 and 2 form?
+1
+2
why do small molecules have low melting points?
only a small amount of energy is needed to break the weak intermolecular forces
what charges do ions from group 6 and 7 form?
2-
1-
name the force that holds oppositely charged ions together?
electrostatic forces of attraction
which kinds of elements form ionic bonds?
metals and non-metals
describe the structure of a giant ionic lattice?
alternating positive and negative ions, held together by the electrostatic force of attraction
why do ionic substances have high melting points?
the electrostatic force is strong and needs alot of energy to break
why dont ionic substances conduct electricity when solid?
ions are in a fixed position so cannot move, and there are no delocalised electrons
when can ionic substances conduct electricity?
when melted or dissolved
why do ionic substances conduct electricity when molten or dissolved?
ions are free to move and carry charges
describe the structure of a pure metal?
strong electrostatic forces of attraction between metal ions and delocalised electrons
describe the bonding of a pure metal
layers of positive metal ions surrounded by delocalised electrons
what are the four properties of pure metals?
malleable
high melting/boiling point
good conductors of electricity
good conductors of thermal energy
explain why alloys are harder then pure metals
different sized atoms disturb the layers which prevents them from sliding over each other
explain why pure metals are malleable
layers can slide
explain why metals have high melting and boiling points
electrostatic forces of attraction between positive metal ions and delocalised electrons is strong
why are metals good conductors of electricity?
delocalised electrons are free to move and carry charge
why are metals good conductors of thermal energy?
delocalised electrons are free to move and transfer thermal energy
what is an alloy?
a mixture of a metal with another element
describe the structure and bonding of a giant covalent substances
billions of atoms bonded together by strong covalent bonds
describe the structure and bonding of polymers
many identical molecules joined together by strong covalent bonds in a long chain, with weak intermolecular forces between the chains
why do giant covalent substances have high melting points
it takes alot of energy to break the strong covalnt bonds
explain why graphite is soft
layers are not bonded so they can slide over each other
why do large molecules have higher melting and boiling points than small molecules?
the intermolecular forces are stronger
why do most covalent substances not conduct electricity?
they do not have delocalised electrons or ions
describe the structure and bonding in graphite?
each carbon atom is bonded to 3 others in a hexagonal ring arranged in layers.
each atom delocalises one electron and the forces between layers are weak
why can graphite conduct electricity
1 delocalised electron per carbon
what is graphene
one layer of graphite
give two properties of graphene
strong
conducts electricity
what is fullerene?
hollow cage of carbon atoms arranged in a sphere or tube
what is a nanotube?
hollow cylinder of carbon atoms
how big are nanoparticles?
1-100 nm
give two properties of nanotubes
high tensile strength
conduct electricity
how are nanomaterials different from bulk materials?
nanomaterials have a higher surface area-to-volume ratio
what is the relationship between side length and surface area-to-volume ratio?
as the side length decreases by a factor of 10 the surface area-to-volume increases by a factor of 10
what are nanoparticles use for?
healthcare
electronics
cosmetics
catalysts
how big are fine particles?
100-2500 nm
give 3 uses of fullerenes
lubricants
drug delivery
electronics
how big are course particles?
2.5 x 10-6 to 1 x 10-5
