chemistry

• the nucleus is n the middle of an atom and contains protons and neutrons. due to this, it has a positive charge.
• proton= +1

  neutron= 0

  electron= -1
• protons:

  the number of protons are equal to the number of electrons.

  atoms are neutral and they have no overall charge. this is because they have the same number of protons as electrons meaning they cancel each other out.
• atomic number and mass number:

  -the nuclear symbol of an atom tells you its atomic (proton) number and mass number

  -the atomic number tells you how many protons there are

  -the mass number tells you the total number of protons and neutrons.

  -the get the number of neutrons just subtracts the atomic number from the mass number
• isotopes are different forms of the same element which have the same number of protons and different number of neutrons. so isotopes have the same atomic number but different mass numbers.
• compounds are substances formed from two or more elements, the atoms of each are in the fixed proportions throughout the compound and are held together by chemical bonds.
• ionic bonding: metal and non metal. Metal loses ions to gain a positive ions, Non metal gains ions to become negative ions.
• covalent bonding: 2 non metals that shares electrons
• mixtures have no chemical bond and can be separated easier than compounds.
• chromatography 6 marker?

  1. draw a line near the bottom of a sheet of filter paper
  2. add a spot of ink on the line and place the sheet in a beaker of solvent.
  3. the solvent depends on what's being tested. some compounds dissolve well in water but sometime may need other solvents
  4. make sure the ink isn't in the solvent
  5. put a lid onto to prevent solvent from evaporating
  6. the solvent seeps up the paper which carries the ink
  7. each dye will form a spot meaning there's more than 1 colour.
  8. if any of the dyes in this ink are insoluble they'll stay on the baseline.
• filtration: can be used if the product is an insoluble solid that needs to be separate from a liquid reaction mixture. it can also be used as purification as well.
• evaporation: pour the solution into an evaporating dish, slowly heat the solution. the solvent will evaporate and the solution will get more concentrated. eventually crystals will start to form. keep heating the evaporating dish until all you have.left is dry crystals.
• crystallisation: pour solution into an evaporating dish and gently heat the solution. some of the solution will evaporate and the solution will get more concentrated. once some of the solvent has evaporated, or when you see crystals start to form, remove the dish from the heat and leave solution to cool.
• distillation is used to separate mixtures which contains liquid. there are two types called simple distillation and fractional distillation.
• simple distillation is used for separating out a liquid from a solution. the solution is heated and the part of the solution that has the lowest boiling point will evaporate first. the vapour is then cooled, condenses and is collected.

  the problem of simple distillation is that you can only use it to separate things with very different boiling points.
• fractional distillation: is used to separate mixtures of liquids e.g. crude oil. you put a mixture in a flask and stick a fractionating column on top. then you have to heat it.

  the different liquids will have different boiling points. so they will evaporate at different temperatures.

  the liquid with the lowest boiling point evaporates first. when the temperature of the thermometer matches the boiling point of this liquid, it will reach the top of the column.
• J.J Thomson collided from his experiments that atoms weren't solid spheres. his measurements of charge and mass showed that an atom must contain even smaller negatively charged particles (electrons)

  he made a plum pudding model that showed the atom as a ball of positive charges with electrons stuck in it.
• Rutherford conducted the alpha particle experiment. this fired positively charged alpha particles at a thin sheet of gold. they expected the particles to pass straight through the gold but some deflected more than expected.
• Rutherford came up with the nuclear model of an atom. this had a tiny positively charged nucleus in the middle where most of the mass was concentrated.
• Bohrs nucleus model suggested that electrons orbited in shells. this was explained a lot through experiments and observations over time by other scientists.
• Mendeleev left gaps and predicted new elements....

  -put his elements in order of atomic weight but did switch the order if the properties meant it should be changed.

  -also put them in similar properties.

  -gaps were left in the table to make sure elements with similar properties stayed in the same groups.
• group number tells you the amount of electrons there are in the outer shell.
• metals:

  -elements which can from positive ions when they react.

  -found towards the bottom and to to the left of the periodic table.
• electronic structure of atoms:

  -metals to the left don't have many electrons to lose and metals towards the bottom of the table have outer electrons which are far from the nucleus (weaker attraction).

  -this means that not much energy is needed to remove the electrons.
• differences between non metal/metal properties?

  metals: strong, can be bent (malleable), conducted of heat/electricity, high boiling/melting point.

  non-metals: dull looking, brittle, aren't always solid at room temperature. don't generally conduct electricity, low density.
• group 0: noble gases that have 8 electrons in their outer shell which means they don't react with much at all.

  -colourless gases at room temperature

  -they're non-flammable.

  -boiling points increase as you move down the group.
• when metals form ions, they lose electrons from their outer shell to form positive ions.

  when non metals form ions, they gain electrons into their outer shell to form negative ions.
• what is ionic bonding?


  -is when a non-metal and metal react together. these are strongly attracted to one another by electrostatic forces.

  -dot and cross diagrams show the arrangement of atoms.
• ionic compounds have a regular lattice structure. this is called giant ionic lattice. the ions form a closely packed lattice arrangement and there are very strong electrostatic forces of attraction.
• ionic compounds properties:

  -they have high melting/boiling points due to strong bonds between ions (takes a lot of energy to overcome the attraction)

  -when they're solid, the ions are held in place so compounds can't conduct electricity. when these compounds melt, the ions are free to move and they'll carry an electric charge.

  -some ionic compounds dissolve in water.
• what is covalent bonding?


  when non-metal atoms bond together, they share pairs of electrons. this makes the bonds very strong.
• what are polymers?


  -is a lot of small units that link together to form long molecules that has repeating sections. all the atoms in a polymer are joined by strong covalent bonds.
• giant covalent structures are...

  -all atoms are bonded to each other by strong covalent bonds.

  -they have very high melting/boiling points as lots of energy is needed to break covalent bonds.

  -they don't contain charged particles so they don't conduct electricity.

  -diamond and graphite are made from carbon atoms only.
• diamond:

  -has a very giant covalent structure

  -made of carbon atoms that form 4 covalent bonds. (makes the diamond really hard)

  -these covalent bonds take a lot of energy to break and give diamond a very high melting point.

  -it doesn't conduct electricity because it has no free electrons.
• graphite:

  -each carbon atom only forms 3 covalent bonds creating sheets of carbon atoms arranged in hexagons.

  -there aren't any covalent bonds between the layers, they're only held together weakly so they're free to move over each other.

  -makes graphite soft and slippery so tends to be used as a lubricating material.

  -has a high melting point, as the covalent bonds in the layers need loads of energy to break

  -only 3 of 4 outer electrons are used in bonds so each carbon has one electron thats delocalised.
• metallic bonding involves delocalised electrons:

  -the electrons in the outer shell of metal atoms are delocalised (free to move around)

  -these are strong forces of electrostatic attraction between positive and shared negative electrons.
• solids: strong forces of attraction between particles which holds them in fixed positions from regular arrangement.

  -particles don't move

  -particles vibrate, the hotter the solid becomes the more they vibrate.
• liquids: have weak forces of attraction between particles. they're randomly arranged and free to move past but tend to stick closely together.

  -liquids have a definite volume but don't keep a definite shape

  -particles are constantly moving with random motion. the bottle the liquid gets, the faster they move.
• gases: the force of attraction between particles are very weak, they're free to move and are far apart.

  -travel in straight lines,

  -don't keep a definite shape or volume

  -the particles move constantly with random motion. the hotter the gas gets, the quicker they move.
• changing states:

  solid---->liquid = melting

  liquid -----> gas = boiling

  gas----> liquid = condensing

  liquid----> solid= freezing.