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Revision:General Equations and Definitions
TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Chemistry > General Equations and Definitions
- Atomic Masses = the number of protons and neutrons
- Atomic Number = number of protons and therefore also the number electrons
- Electron Shielding = This is where electrons in the inner shells of a atom stop the full charge of the nucleus effect electrons outside that shell, e.g. if a shell has 6 electrons it will reduce the effective nuclear charge by 6+.
- Enthalpy = This is the energy change of a substance per mole.
| Particles in the atom | Charge in Coulombs | Mass in Kg | Relative Charge | Relative mass |
| P proton | 1.602 x 10–9 | 1.672 x 10-27 | +1 | 1 |
| N neutron | 0 | 1.675 x 10-27 | 0 | 1 |
| E electron | 1.602 x 10–9 | 9.109 x 10-31 | -1 | 1/1836 |
- Energy Transfer = Mass ´ Specific heat capacity ´Temperature change
- Energy Transferred = M x C x DT
- For enthalpy divide by the number of moles.
- Concentration = moles / volume
- Working out formula by percentage using RAM, divide the percentage by the RAM, E.g. for 22.02% of Carbon(12), 4.59% of hydrogen(1), 73.39% of Bromide(80): we get:
- 22.02 / 12 = ~ 2; 4.59 / 1= ~ 5; 73.39 / 80 = ~ 1 \ C2 H5 Br
- At 20°C; 1 mole of gas will occupy 24 dm3, this is the R.T.P.
- At 0°C; 1 mole of gas will occupy 22.414 dm3, this is the S.T.P.
- Moles = Mass / RAM
Radioactive Decay
| Radio Active Decay | Basically what happens | Example |
 (alpha ) decay
| The release of a helium nucleus (2 P and 2N) from the nucleus | 
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 (beta) decay
| A neutron decomposes to create a electron and proton, the electron is then expelled from the nucleus | 
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 Gamma Decay
| The nucleus has too much energy, which makes it unstable, so a pulse of energy is expelled from the nucleus | - |
| Fission | Where a large atom decomposes into two smaller atoms and sometimes some other neutrons are released | 
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