Topic 1 - Atomic Structure and Periodic Table

• The mass of an electron is 1/1840
• An orbital is a region within the atom that can hold up to 2 electrons with opposite spins
• An S orbital is spherical and can hold up to 2 electrons
• A P orbital is a dumbell-shape that can hold up to 6 electrons
• A D orbital is complex shaped and can hold up to 12 electrons
• Hund's rule is that electron will occupy orbitals of the same energy singly before filling
• Pauli exclusion principle states that electrons can not occupy the same orbital unless they have opposite spins
• 4s is found between 3p and 3d
• Relative atomic mass is the weighted mean mass of an atom of an element compared to 1/12 of Carbon-12
• Relative isotopic mass is the mass of an individual atom of a particular isotope relative to 1/12 of Carbon-12
• Mass spectrometry only works on ions
• Periodicity is the regular repeating pattern of atomic, physical and chemical properties with increasing atomic number
• Atomic radius is the distance from the centre of the nucleus to the boundary of the electron cloud
• Atomic radius will decrease across a period as atomic number increases, positive proton mass increases so the attraction is stronger, and electron shells are not added
• Atomic radius decreases down a group as electron shells are added, shielding increases more significantly than the increasing proton mass and attractiveness
• Ionisation is when an electron gains enough energy for it to lose attraction to the nucleus
• The first ionisation energy is the energy required to remove an electron from each atom in one mole of atoms in the gaseous state
• The equation for the first ionisation energy is:

  $Fe_(g) → Fe_(g)^+$$+$$e^-$
• When there is a huge increase in ionisation energy, it means it has moved onto the next quantum shell
• Ionisation energy increases across a period because there is a stronger nuclear charge so electrons will be more attracted to the nucleus
• Ionisation energy decreases down a group, whilst nuclear charge does increase, electron shells are added (creating more shielding) and electrons are further away from the nucleus, making them less attracted
• Ionisation energy slightly decreases between magnesium and aluminium because electrons move onto the p orbital and there is slightly more repulsion
• Ionisation energy slightly decreases between phosphorus and sulfur because electrons begin to pair up, resulting in more repulsion
• The d orbital holds 10 electrons
• Atomic radius decreases across a period because nuclear charge increases so electrons are more attracted, bringing them close to the nucleus
• Atomic radius increases down a group because additional shells are added, creating more shielding between the electrons and the nucleus