c1 - atomic structure Flashcards
What does the periodic table show ?
-The periodic table shows us all the elements .
-There are over 100 elments .
What is an element ?
A substance made up of only one type of aotm .
What are compounds ?
Compounds contain two or more different elemnts chemically bonded .
-Combined in a fixed proportion .
Key fact about compounds .
Compounds usually have totally different properties from the elemts that theya re made from .
-If we want to separate a compound , back into its elemnts , we need to use a chemical reaction .
What is a mixure ?
We have different elemnnts or compounds which are not chemically combined togther
-If we want to sepearate a mixture , then we use physical techiniques rather than chemcil rections .
What is a molecule ?
A molecule has anyy elemnts chemically joined .
What does a chemical formula show ?
Tells us all the elents in a molecule and also the number of atoms in each eement .
-you cannot change the small number in a chemical formula as this producs a different molecule .
What is the law of conservation of mass ?
The total number of products formed in a reaction is equal to the total number of reactants .
Physical separations can be used to separate ?
Mixtures , but cannot be used for elements in a compound .
Gieva few examples of Physical separation techniques :
-Filitriation
Crystalisation .
-Distillation
-Chromatoraphy
When is fitiration used ?
Filtriation is used to separate an insoluble soild from a liquid .
(insoluble means solid won’t dissove in a liquid ) .
Conditions for filitration .
Solid and LIquid (check state symbolds)
-Need a filter funnel and filter paper .
Stage one of filitiration .
Pour mizure into filter paper .
-The liquid passes through the tiny pores in filter paper . (fitrate)
Stage two of filtiration .
HOwever solid material can’t pass through the filter paper and so is trapped . (residue)
-In the end liquid is separated form the soild .
When is crystalisation used ?
Used to separae a soluble solid from a liquid . Aqueous solution need (aq) check state symbols .
What is one way of doing crystalisation ?
-Leave the solution for a few days and water will evaporate leaving crystals of ur thing sodium chloride eg .
What to do if you want crysalisation to happen faster ?
-Heat the solution to evaportae out water .
-Bbe careful that the chemical we are trying to crystalise is not effected by the heating . Certain chemcials break down when heated .
What is simple distillation ?
Used to separate a liquid from a solid if we want to keep the liquid .
How does simple distialltion work ?
First we evaporate the liquid by heating ,
-We then condense the vapour by cooling
How does simple distillaiotn work ?
-Heat the solution
-vapour now rises up glass tube
-vapour now passes into the condeser (kept cold as cold water circulates the condseer ).
How does simple distillaton work (2) ?
-This mens vapour condenses turning vapour into a liquid .
-collect liquid in a beaker , Left with crystals of solid in a flask and liquid in a beaker .
What happens in fractional distilaiton ?
We sepeare a mixture of different liquids .
KEY POINT - these liquids must have different boiling points .
first stage of fractional distillation ?
1.Start by gently heaitng the mixtures .
second stage of fractional distillation ?
the liquids start to evaporate , But one with lower boiling point will evaporate more easily .
third stage of fractional distillation ?
When the vapours hit the fractonationg column , they condense and drip back into the falsk . The lquids hthen evaporate agaon .
fourth stage of fractional distillation ?
The repeated evaporation and cndensation increasing the amount of lower boiling point chemical in the fractonaitng column .
fifth stage of fractional distillation ?
As warm vapours pass up the coluumn they reach the thermoemter and temperature of it begins to rise .
-meaning a mixture of 2 different vapours are passing over the thermomeer .
sixth stage of fractional distillation ?
both vapours now pss into condenser and turn into a liquid .
-comes a point where temperature on thermoemter reaches bioling point of first chemical and it stops rising .
seventh stage of fractional distillation ?
now only one chemical in the condenser , so this is collected in a beaker .
eighth stage of fractional distillaiton
then the temperture rises agaom until reaches boiling point of second chemical , colect this in a second beaker .
What is the porblem if the liquids have very similar points in fractional distillation ?
-much harder to sepearte the liquids , might need multiple rounds of fractional distillaition .
fractional distillaiton to purifhy large volumes of lquid ?
-Sme principle but also requires different equipment . .
dra and label simple and fractional distillaiton .
check sheet .
How does paper chromatogrpahy do ?
Allows us to separate substances based on their dffierent solubilities .
first stage of papepr chromatogrpahy .
take a piece of chromatography paper .
-draw a pencil lne near th botom .
second stage of paper chromatogrpahy .
-put dots of our colours (substance) on a pencil line .
third stage of paper chromatogrpahy .
now put paper into solvent
(a liquid that will dissolve substances ).
fourth stage of paper chromatogrpahy .
The solvent now makes it way up the paper and dissolves the ink and coloured dots , which are also carried by the paper .
Why is paper in chromatography called stationary phase and the solven called mobile phase ?
Paper called stationary pahse as it does not move .
SOlvent called mobile pahse as it moves .
A pure compound …
will produce a sinlge spot in all solvent ,
a compound in a mixture (mixture of colours )
may sepearate into a different spots depending on the solvent .
More soluble substances…
travel further up the paper .
Why do we draw the starting line un pencil ?
As if we draw the line in pen , the pen ink would also move up with the solvent effecting the results
How to figure out unknown substance using chromatogrpahy .
-normal process of chromtogrpahy ,
measure the distance mvoed by the unkwon chemical (distance from pencil line to center of dot.)
-Measure the distancce moved by solvent .
Calcualtre rf calue distance moved by substance / distanced moved by solvent .
no untis .
look up in data base to find substance ,.
Rf value facts .
Several substacnes may have the same Rf calue , some may need to be repeated using a diffeent solvent .
If a substance has never been analysed before m ti willl have no rf value .
RQP for paper chromatogrpahy .
Sample of food chemicals ,
4 known food coloruings (a -d)
First stage pf paper chromatogrpahy rp ?
draw a hroizontal pencil line 2cm from the bootm of paper .
Second stage of paper chromatogrpahy rp ?
Mark five pencils pots at equal spaces acroos line .
-make sure there 1cm clear on each side of the paper .
Third stage of paper chromatogrpahy rp ?
use a capiallary tube to put a small spot of eak of the known colours and the unkown colours ontol pencil spot
fourth stage of paper chromatogrpahy rp ?
now pour waer into beaker depth of 1cm water in this case solven .
fifthstage of paper chromatogrpahy rp ?
attach a glass rod using tape and lower paper into a glass beaker ,bottom of paper should dip into water .
pencil line with psots must be above the surface of water why ?
or water will wash off the line .
the sides of the paper must not touch side walls why >
or it will interfere with the way water move s.
-Put a lid on beaker , to reudce the amount of evaporation of he solven t .
sixth stage of paper chromatogrpahy rp ?
at this stage water moeves up paper and colours are carried with it
remove paper when water travleld three quarters up it ,
-use a pencil to mark point how far water reached , Hang paper to dry .
where are the unkwon colours ..
the spots that line up with the unkwon colour is unkown colour .
what did greeks say atoms were ?
Atoms were tiny spheres that cannot be divided .
What happned in 1897 ?
Scientists discovered atoms contain tiny negative elexrons called electrons ,
-showed that atoms have an internal structure .
Came to the invention of plum puddign model - ball of possitive charge with embedded negative elctrons .
What did scientists do to see i the plum pudding model was correct ?
Did the alpha scateeirng experiment .
What happened in the alpha scattering experimen t .
-scientits took a piece of gold foil , gold used as it can be hammered into very thing foil .
-Then fire tiny positive alpha particles athe goild foil .
What was the first observation of alpha scattering model .?
-most atoms passed striaght thorugh gold foil without changing idrection .
-meant atoms were mostly empty space . .
What was the second observation of the alpha scattering model ?
-some alpha particles were deflced , changed direction when passin thorugh the gold foil ,
-meant the center of the atom must have a positive chtge , particles that came close to his are reppelled and changed direction .
what was the third observtion of the aplha scatering model ?
-some alpha particles bounced striaght off gold oil ,
-meant center of atom mst have a great deal of mass , center called nucleus ,
what did scienits do when they found reuslt of alpha scattering model ?
scientists replaced with nuclear model .
-empt space
-tiny positve nucleus
-around the egde , negative electrons .
What did Niels Bohr propose ?
He proposed electorns orbit the nucleus at specific distacnes , which was accepted by scienits .
-now call thse “orbits” energy levels /shells .
what happened several years after niels bohr .
-posiitve charge in nuclues so tiny positive particles called protons .
20 years after James CHadwick said nucles also contains neutrols .
soa toms have no overal chatge as number of protons is euqaal to number of electrons .
What is the radius of an atom.
1*power of minus ten .
what is the radius of a nuclues
1*ten to power of -14 .
stae relative mass and relatve charge of proton neutrol and electron .
check sheet .
What is the mass number ?
number of protons +neurons .
What is the atomic number ?
NUmber of portons which is equal to the number of electrons .
How do you work out the number of neutrons ?
Mass number - atomic number .
What are isotopes ?
-Isotopes are atoms of the same element with different number of neutrons .
-All atoms of an elemn have the same number of protons .
What are ions ?
Ions are atoms which have gained an overrall charge .
They have gained or lost electrons .
More about ions ?
Positiove ions have lost electrons .
Negative ions have gained electrons
(check sheet for an example ).
electrons exist in …
energy levels .
-each energy level holds a maximum number of electors .
1 st sheel holds two electrons
what does the second and third shell hold
what does the fourth shell hold ?
electrons .8 electrons
18
How do you work out wat group an elet is in by looking at the elctronic structure ?
the last number , if it is (2,6) last number shows it is in group 6 .
elements with full outer energy levels are found in …
group 0 , noble gases .
