The Periodic Table

1. History

• Development: The periodic table was developed over many years with contributions from different scientists.
• Dmitri Mendeleev: A Russian scientist who arranged the table by mass numbers and properties. In reality, the periodic table should be arranged by increasing atomic number.

2. Structure

• Periods: Horizontal rows of elements in the periodic table.
• Groups: Vertical columns of elements in the periodic table.

3. Group 1 (Alkali Metals)

• Electron Configuration: All have one electron in their outer orbit.
• Reactivity: Very reactive because atoms strive to have 8 electrons in their outer orbit. Reactivity increases down the group as atoms get bigger. Properties of Alkali Metals

Physical Properties:

• Soft and easily cut.
• Very reactive with water (must be stored under oil).

4. Group 2 (Alkaline Earth Metals)

• Electron Configuration: All elements in this group have 2 electrons in their outer orbit.

5. Group 7 (Halogens)

• Electron Configuration: All elements in this group have 7 electrons in their outer orbit.
• Reactivity: Very reactive.

6. Group 8 (Noble Gases)

• Electron Configuration: All elements have 8 electrons in their outer orbit.
• Reactivity: Very un-reactive and therefore stable.

7. Electron Configuration

Rules:

• 1st orbit: 2 electrons.
• 2nd orbit: 8 electrons.
• 3rd orbit: 8 electrons.
• 4th orbit: 16 electrons.

8. The Octet Rule

• Stability: Atoms aim to have a full outer orbit to be stable.
• Reactivity: Atoms without a full outer orbit will react with other elements.
• Noble Gases: Group 8 elements are un-reactive because they have full outer orbits.