AS Chemistry Unit 1 Periodic Trends

AS Chemistry Unit 1 Periodic Trends

1. Nuclear Charge

   • Increases across a period as there are more electrons being added to the outer shells.
   • The nuclear charge of a group is the same because in a group they all have the same number of electrons on their outer shells.

2. Atomic Radius

   • Increases down a group because more shells are being added to the atom making the radius bigger.
   • Decreases across a period because the electron attraction is increasing, pulling the electrons closer together.

3. Electron Shielding

   • Stays the same across a period as the electrons are being put in the same shell.
   • Increases down a group as more shells are added.

4. Nuclear Attraction

   • Increases across a period because the atomic radius gets smaller and the nuclear charge increases.
   • Decreases down a group due to the increased atomic radius, so there is more shielding.

5. Ionisation Energy

   • Decreases down a group because the atomic radius increases therefore the electron shielding increases so the nuclear attraction decreases.
   • Increases across a period because the atomic radius decreases therefore the nuclear attraction is increasing, this makes it harder to remove an electron.

6. Melting and Boiling Points

   • Giant Metallic Lattice
     • High Boiling and Melting Point that increases with charge (1+ to 3+)
   • Giant Covalent Lattice
     • High Boiling and Melting Point
   • Simple Molecular Structures
     • Low Boiling and Melting Point that increases with the amount of molecules it attracts (e.g Oxygen being diatomic (O2)).
   • Period 3 Example

7. Periodic Table

   • Arranged in order of the number of protons (atomic number)
   • 7 Periods
   • 8 Groups

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