chemistry topic 2


  • ions are made when electrons are transferred
  • if 2 electrons are lost the charge is +2
  • groups 1 elements form +1 ions, group 2 elements form +2 ions, group 6 forms -2 ions and groups 7 forms -1 ions
  • sodium is in group 1 so it loses 1 electron to form Na+, Na -> Na+ + e- 
  • chlorine is in group 7 so it gains 1 electron to form Cl-, Cl + e- -> Cl-
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  • ionic bonding is when a metal and a non metal react together, the metal atom loses electrons to form positively charged ions and the non metal gains electrons to form negativley charged ions, these oppositely charged ions are strongly attracted to one another by electrostatic forces, this attraction is called an ionic bond
  • dot and cross diagrams shows the arrangemt of electrons in an atom or ions, each electron is represented by a dot or a cross
  • dot and cross diagrams are useful for showing how ionic compounds are formed but they dont show the structure of the compound, the size of the ions or how theyre arranged
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  • ionic compounds have a structure called a giant ionic lattice which is in a regular pattern, there is a very song electrostatic forces of attraction between the oppositvely charged ions in all directions of the lattice
  • ball and stick models can be used to show the structure as its shows the arrangement, however the atoms are not to scale and in reality there arent any gaps in between the ions 
  • ionic compounds have high melting and boiling points due to the many strong bonds between the ions, it takes a lot of energy to overcome this
  • when they are solid the ions are held in place meaning the compounds cant conduct electricity  but when the ionic compound melts, the ions are free to move and carry an electric current
  • ionic compounds also dissolve easily in water, the ions seperate and are all free to move in the solution so they will carry electric current
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  • covalent bonding occurs between non metals, they share pairs of electrons to make covalent bonds
  • the positively charged nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forces making the covalent bonds very strong
  • you can use dot and cross diagrams to show the bonding in covalent compounds
  • electrons drawn in the overlap between the outer orbitals of the two atoms are the shared atoms
  • displayed formulas are good to show how atoms are connected in large molecules however they dont show the 3d structure
  • 3d models are useful however can get confusing with too many atoms
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  • simple molecular substances are made up of molecules containing a few atoms joined together by covalent bonds
  • hydrogen reacts together to form a single covalent bond
  • oxygen reacts together to form a double covalent bond
  • nitrogen reacts together to form a triple covalent bond
  • methane  can form four covalent bonds with its four hydrogen and one carbon
  • these atoms are held togehter with very strong covalent bonds. by contrast the forces of attraction between these molecules are very weak
  • the melting and boiling points are quite low as they do not require mch energy to break the intermolecular forces
  • most molecular substances are liquid or gas at rtp
  • as molecules get bigger the strength of the intermolecular forces increases meaning the melting and boiling point increase as more energy is required to break these forces of attraction
  • there are no free ions or electrons so they dont conduct electricity
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  • polymers are long chains of repeating units
  • the intermolecular forces between the polymer molecules are larger than between simple covalent molecules so more energy is needed to break them, this means most polymers are solid at rtp
  • the intermolecular forces are still weaker than ionix or covalent bonds so they generally have lower boiling points than ionic or giant molecular compounds
  • in giant covalent structures, all the atoms are bonded to each other by strong covalent bonds which they have a very high melting/boiling point. they dont conduct electricity as the contain no charged particles ( apart from graphite)
  • diamond- each carbo atom forms four covalent bonds in a rigid structure
  • graphite- each carbon atom forms three covalent bonds to create layers of hexagons. each carbo atom also contains a delocalised electron
  • silica/silicon dioxide- this is what sand is made up of, each grain of sand is a gaint structure of silicon and oxygen
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  • strong covalent bonds in diamond require a lot of energy to break which gives diamond a very high melting point
  • in graphite there is no covalent bonds between the layers, they are held together weakly so are free to slide over each other, this makes graphite soft and slippery so it makes a good lubricating material. the covalent bonds require high amounds of energy to break the bonds. the delocalised electron can carry charge meaning graphite conducts electricity
  • graphene is one layer of graphene which is very lightweight
  • fullerenes are molecules of carbon shaped like hollow balls or tubes. they are mainly arranged in hexagons and can be used to cage other molecules which makes it ideal for drug delivery, they also have a large surface area which can be used as an industrial catalyst
  • fullerenes can form nanotubes which can conduct heat and electricity, they are very strong  and are used in nanotechnology as they can strengthen without adding much weight
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  • metals consist of a giant structure, the electrons in the outer shell of the metal atoms are delocalised
  • there are strong forces of electrostatic attraction between the positive metal ions and the shared negative electrons, these forces of attraction hold together the atoms in a regular structure and are known as metallic bonding
  • most metals are soldi at rtp as the strong electrostatic forces require lots of energy to break
  • they are good conductors of heat/electricity due to the delocalised electrons
  • most metals are malleable as the layers in a metal can slide over each other
  • alloys are harder than pure metals because the different elements are of different sizes meaning the layers become destorted which makes them hard to slide over each other
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  • theres three states of matter- solid liquid gas
  • how strong the forces are depends on the material,the temp and the pressure
  • in solids there are strong forces of attraction between particles which holds them close together in a fixed position to form a regular lattice arrangement, the particles dont move so solids keeps a definiteshape and volume, they dont flow. the particles vibrate, when temp increases the particles vibrate more causing it to expand slightly
  • in liquids there is a weak force of attraction between the particles, they are randomly arranged and are free to move past each other, liquids have adefinite voolume but dont keeps adefinite shape, they with flow to fill the bottom of the container. these particles are constantly moving with random motion, the hotter the liquid gets the faster the particles move, they expand when heated
  • in gases the force of attraction is very weak, they are free to move and have no arrangement, the particles move in straight lines. gases dont have a definite shape or volume and will always fill any container. particles have random motion, they move faster when heated and also expand, pressure increase
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  • solid is heated -> more kinetic energy -> weaken the forces ->at melting point they break free -> this is called melting and turns solids into liquids
  • liquid is heated -> even more kinetic energy -> weakens the forces -> at boiling point they break free -> this is called boiling and turns liquids into a gas
  • gas cools -> no longer have energy to overcome forces -> bonds form at boiling point -> this is called condensing and turns gas into liquids 
  • liquid cools -> no longer have energy to overcome forces -> bonds are formed at melting point -> this is called freezing and turns liquid into solid
  • sublimation is the term where a solid misses a state and turns into gas and visa versa
  • you may be asked to predict what state a substance will be at a certain temp. if the temp is below the melting point, itll be a solid. if is above the boiling point itll be a gas. if is in between the two points then its a liquid
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  • coarse particles -> diameter between 2500nm and 10000nm and are called dust
  • fine particles -> diameter between 100nm and 2500nm 
  • nanoparticles -> diameter between 1nm and 100nm these particles only contain a few hundred atoms
  • the science that investigates nano particles is called nanoscience
  • nano particles have large surface area to volume ratio
  • surface area to volume ratio= surface area/volume
  • as partilces decrease in size the size of there surface area increases in relation to their volume. this causes the surface area to volume ratio to increase
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  • they have a large surface area to volume ratio meaning they  could help make new catalysts
  • nanoscience- the idea is that tiny particles such as fullerenes are absorbed more easily into the body meanig they could deliver drugs right into the cells that are needed
  • some nanoparticles conduct electricity so they could be used in tiny electrical circuits for computer chips. silver nanoparticles have antibacterial properties meaning they could be added to polymer fibres that are used to make surgical masks, would dressings and deodorants. nanoparticlesare also being used in cosmetics eg they are put in moisturisers without making them really oily
  • some people are worried about the risks on human health and the long term impacts. nanoparticles are being used in suncreams as they have been shown to be better at protecting our skin from harmful uv rays, also give better coverage
  • its not yet clear whether or not in the body the damage cells, its also possible that when theyre washed away they damage the environment
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