A-LEVEL AQA ChEMISTRY NOTES
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- In the Periodic Table, elements are arranged in order of increasing atomic number
- Elements can be grouped into periods (horizontal rows) and groups (vertical columns).
- Periodicity is a regularly repeating pattern of atomic, physical, and chemical properties with increasing atomic number
- The Periodic Table can be split into s-, p-, d-, and f- blocks. Which is determined by which orbital the highest energy electron is in.
- Across period 3, the trend in meting point relates to the structure of the elements. The melting point increases from Na to Al as the ionic charge and the number of delocalised electrons increases. Silicon has a giant covalent structure with strong covalent bonds. P4, S8, and Cl2 are all simple molecular covalent substances. From P4 to S8 there are more electrons and stronger London forces. From S8 to Cl2 to Ar there are fewer electrons and weaker London forces.
- Across the period, the atomic radius decreases as effective nuclear charge increases and there is no increase in shelving.
- Across the period, the ionisation energy increases as nuclear charge increases.
- Aluminium is an exception as the 3s electrons shield the 3p electron
- Sulfur is an exception as an electron is being removed from an p orbital containing 2 electrons, so there is electron-pair repulsion