OCR As level Chemistry- Periodicity

Periodicity is the recurring [blank_start]trends[blank_end] in the [blank_start]physical[blank_end] and chemical [blank_start]properties[blank_end] of the elements across each [blank_start]period[blank_end].

The first periodic table in the 1870's was created by [blank_start]Mendeleev[blank_end]

Reading from left to right, the elements are arranged in order of increasing [blank_start]atomic number[blank_end].

The chemistry of each element is determined by its [blank_start]electronic configuration[blank_end], particularly the outer, [blank_start]highest energy[blank_end] electron shell.

Ionisation energy measures how [blank_start]easily[blank_end] an atom [blank_start]loses electrons[blank_end] to form [blank_start]positive[blank_end] ions.

The first ionisation energy is the [blank_start]energy required[blank_end] to remove [blank_start]one electron[blank_end] from [blank_start]one mole[blank_end] of [blank_start]gaseous atoms[blank_end] to form one mole of [blank_start]gaseous ions[blank_end].

The [blank_start]greater[blank_end] the distance from the nucleus and the [blank_start]outer electrons[blank_end], the [blank_start]less[blank_end] the nuclear attraction.

The more [blank_start]protons[blank_end] there are in the nucleus of the atom, the [blank_start]greater[blank_end] the attraction between the [blank_start]nucleus[blank_end] and the electrons.

The second ionisation energy is the energy required to remove 1 electron from 1 mole of [blank_start]gaseous ions[blank_end] to form one mole of [blank_start]gaseous 2+ ions[blank_end].

As you go down a group: - the atomic radius [blank_start]increases[blank_end] - more inner shells so [blank_start]shielding increases[blank_end] - [blank_start]nuclear attraction[blank_end] decreases - first ionisation energy [blank_start]decreases[blank_end]

As you go across a period: - [blank_start]nuclear charge[blank_end] increases - same shell so [blank_start]similar[blank_end] shielding - nuclear attraction [blank_start]increases[blank_end] - atomic radius [blank_start]decreases[blank_end] - first ionisation energy [blank_start]increases[blank_end]

The fall in ionisation energy from beryllium to boron is due to the start of the [blank_start]filling[blank_end] of the [blank_start]2p[blank_end] sub-shell.

The fall in ionisation energy from nitrogen to oxygen is due to the start of [blank_start]electron pairing[blank_end] in the p orbitals of the [blank_start]2p[blank_end] sub-shell. The paired electrons [blank_start]repel[blank_end] each other which makes it [blank_start]easier[blank_end] to remove an electron. Nitrogen has [blank_start]half-shell[blank_end] stability.

Metallic bonding is the strong [blank_start]electrostatic[blank_end] attraction between [blank_start]delocalised[blank_end] electrons and positively charged [blank_start]cations.[blank_end]

Across period 2 and 3, the melting point [blank_start]increases[blank_end] between group [blank_start]1to 4[blank_end] where there is a sharp [blank_start]decrease[blank_end] between groups 4 and 5. The melting points of group 5 to 8 are all [blank_start]low[blank_end].