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TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Chemistry > General Equations and Definitions

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• 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
(beta) decay	A neutron decomposes to create a electron and proton, the electron is then expelled from the nucleus
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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