atomic structure and the periodic table

atomic structure and the periodic table

1. separation techniques

   • chromatography
     • used to separate dyes and inks
       • 1. draw a line near the bottom of a sheet of filter paper do this in pencil -pencil marks insoluble, won't dissolve in solvent
         • 2. add spot of the ink to the line, place sheet in a beaker of solvent
           • 3. solvent used depends what's being tested, some compounds dissolve in water, some need ethanol
             • 4. make sure ink isn't touching solvent so doesn't dissolve into it
               • 5. put lid on container - prevent solvent evaporating
                 • 6. solvent seeps up paper, carrying ink with it. dye in ink will move up paper at different rates so dyes will separate out
   • filtration
     • used if separating insoluble solid from liquid mixture
       • use filter paper folded into cone shape, solid left in filter paper
   • evaporation
     • 1. pour solution into evaporating dish
       • 2. slowly heat the solution, the solvent will evaporate and the solution will get more concentrated. eventually crystals will start to form
         • 3. keep heating evaporation dish until you only have dry crystals left
   • crystallisation
     • 1. pour solution into an evaporating dish and gently heat solution. Some of the solvent will evaporate and the solution will get more concentrated
       • 2. once some of the solvent has evaporated or when you see crystals start to form (point of crystallisation) remove dish form the heat and leave the solution to cool
         • 3. the salt should start to form crystals as it becomes insoluble in the cold, highly concentrated solution
           • 4. filter the crystals out of the solution and leave them in a warm place to dry
   • simple distillation
     • used for separating out a liquid from a solution, e.g. water from sea water
       • 1. solution is heated, part of solution that has lowest boiling point evaporates first
         • 2. vapour then cooled, condenses and is collected, condensed by condenser - an outer glass tube filled with cold water that acts as "cooling jacket"
           • 3. the rest of the solution is left behind in the flask
   • fractional distillation
     • used to separate mixture of liquids, particularly if have similar b.p.
       • 1. put mixture in a flask and stick a fractionating column on top, then heat it
         • 2. the different liquids will have different b.p. so will evaporate at different temps
           • 3. liquid with lowest b.p. evaporates first, when the temp on the thermometer matches the boiling point if this liquid, it will reach the top of the column where there is a condenser
             • 4. liquids with higher b.p. might also start to evaporate but column is cooler towards top so will only get part of way up before condensing and running back down towards flask
               • 5. when first liquid has been collected you raise temp until next one reaches top

2. metals

   • metals on left in periodic table
   • metals are elements which can form positive ions
   • physical properties
     • all metals have metallic bonding which causes them to have similar basic physical properties
       • strong, but can be bent into shape - malleable
       • great at conducting heat and electricity
       • high melting and boiling points
   • transition metals
     • in centre of periodic table, are typical metals. good conductors, very dense, strong and shiny
     • properties
       • have more than one ion
       • often coloured and so compounds that contain them are colourful
       • make a good catalysts

3. group 1 elements - ALKALI METALS

   • soft, low density
   • down the group get more reactive, lower m.p. and b.p., higher relative atomic mass
   • react to form ionic compounds, generally white solids that dissolve in water to form colourless solutions
   • reaction with water
     • react vigorously to produce hydrogen gas and metal hydroxides- salts that dissolve in water to produce alkaline solutions
   • reaction with chlorine
     • react vigorously when heated in chlorine gas to from white metal chloride salts
   • reaction with oxygen
     • react with oxygen to form a metal oxide, different types of oxide will form depending on the group 1 metal
       • reactions with oxygen why group 1 metals tarnish in the air - they react with oxygen to form a dull metal oxide layer

4. group 7 elements - HALOGENS

   • flourine- very reactive poisonous yellow gas
     • chlorine- fairly reactive poisonous dense green gas
       • bromine- dense, poisonous red-brown volatile liquid
         • iodine- dark grey crystalline solid or purple vapour
   • exist as pairs of atoms

5. group 0 elements - NOBLE GASES

   • b.p. increases down group, due to increase in number if electrons leading ti greater intermolecular forces
   • full outer shell - very unreactive