ATOMIC STRUCTURE AND PERIODIC TABLE - need to do nuclear model onwards Flashcards
an element-
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-how many are there-
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an atom is-
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compound-
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-properties of compounds compared with of its elements
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-how to separate a compound
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mixture-
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-how to separate a mixture
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-what happens to properties of each substance in a mixture
molecule-
-element consists of atoms with same atomic number- all the same atoms
-about 100
-the smallest part of an element that can exist
-compound- 2 + different elements chemically combined in a fixed proportion
-compounds usually have totally different properties to the elements they’re made from
-only separated into elements by chemical reactions
-2+ different elements / compounds not chemically combined
-separated by physical processes
-unchanged
-molecule- any element chemically combined eg o2
-chemical reactions involve….
-physical process to separate a mixture x 5
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-do they involve chemical reactions
-are new substances made
formation of one or more new substances and often a detectable energy change
-filtration-insoluble solid from liquid
-crystalisation-soluble salt from liquid
-simple distillation-soluble solid + liquid
-fractional distilation-2 liquids w/ missible b.p’s
-chromotography
NO
how to do a filtration- 4 steps
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-crytalisation / evaporation done if….
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-evaporation done if-
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.how to do crystalisation
4 steps.
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-how to do evaporation-
3 steps
-filter paper folded cone shape- put in funnel
-pour mixture
-liquid and any dissolved substance passes through
-insoluble solid left
-the salt is aqueous-can be dissolved
-salt doesn’t decompose when heated
-pour solution in evaporating dish
-gently heat- solvent evaporates, solution becomes concentrated
-when some solvent evaporates/crystals start forming, remove dish from heat, let solution cool
-filter the crystals and leave them in warm place to dry/ drying oven/ desiccator/pat dry w/ filter paper
-pour solution in evaporating dish
-heat solution gently , solvent evaporates, solution becomes concentrated
-keep heating till left w/ dry crystals
-pro of evaporation
-what can you use to heat the solution
-how does the state symbol of the salt change after crystallisation/ evaporation
-quicker than crystalisation.
-bunsen burner- water bath- electric heater
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-goes from (aq) to (s) as its no longer dissolved in liquid
simple distillation used to separate…
simple distillation steps x5
liquid from solution if we want the liquid
-heat solution to evaporate liquid
-vapour runs through tube surrounded by condenser
-cold water running through condenser
-vapour cooled and condenses and collected in beaker
-rest of solution left in flask- may be as crystals
what happens when seawater undergoes simple distillation
-why isn’t distillation used to get drinking water
-problem with distillation
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-water evaporates and condenses- we get pure water
-salt left in flask
-alot of energy needed for simple distillation
-only use it to separate things with very different boiling points, if temp goes higher than b.p of substance w/ higher bp, they will mix again
what is fractional distillation used
-what is the set up for fractional distillation
-why is this important
mixture of liquids with miscible b.p’s (close but different)
-flask containing mixture connected to fractionating column (long column w/ hundreds of glass rods)
-cooler at top
-glass rods- high s.a
process of fractional distillation
#1- lowest bp liquid
#2-mid bp liquid
#3- highesr bp liquid
-heat to bp of #1
-#1 and some #2 and #3 will evaporate
-#1 vapour passes into condenser- condenses into beaker
- as #2 and #3 go up column its cooler. they come in contact w/ glass rods that are cooler than their bp
- #2 and #3 condense
-repeat, heat to bp of #2
-#2 condenses into empty beaker
-now can assume only thing left in flask is #3
-or heat to bp of #3 and let it condense into empty beaker
Chromatography used to separate….
-process - 6 steps
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.why do you see different spots
separate substances based on different solubilities
-draw pencil line on chromatography paper - near bottom
-put dot of first colour on pencil line and dot of second next
-place bottom of paper in solvent- make sure solvent doesn’t touch ink
-put lid on to stop solvent evaporating
-solvent makes its way up paper dissolves ink in coloured dots
-ink is carried up paper as well
-when solvent front is at almost at top of paper, remove paper+ let dry
-each dye in ink will move at different rate- dyes will separate out- each dye will form spot in 1 place
why do we draw starting line in pencil
-why should ink spot not touch solvent
pencil marks are insoluble- won’t dissolve in solvent
-don’t want spot to dissolve into solvent
what solvents can be used
Rf value =
depends on what’s being tested- some compounds dissolve well in water-
other solvents- eg ethanol - may be needed
-distance moved by substance / distance moved by solvent
no unit…
-what is the solvent front
-how do you measure distance moved by chemical
-point the solvent has reached up the paper
-from pencil line to centre of spot
what is the stationary phase
what is mobile phase
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how to tell if a colour is pure
how to tell if a colour is a mixture
the paper, it does not move
solvent is the mobile phase as it moves
- (a pure compound) will produce a single spot in all solvents
-compounds in a mixture may separate into different spots depending on the solvent used
why does paper chromatography work
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how to identify an unknown substance
different substances have different solubilities . A more soluble substance travels further up the paper than a substance that is less soluble. That way we can seperate substances based on solubility
-workout Rf value and compare to datatbase
if 1+ substances have this Rf value than compare it in other solvents
(if substance never analysed bfor, rf value x be on database)
-if any dyes in the ink are insoluble in the solvent they will….
-what would happen if you used pen to draw starting line
they’ll stay on the baseline
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-components in ink will separate out along with substance your analysing
-before electron discovered, ppl thought atoms were
-whose model was this
-tiny spheres that couldn’t be divided into smaller parts
-Dalton model
plum puddding model suggests the atom is
-why was this model made
sphere of positive charge with negative electrons embedded in it
-electrons were discovered
ALPHA SCATTERING EXPERIMENT
what did Rutherford and Marsden expect to happen
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-what did they do
-what happened
-expected particles to pass through or slightly deflected- +ve charge of atom counteracted by -ve electrons so overall neutral charge of atom
-fired +ve charged alpha particles (tiny particles) at thin sheet of gold foil
-most passed straight through
-some deflected
-some bounced/ deflected backwards
results from scattering experiment led to conclusion that-
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how did they come to this conclusion
mass of atom concentrated at centre- nucleus- and the nucleus was charged
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-most went straight through, so atom is mostly empty space
-some deflected- alpha particles with + charge repelled by concentrated + charge of nucleus
-some bounced back, directly striked the nucleus- centre of atom has a lot of mass
the alpha scattering experiment led to which model- describe it
-the nuclear model
most of atom empty
-positive nucleus at centre-mass of atom
-negative electrons around edge
who adjusted the nuclear model
-how
-why was it accespted
niels bohr
suggests electrons orbit the nucleus at specific distances (now energy levels)
-theoretical calculations agreed with others experimental observations
