F331 Revision

Topics: Atom, Energy, Electron Pages: 5 (1350 words) Published: April 26, 2015
AS Chemistry Revision-Chemistry for Life
1. Avagadro constant, 6.02 x 10²³
number of particles in 1 mole of a substance

2. Empirical formula-simplest ratio of atoms of each element in a compound

3.

4. Model of an atom
Particle
Mass on relative atomic scale
Charge
Proton
1
1+
Neutron
1
0
Electron
Very small (0.00055)
1-

5. Radioactive isotopes
Radiation
What is it?
Relative charge
How does the nucleus change?
Stopped by?
Deflection in electric field?
Alpha α
Helium nuclei
⁴₂He
+2
2 fewer protons
2 fewer neutrons
Paper or skin
Low
Beta β
Electrons
₋₁°e
-1
1 more proton
1 fewer neutron
Aluminium foil
High
Gamma ϒ
Electromagnetic radiation
none
No change
Lead sheet
None

6.
Half-life
i. The time taken for half a radioactive isotope/substance to decay. ii. Not affected my temperature
iii. Can be used to date archaeological artefacts made from living things Tracers
i. Radioactive isotopes whose decay is monitored
ii. Can be used to aid diagnosis, followed by a Geiger counter iii. An isotope should have a half-life which is neither too short or it will decay before tracing is complete. nor too long or it will persist for too long in the body, potentially causing harm to the patient. 7. Absorption spectra

Coloured background with black lines
Lines go up
Lines get closer at higher frequency
Produced when:
i. Electrons absorb a photon (package of energy) and become excited. ii. Excited electrons move to a higher energy state- they are promoted iii. The electromagnetic radiation absorbed by each atom has a definite frequency related to the difference in energy levels by ∆E = hv

8. Emission spectra
Black background with coloured lines
Lines go down
Lines get closer at higher frequency
Produced when:
i. Electrons first absorb a photon and become excited
ii. Excited electrons move up to higher energy level
iii. Electrons drop back to lower energy level and emit electromagnetic radiation iv. The electromagnetic radiation emitted by an atom has a definite frequency related to the difference in energy levels by ∆E = hv

9. Properties
Structure
Type of bonding
Melting point
Solubility in water
Electrical conductivity
Ionic lattice
Ionic
high
Usually soluble
Only if molten or in solution
Giant covalent network
covalent
high
insoluble
Wont conduct, apart from graphite
Simple molecular
covalent
Low
Usually soluble
Wont conduct
Metallic lattice
Metallic
high
insoluble
Will conduct

10. Shapes of molecules-Electron densities repel each other as far as possible in space to minimise repulsion 6 groups of electrons – octahedral-90°

5 groups of electrons – trigonal bipyramidal-90°/120°

4 groups of electrons:
i. 4 bonding pairs ­– tetrahedral- 109°
ii. 3 bonding pairs and 1 lone pair – pyramidal- 109°
iii. 2 bonding pairs and 2 lone pairs – bent- 109°

3 groups of electrons – planar triangular - 120°

2 groups of electrons – linear - 180°

11. Reactions of group 2 elements
Metal + water metal hydroxide + hydrogen
Metal oxide + water metal hydroxide

Metal hydroxide + acid Salt + water
Hydroxides are more soluble down the group
Metal oxide + acid salt + water

Metal carbonate metal oxide + carbon dioxide
Thermal stability increases down the group .i.e BaCO₃ is less likely to break down on heating than MgCO₃ 12. Heterogeneous catalyst
Are in different physical state to the reactants
Work by:
i. The reactants are absorbed onto the catalyst surface
ii. Bonds between the reactants are weakened and broken
iii. New bonds and compounds are formed
iv. The products formed diffuse off the catalyst surface
Catalyst poison:
i. Poison is strongly absorbed onto the catalyst surface
ii. The poison blocks the catalyst surface, preventing reactants from bonding.

13. Mass spectrometer
Sample inlet-
Ionisation area- electrons produced by a heated filament...
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