Chemistry/Y4/The Periodic Table





Definitions of Key Terms

 * Electrostatic Attraction / Coulomb Force - The force that binds atoms and electrons together, due to their opposite charges. It can be approximated as $$ E = q_{1}q_{2}/ r^2 $$, where q1 and q2 represents the charge in the electron and the nucleus and r is the distance between the electron and the nucleus.
 * Actual Nuclear Charge (Z) - The proton number of atom. It is the total charge of all the protons in the atom, i.e. the total positive charge that attracts all of the electrons in the atom.
 * Shielding Electrons (S) - The number of electrons not in the valence shell (outer shell) of the atom. Electrons in the inner shells of the atom exert a repulsive force on the electrons in the outer/valence shell, i.e. they shield the valence electrons from the attractive force of the positive nuclear charge.
 * Effective Nuclear Charge (Zeff) - Resultant positive charge acting on a valence shell electron, after taking into account the repulsive force by the electrons in the inner shell. $$Z_{eff} = Z - S$$. (Note that Eeff is not the same as electrostatic force E, it is only the positive charge of the nucleus, q. To calculate the actual electrostatic force E, the distance r has to be taken into account as well, as shown in the equation above.)
 * First Ionisation Energy (1st I.E.) - Measure of energy (usually in kJ/mol) required to remove one mole of electrons from one mole of X (g), where X is an element (atom or molecule) in gaseous form.

Acknowledgements

 * Jeremy Teoh (2010) - RI Year 4 Chemistry Speed Revision Notes v2