BONDING< STRUCTURE< PROPERTIES OF MATTER Flashcards
can ions be groups of atoms
yes eg NO¬3-
describe how an ionic bond is formed
3 points
(a metal and non metal react)
metal loses outer electrons & forms + charged ion
non-metal gains outer electrons and forms - charged ion
oppositely charged ions are strongly attracted by electrostatic forces
(this attraction is called ionic bond.)
define ionic bond
the attraction between electrostatic charges of newly formed ions
name for positive ion
cation
name for negative ion
anion
why do atoms lose/gain electrons
to get the electronic structure of a noble gas
(- stable electronic structure)
elements in which groups most readily from ions
1,2,6,7
what do you need to include when drawing a dot and cross diagram for ionic bonding
4 things
only outer electrons
square brackets around the element symbol once they become ions
charge of ion
how many electrons are in each shell in brackets
eg (2,8)
4 things
what structure do ionic compounds have
giant ionic lattice structure
limitations of dot and cross diagram for ions x3
don’t show structure of ionic compound
dont show size of ions
dont show how ions are arranged
what is an ionic compound
a giant structure of ions
describe what an ionic compound is like inside.
4 points
-giant ionic lattice structure
-ions form closely packed regular lattice
- compound held together by strong electrostatic forces of attraction between oppositely charged ions.
(this is ionic bonding)
-these forces act in all directions in the lattice
what are limitations of ball and stick /
2d/3d diagrams of ionic compounds
ball and stick-
-model isn’t to scale
-in reality there arent gaps between ions
2/3d diagrams
-only see outer layer of compound
-not to scale
- no info about movement of electrons to form ions
2d
doesnt show where ions are located on other layer
4 properties of ionic compounds
-high melting point
-high boiling point
-cant conduct electricity when solid
-can conduct electricity when melted or dissolved(in water)
why do ionic compounds have high melting/ boiling points
why do ionic compounds conduct electricity when melted/ dissolved in water
large amounts of energy needed to break the strong bonds between ions
melted/ dissolved- ions are free to move, so they’ll carry an electric charge
dissolved- ions separate, free to move in solution
example of a crystal that is one giant ionic lattice
sodium chloride (table salt)
how do you work out empirical formula from a 3d diagram and then from a dot and cross diagram
3 steps
remember in test to put working out on page/reasoning
work out what ions are in compound
work out what charges the ions will form
balance the charges so the charge of the empirical formula is 0
eg. potassium forms 1+ ion
oxygen forms 2- ion
need 2 potassiums to balance out the 2- charge of Oxygen
empirical formula is K¬2O
- for dot and cross, count number of atoms of each element
covalent bonds are made when…
the + charged nuclei of the atoms attracted to the shared pair of electrons by electrostatic forces
this makes the covalent bonds strong
where does covalent bonds happen
in compounds of non metals and
in non metal elements
limitation of dot and cross diagram for covalent bonds
don’t show:
relative size of atoms
and
how atoms are arranged in space
limitations of displayed formula of covalent bonds
eg
H-N-H
a positive is it shows how atoms are arranged in large molecules
don’t show:
3d structure of molecule
or
which atoms the electrons in the covalent bond have come from
limitations of 3d model of covalent bonds x2
- gets confusing for large molecules
- don’t show where electrons in bonds have come from
how to find molecular formula of a simple molecular compound
count up how many atoms of each element there are eg C¬2H¬6
chemical formula for:
hydrogen
chlorine
oxygen
nitrogen
hydrogen chloride
methane
water
ammonia
* you need to be able to draw dot n cross for all of them
H¬2
Cl¬2
O¬2
N¬2
HCl
CH¬4
H¬2O
NH¬3
what type of structures do substances containing covalent bonds usually have
simple molecular structures eg O¬2, CH¬4
what are the properties of simple molecular substances
5 points
-atoms in a molecules held together by strong covalent bonds
(eg strong covalent bonds between 2 Oxygen atoms in a molecule of oxygen)
-weak intermolecular forces
(forces of attraction between molecules eg an O¬2 and another O¬2 molecule are weak )
-low melting and boiling points
-gas/liquid at room temp
-dont conduct electricity
what happens to bp and mp of simple molecular substances as the molecules get bigger. why
strength of intermolecular forces increases, more
energy needed to break the forces, mp and bp increase
why do simple molecular compounds/small molecules not conduct electricity
they are’nt charged, no free electrons/ions
explain how atoms are held together in a molecule of hydrogen chloride (covalently bonded)
a pair of electrons shared between atoms.
atoms held together by strong attraction between shared pair of - charged electrons and + charged nuclei of atoms
what are atoms in polymer molecules joined by
strong covalent bonds
describe the intermolecular forces between polymer molecules
intermolecular forces relatively strong-
stronger than in simple covalent,
weaker than ionic and covalent bonds
what are polymers at room temp
solid
when drawing the repeating unit of a polymer, what does the (…)n represent?
how do you find the molecular formula of a polymer
n - large number, unit repeated lots of times
- look at the repeating unit.
-write down molecular formula from that
-put in brackets.
-add n at the end
describe the molecules in in polymers.
describe what a polymer is
very large molecules
-small units linked together, forms long molecule with repeating units/sections
describe how atoms are bonded in a giant covalent strucutre
all atoms bonded to eachother by strong covalent bonds
three main examples of giant covalent structures
graphite
diamond
silicon dioxide (silica)
properties of giant covalent structures
and why
x2
high melting and boiling point
-lots of energy needed to overcome strong covalent bonds
don’t conduct electricity
- no charged particles
what is an allotrope
different structure of same element in same state
describe structure of diamond
x1
-each carbon atom has 4 covalent bonds with others
describe structure of graphite
x4
each carbon atom covalently bonded to three others
- layers of hexagonal rings
- no covalent bonds between layers
- one electron from each carbon atom is delocalised
properties of diamond
x3
-really hard due to 4 covalent bonds
-high melting point
-doesnt conduct electricity
properties of graphite
x3
-soft and slippery
-high melting point
-conducts electricity + thermal energy
why is graphite soft and slippery
what is graphite ideal for?
why does graphite conduct electricity
-no covalent bonds between layers
-layers held together weakly
-layers free to move over eachother
* ideal as lubricating material
-each carbon atom has one delocalised electron
what is graphene
(sheet of graphite)
-sheet of carbon atoms joined together in hexagons
properties of graphene x4
-one atom thin (2d)
-strong due to covalent bonds
-light
-conduct electricity
why is graphene useful
light- added to composite materials to improve strength without weight
conduct electricity through whole structure- useful in electronics
allotropes of carbon
diamond
graphene
graphite
fullerene
what are fullerenes
what was the first to be discovered and what was its shape
they are molecules of carbon with hollow shapes- (closed tubes/hollow balls
buckminsterfullerene- C¬60 -a sphere
describe structure of fullerene
made of carbon atoms arranged in hexagons -6 atoms or also (pentagons) 5 atoms (heptagons) 7 atoms
uses of fullerenes x4 and why x2
-to cage molecules- to deliver drug into body
why- forms around molecule and trap it inside
-industrial catalysts
why- large sa. so other catalysts can attach to the fullerenes
lubricant
strengthening materials
what is a carbon nano tube
cylindrical fullerene with high length to diameter ratio
what are carbon nanotubes useful for x3
nanotechnology ( technology that uses small particles)
electronics
materials- strengthen material without adding weight
properties of nanotubes
x3
-high length to diameter ratio
-conduct electricity and thermal energy
-high tensile strength
metals consist of….
giant structures of atoms arranged in a regular pattern
describe the metallic bonding in metals and structure
-electrons in outer shells are delocalised
- free to move through strucutre
-strong electrostatic attraction between + metal ions and the sea of delocalised - electrons
-this force is a metallic bond
-strong metallic bonds hold atoms in REGULAR STRUCTURE
substances held together by metallic bonds include….
ALL the properties of metals are due to….
elements and alloys
delocalised electrons (in metallic bonds)
describe mp and bp of metals + why
what are most metals at room temp
- high mp and bp
-metals have giant strucutre of atoms with strong metallic bonds (between metal atoms and sea of delocalised electrons)
-need alot of energy to break
solid
are metals good conductors of electricity and heat? explain
-delocalised electrons carry electric charge and thermal energy
- through whole structure
- good conductors
describe atoms in pure metals and effect of this
-atoms arranged in layers(that can slide over eachother)
-means metals can be bent and shaped ( malleable )
properties of metals x3
malleable
good conductors
high melting/boiling point
what are alloys
why are they made
a mixture of: 2 or more metals/ metal and another element
pure metals too soft for many uses. alloys are harder and more useful
why are alloys harder than pure metals
3 points
-different elements have different size atoms.
-layers distorted when pure metal mixed with another element
- layers can’t slide over eachother
The amount of energy needed to change state depends on ………
this then depends on
the strength of the forces between the particles of the substance.
the material, temperature, pressure.
describe particles in solid
4 points
- strong forces of attraction keeps particles
-close together in fixed positions in a
-lattice arrangement - solid has set shape and volume (as particles dont move)
-vibrate in fixed positions- more when solid is hotter
(causing solids to expand when heated)
describe particles in liquids
4 points
-weak forces of attraction
-randomly arranged and free to move
-tend to stick closely together
-fixed volume, not shape ( will flow to fill bottom of container)
-constantly move in random motion- faster when liquid hotter
(liquids expand slightly when heated)
describe particles in gases
4 points
- weak forces of attraction
- particles free to move + are far apart
-travel in straight lines - no definite shape/ volume (fill any container)
-constantly move in random motion- faster when gas is hotter
( when heated, gases EITHER expand / pressure increases
limitation of simple model of atoms in gas, liquid, solid
x3
-there are no forces in model ( so don’t know how strong they are)
-all particles represented as spheres
-spheres are solid.
describe how solid becomes liquid and liquid becomes gas
solid/liquid heated
particles gain energy
vibrate more / faster
forces that hold solid/liquid are weakened/ broken
at melting point/ boiling point particles have enough energy to break free from position/ break bonds
change state to liquid/gas
describe how gas becomes liquid and liquid becomes solid
gas / liquid cools and particles don’t have enough energy to overcome forces of attraction
bonds form/ more bonds form
at BP, so many bonds formed that gas becomes liquid- condensing
at MP, so many bonds form that particles held in place- liquid becomes solid- freezing
nanoscience works with nanoparticles of what size
what is size of reular atoms
1 to 100 nm diameter
-few hundred atoms
1x 10¬-10 metres
size of coarse particles
another name for coarse particles
size of fine particles
1 x 10¬-5 m and 2.5 x 10¬-6 m
aka dust
100 and 2500 nm
what happens to s.a to vol ratio when size of atom decreases
if side of cube decreases by factor of 10, what happens to s.a to vol ratio
s.a to vol ratio increases as size decreases
side of cube decreases by factor of ten, s.a to vol ratio increases by factor of ten
whats special about nanoparticles and explain
3 points
high s.a to vol ratio
properties of material different depending on if its a nanoparticle or in bulk
smaller quantities needed to be effective than materials with normal particle size
uses of nanoparticles
x6
medicine- tiny so absorbed easily- deliver drugs right into cells
electronics- if the material conducts, used in tiny electric circuits for computer chips
cosmetics-improve moisturiser w/out making it oily
suncreams
deodrants
catalysts=large sa to vol ratio
(+clothes)
disadvantages of using nanoparticles
x3
-the effects on health not yet properly investigated.(some believe nanoparticle products should be clearly labelled)
- not clear if they get into body and damage cells- (Modern nanoparticulate materials have only common recently,hard to determine risks)
-when washed away / thrown away - may damage environment- eg silver nanoparticles may harm or kill useful bacteria in the environment
why are nano particles used in suncreams
x2
better than traditional suncreams at protecting skin from harmful UV
better skin coverage
why are nanoparticles used in medicine
2 main points
-tiny so absorbed easily, deliver drugs right into cells
-silver nanoparticles have antibacterial properties.
added to polymer fibres, then used for masks/ wound dressings
