bonding, structure and the properties of matter Flashcards
briefly describe each type of strong chemical bond
- ionic bonding; the particles are oppositely charged ions
- covalent bonding; the particles are atoms which share pairs of electrons
- metallic bonding; the particles are atoms which share delocalised electrons
what does each type of strong chemical bond occur in
- ionic bonding; occurs in compounds formed from metals combined with non-metals
- covalent bonding; occurs in most non-metallic elements and in compounds of non-metals
- metallic bonding; occurs in metallic elements and alloys
how are ionic bonds formed
when a metal atom reacts with a non-metal atom, electrons in the outer shell of the metal atom are transferred. the metal atoms lose electrons to become positively charged ions, while the non-metal atoms gain electrons to become negatively charged ions. the positive and negative metal and non-metal ion now experience an electrostatic force of attraction which forms the strong ionic bond
what happens after ionic bonding
the ions produced by metals in group 1 and 2 and by non-metals in group 6 and 7 have the electronic structure of a noble gas (full outer shell)
how can you represent ionic bonding
dot and cross diagram (either drawing the full electronic configuration or by just writing the element e.g. Na and displaying the dots and crosses of only the outer shell)
what does the charge on the ions produced by metals and non-metals relate to
the group number of the element in the periodic table e.g. Na forms Na¹⁺, meaning it is in group 1
what are ionic compounds
giant ionic lattices which have a regular closely-packed ion arrangement
how are ionic compounds held together
ionic compounds are 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 models can be used to represent ionic compounds
dot and cross diagrams, 3d models and ball and stick models
pros and cons of dot and cross diagrams for ionic compounds
PROS:
- they are useful for showing how ionic compounds are formed
CONS:
- they don’t show the structure of the compound
- they don’t show the relative sizes of the ions or how they are arranged
pros and cons of 3D diagrams for ionic compounds
PROS:
- they show the relative sizes of ions and the regular pattern
CONS:
- they only let you see the outer layer of the compound
pros and cons of ball and stick diagrams for ionic compounds
PROS:
- they show the regular pattern in an ionic lattice
- they show how the ions are arranged
- they show how the crystal extends beyond what is shown
- they show the relative sizes of the ions
CONS:
- they suggest that there are gaps between ions when, in reality, there aren’t
- they show the ions as solid spheres which they are not
why do ionic compounds have high melting and boiling points
due to the strong electrostatic forces of attraction between the oppositely-charged ions which act in all directions. these take a large amount of energy to overcome and break the many strong bonds
when do ionic compounds conduct electricity
they don’t conduct electricity when solid, but do conduct electricity when molten or dissolved in aqueous solution
why do ionic compounds only conduct in certain conditions
when solid, the electrostatic forces of attraction hold the ions in fixed positions so they cannot move. when molten or dissolved in aqueous solution, ions are free to move and carry charge throughout the structure
3 main properties of ionic compounds
- high melting and boiling points
- soluble in water
- conduct electricity when molten or dissolved in aqueous solution
how are covalent bonds formed
when a pair of electrons is shared between two non-metal atoms. both atoms end up with one extra electron in their outer shell. the positively charged nuclei of the atoms are attracted to the shared pair of electrons by electrostatic forces, making covalent bonds very strong
what can covalently bonded substances be
- very large molecules e.g. polymers
- giant covalent structures e.g. diamond
- small molecules e.g. hydrogen
what is the difference between electrostatic forces and intermolecular forces of attraction
- electrostatic forces of attraction are in ionic bonds and are between positive and negatively charged atoms
- intermolecular forces of attraction are in covalent bonds
what are small molecules
they’re made up of only a few atoms joined together by covalent bonds, and are usually gases or liquids that have relatively low melting and boiling points
why do small molecules have low melting and boiling points
they have very weak intermolecular forces of attraction between the molecules which require very little energy to overcome, hence they have low melting and boiling points; hence they are mostly gases or liquids at room temperature
why do small molecules not conduct electricity in any state
because the molecules do not have an overall electric charge as there are no ions and no delocalised electrons, so they cannot carry charge
what happens as the size of the small covalent molecule increases
the melting and boiling points also increase because as molecules get bigger, the intermolecular forces strengthen, so more energy is required to overcome them
you need to overcome the strong covalent bonds between atoms within small molecules to melt or boil it (T/F)
FALSE, you have to overcome the intermolecular forces
properties of small molecules
- low melting and boiling points
- very weak intermolecular forces of attraction
- don’t conduct electricity
difference in ions between giant covalent structures and giant ionic lattices
giant covalent structures (otherwise known as macromolecules) are similar to giant ionic lattices but have no charged ions
why do giant covalent structures have very high melting and boiling points
to melt or boil giant covalent structures, you need lots of energy to overcome all of the many strong covalent bonds between atoms. for this reason they are solid at room temperature
examples of giant covalent structures
diamond, graphite, silicon dioxide
examples of small molecules
hydrogen, chlorine, methane
properties of giant covalent structures
- no charged ions
- strong covalent bonds
- high boiling and melting points
what do metals consist of
giant structures of atoms arranged in a regular pattern
how are metallic bonds formed
the electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole structure and carry charge. the sharing of delocalised electrons gives rise to strong metallic bonds
why do metals have high melting and boiling points
there are strong electrostatic forces of attraction between the negatively charged sea of delocalised electrons and the positive metal ions, which require lots of energy to overcome. this means that most metals are solid at room temperature
why can metals conduct electricity
the sea of delocalised electrons are free to move and carry charge throughout the structure
what does the state that a material is in depend on
the strength of the forces of attraction between particles of a material. the strength of the forces between particles depends on:
- the material; the structure of the substance, the types of bonds holding the particle together
- the temperature
- the pressure
limitations of the simple model for the states of matter
- forces of attraction between particles are not shown
- all particles are represented as inelastic spheres
- it models particles as solids
particle theory of a solid
- very strong forces of attraction between particles which hold particles close together in fixed positions to form a very regular lattice arrangement
- the particles do not move from positions, so solids have a definite shape and volume; they don’t flow
- the particles vibrate on the spot and as temperature increases, particles vibrate faster
particle theory of a liquid
- there are relatively weak forces of attraction between particles, so particles are randomly arranged and are free to move around each other, but remain in contact with one another
- have a fixed volume but not a fixed shape and will take the shape of the container they are in
- the hotter a liquid gets, the faster the particles move around each other
particle theory of a gas
- forces of attraction between particles are very weak, hence particles are free to move in a random, rapid motion
- particles travel at different speeds but in straight lines
- particles collide with each other and with the sides of the container
- gases do not have a fixed shape or a fixed volume and will always fill any container
- as temperature increases, the faster particles move and the more frequently (and with more energy) they hit the walls of the container, causing the gas pressure to increase or the volume to increase if the container is not sealed
what are polymers
they have very large molecules in which the atoms are linked to other atoms by strong covalent bonds
what state are polymers at room temperature and why
they’re solids at room temperature because of the relatively strong intermolecular forces between polymer molecules which require a lot of energy to overcome
describe the structure of pure metals and explain what properties this gives
in pure metals, the atoms are arranged in layers which can easily slide over each other, allowing metals to be bent and shaped. this also makes metals soft and malleable
what is an alloy
a mixture of metals and other elements that are harder and more useful than pure metals
why are alloys formed
because pure metals are too soft for many uses
how are alloys harder than pure metals
different elements have different sized atoms so, when another element is mixed with a pure metal, the regular layers are distorted, meaning that they cannot easily slide over each other – hence alloys are harder than pure metals
what are metals good conductors for and why
- they’re good conductors of electricity because the delocalised electrons in the metal are free to move and carry electrical charge through the structure
- they’re good conductors of thermal energy because energy is transferred by the delocalised electrons
define an allotrope
a different structural form of the same element in the same physical state of matter
the main allotropes of carbon
diamond, graphite, graphene and fullerenes
describe the structure of diamond
it’s a giant covalent structure in which each carbon atom forms four covalent bonds with adjacent carbon atoms; this forms a very rigid structure as the strong covalent bonds fix atoms in place, making diamond very hard
properties of metals
- good conductors of electricity and thermal energy
- soft and malleable
- arranged in layers which can easily slide over eachother
- high melting and boiling points
why does diamond have a very high melting point
just like any other giant covalent structure, it has many strong covalent bonds acting in all directions between the carbon atoms which requires a lot of energy to overcome
why does diamond not conduct electricity
because each carbon atom bonds to 4 other carbon atoms, so all electrons are being used for bonding, meaning none are delocalised
properties of diamond
- each carbon atoms forms four covalent bonds
- very high melting point
- cannot conduct electricity
- giant covalent structure
- very hard due to rigid structure
describe the structure of graphite
each carbon atom forms three covalent bonds with three adjacent carbon atom, forming layers of hexagonal rings which have no covalent bonds between the layers. instead, the layers are held together by weak intermolecular forces
what can graphite conduct and why
- it can conduct electricity because only 3 out of 4 outer electrons are used in bonding, so each carbon atom has one delocalised electron which is free to move and carry charge throughout the structure
- it can conduct thermal energy because the delocalised electron transfers energy
why does graphite have a high melting point
because the covalent bonds within the layers require a lot of energy to overcome, despite graphite having weak intermolecular forces between the layers
why is graphite soft and slippery
as there are only weak intermolecular forces between the layers, they can easily slide over each other, making graphite soft and slippery; it is ideal as a lubricating material
properties of graphite
- each carbon atom is covalently bonded to three other carbon atoms
- forms layers of hexagonal rings
- no covalent bonds between the layers
- weak intermolecular forces between layers
- high melting point
- soft and slippery
- conductor of electricity and thermal energy
how is graphite similar to metals
they both have delocalised electrons
what is graphene
a single layer of graphite making it a 2D substance
why is graphene strong
due to the network of strong covalent bonds
why can graphene conduct
it contains delocalised electrons so can conduct electricity throughout the whole structure, making it useful in electronics
special feature of graphene
it is incredibly light, so can be added to composite materials to improve strength without adding much weight
properties of graphene
- single layer of graphite
- very strong network of covalent bonds
- incredibly light
- contains delocalised electrons
- can conduct electricity
what are fullerenes
molecules of carbon atoms with hollow shapes that can either be tubes or spherical
describe the structure of fullerenes
it is based on hexagonal rings of carbon atoms, in which each carbon atom is bonded to 3 other carbon atoms so they can conduct electricity due to delocalised electron. they may also contain rings with five or seven carbon atoms.
what are buckminsterfullerenes
the first fullerene to be discovered which is spherical in shape, forming a hollow sphere containing 20 hexagons and 12 pentagons. it has the molecular formula C₆₀
what are carbon nanotubes
small cylindrical fullerenes with very high length to diameter ratios. their properties make them useful for nanotechnology, electronics and materials; they’re good conductors of heat and electricity
uses of fullerenes (nanoparticles)
- in medicines for drug delivery
- as catalysts due to their large surface area
- as lubricants; there are no bonds between molecules so they are soft and reduce friction
- strengthening materials
- in electronics
what is nanoscience
the reference to structures that are 1 to 100nm in size
as the side of cube decreases by a factor of 10, what happens
the surface area to volume ratio increases by a factor of 10
why may nanoparticles have properties different from those for the same materials
because of their high SA:V ratio, with a high percentage of their atoms exposed at their surface
what can nanoparticles result in
smaller quantities being needed to be effective than for materials with normal particle sizes e.g. catalysts for industrial processes
why are new applications for nanoparticles important
they could improve many aspects of modern life
pros of nanoparticles
- they may catalyse reactions more efficiently
- they may catalyse different reactions
- nanocages of gold can be used to deliver drugs to where they need to go in the body e.g. carrying cancer-fighting drugs to the tumour
- they are used to reinforce materials e.g. sport -> making very strong but light tennis racquets
- can be used in sun-screens to block ultra-violet light
- can be used in face creams to deliver active ingredients deeper beneath surface of skin
uses of nanoparticles
- in medicine to deliver drugs in the body
- in electronics
- in cosmetics
- as sun creams
- as deodorants
- as catalysts
cons of nanoparticles
- nanoparticle sunscreens tend to clump together, making them difficult to apply
- it may be more difficult to tell where you have applied the sunscreen if you can’t see it on your skin
- toxic substances could bind to them because of their large SA:V ratios, harming health if the nanoparticles do get into the body
- breathing in the nanoparticles could damage the lungs
- nanoparticles could enter the bloodstream from their use in cosmetics, with unpredictable effects on our cells
- if a spark is made near a large quantity of the catalyst (nanoparticles), due to their large SA:V ratio, there could be a violent explosion
uses of silver nanoparticles
- antibactericides in fridges
- sprays in operating theatres
- wound dressings
- on clothes
pros and cons of silver nanoparticles
PROS:
- they inhibit the growth of microorganisms
- they can clean operating theatres in hospitals
- they can be used as antimicrobial coatings
CONS:
- these nanoparticles could enter the environment and affect aquatic life by accumulating in organisms over time
