Chemistry Revision Unit 1


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  • Created by: keldra
  • Created on: 15-05-10 19:44


Relative Atomic Mass - the mass of an atom (isotopes) relative to carbon-12

Atomic Mass Unit - mass of carbon 12 atom divided by 12

Relative Formula Mass - sum of all the relative atomic mass of all atoms in a formula

Relative Molecular Mass - sum of all RAM in a chemical formula of a covalent compound

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Mass Spectrum (data produced by mass spectrometer)

1. Sample must be measured in a gaseous state to pass through the machine, it is then VAPOURISED.

2. Vapour is attacked by high energy electrons that collide with atoms. Particles now charged can be ACCELERATED into an electric field.

3. They are accelerated by the electric field.

4. Pass through a velocity sector (travelling at the same speed), differences in mass in the magnetic field will be to charge/size differences.

5. MF deflects them how much depends on the M/C (lighter ions deflected more). MF strength is increased only ions of a specific M:C then DETECTED

6. Detector how many ions pass through.

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Uses of MS (HSW)

Gives you the relative abundance of different isotopes

used in pharmaceuticals

it can measure small samples accurate

detect isomers

12-15 years to dvlp drugs.

HPLC High Performance Liquid Chromatography - chemicals injected into a steel rod filled with silica, separated as solvent passed through test tube then MS.

Chickens - detected that chickens were being fed with died food instead of the corn that is supposed to give them their yellow colour

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Using the MS (HSW)

Radioactive Elements - the decay occurs when an unstable nucleus breaks up emitting (A,B or G), thorium-228 to radium-224.

In radioactive isotope the one constant factor is the time it takes for half of the material to decay called HALF-LIFE. (Uranium, Radium and Plutonium)

Radio Active Dating - radiocarbon dating is a technique (carbon-14) dead sea scrolls and the iceman are two well known examples.

Drug Testing - performance enhancers have been detected ANABOLIC STEROIDS (Floyd Landis) not always accurate though.

Mass Spec in space - to identify different elements in space (He, molecular N2 and CO2) US Space station rely on it for undetected elements to tell astronauts (NASA).

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Deciphering Electronic Structure of an Atom (HSW)

Thomson's Plum Pudding Model - negative electrons embedded in the sphere of positive ones explaining the behaviour of matter.

Rutherford's Atom with a Nucleus - directing a beam of alpha particles at thin metal foils, most passed through but some were deflected. He proposed that the mass of an atom was a positively charged region surrounded by electrons, there was an electrostatic repulsion between the A particles and metal nucleus.

Bohr's Electron Shells - if gas is heated an electrical passes through it giving out light, passing it through a prism grid deflects the line spectrum (identical for elements). They were arranged in shells of different energy levels. His idea fitted for H2, could not explain the more than one atom (Quantum Mechanics).

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Energy Levels and Electron Shells

Principal Quantum Number - number assigned to electron shells, showing size of shell and distance from nucleus

Ionisation - the re movement of an electron from an atom (endothermic)

An atom at ground state is at its lowest energy - hydrogen is 1312 kJ mol-1

The easier it is to remove the electron the more reactive the substance - calculating the 'total energy required': FI + SI

Shell - shell 1 requires the most energy as it is the closest to the nucleus

Orbitals - region were electron is more likely to be found

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Electron Spin - rotation of electrons C/AC creating a magnetic field

Two electrons on the same orbital cannot have the same spin

Hund's Rule - electrons placed in a set of orbitals with equal energy spread out to maximise the number of unpaired electrons.

Electron Density Maps - P orbitals are dumb belled shaped and lie at 90

Periodic table trends - the NBG have a full outer shell so the have high ionisation energies

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Blocks of the Periodic Table

S block - Grp 1/2 electrons are easily lost to form positive ions, consists of METALS (Na, K, Ca, Mg) which are very reactive, forming stable ionic compounds. Low M/BT and densities. He and H+ are also Sblock but...

D block - between Grp 2/3 Transition Metals (Cu, Fe, Ag, Cr) much less reactive than Grp 1/2 because inner D orbital is being filled whilst S stays full, conduct electricity and heat Mercury - liquid at room temp

F block - top row (lanthanide) similar metals, second row (actinides) radioactive - up to uranium are radioactive, others synthesised and made stable but with half lives.

P block - Grp 3/4/5/6/7/8 contains non metals and metalloid/some metals. Tin and Pb form +ions. Post-transition metals are non-reactive. Metalloid are the diagonal block Si/Ge have been responsible for microchip revolution. COVALENT Bonds non-metal/NM, some forms of carbon conduct electricity Grp 8 extremely non reactive due to full shells

HSW - heavier noble gases will make compounds xenonhexafluoroplantinate a powerful OA

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Trends in the Periodic Table

Across the PT electron number increases, down the PT more shells.

Atomic Radius increases across a period - nuclear charge becomes more positive n.o. protons increases. e- number increases but all in the same shell attracted to the nucleus more reducing ATOMIC RADIUS

Atomic Radius increases down a group - outer electrons enter new energy levels don group, although nucleus gains pos protons e- further away so more shells, so the are not held as close together.

Atomic radius changes when atoms form ions, pos ion always has a smaller AR - due to loss of e- so greater share of pos+.

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I think revision card 9 may be wrong. I thought that atomic radius DECREASES across a period because electrons are added within the same shell so they are pulled closer towards the nucleus.

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