Electrons and bonding
Describe the number of electrons that can fill the first four shells.
1st shell = 2 2nd shell = 8 3rd shell = 18 4th shell = 32
Define atomic regions / orbitals.
A region around the nucleus that can hold up to two electrons, with opposite spins.
Describe the shape of s and p orbitals, the number of orbitals each shell holds and which each block in the periodic table is.
S orbitals are spherical, p orbitals are figure of eight shaped.
* An s sub-shell consists of a single s orbital.
* A p sub-shell consists of three p orbitals.
* A d sub-shell consists of five d orbitals.
* An f sub-shell consists of seven d orbitals
Group 1 and 2 are s block. Group 3-12 are the D block. Group 3-18 are the S block
Write the sub-shell notation for Kr. (atomic number = 36)
Note: 4s2 is filled before 3d10 however is written afterwards to reflect shell order.
Note: Alternatively, the electronic configuration could be written as a noble gas and then the additional electrons added after. E.g. (Ar) 4s1 is the sub-shell notation for potassium.
Why do electrons fill orbitals with the same energy occupation singly before pairing?
Due to charge repulsion electrons only pair when forced to, preferring to fill orbitals singly first.
Define the first ionisation energy.
The first ionisation energy of an element is the energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.
Define the successive ionisation energies.
Successive ionisation energy is a measure of the energy required to remove each electron in turn. An element has as many ionisation energies as it has electrons.
Give the three factors that ionisation energies depend on.
Increasing the atomic radius increases the distance between the nucleus and the outermost electrons. This reduces the attractive force, therefore I.E decreases. Increasing the number of protons in the nucleus increases the attractive force, therefore I.E. increases. Electrons in filled inner shells repel electrons in the outer shell and reduce the effect of the positive nuclear charge. An increasing number of inner shell electrons therefore increased Shielding. The overall attractive force experienced by the outer electrons decreases and therefore I.E. decreases.
Describe the arrow in box thing.
Orbitals are often represented as boxes (or lines) and electrons as arrows. In a pair, the arrows must point in opposite directions (up / down) to represent the opposite spins of the electrons. Where possible, electrons occupy orbitals singly (due to charge repulsion). Only when more electrons are present than the orbitals can hold singly, the electrons pair up (spin-pairing).