Knowledge Organiser: The Periodic Table
Key Terms
- Group: Vertical column, same outer electrons
- Period: Horizontal row, same number of shells
- Metal: Left/centre, conducts, forms + ions
- Non-metal: Right, poor conductor
- Atomic number: Basis for ordering
Must-Know Facts
- Group = number of outer shell electrons
- Period = number of occupied shells
- Same group = same outer electrons = similar properties
- Group 1: reactivity increases down
- Group 7: reactivity decreases down
- Group 0: full outer shell, unreactive
- Ordered by atomic number, NOT atomic mass
Key Equations
- Group number = number of outer shell electrons
- Period number = number of occupied electron shells
- Atomic number = proton number (ordering principle)
Common Mistakes
- Saying the table is ordered by atomic mass: Mendeleev used mass, but the modern table is ordered by atomic number (proton number)
- Confusing group and period trends: Group 1 reactivity increases DOWN; Group 7 reactivity decreases DOWN
- Saying metals are only on the left: Transition metals occupy the large central block too
- Forgetting Group 0 is unreactive: Full outer shell = stable = won't form ions or bonds under normal conditions
Memory Aid
- Groups = Families: Elements in the same group are like family members — they share the same "personality" (chemical properties) because they have the same number of outer electrons.
- Periods = School Years: Moving across a period is like moving through a school year — you progress from the most metallic elements on the left to non-metals, finishing with the noble gas "graduation" at the end.
- Reactivity trends mnemonic: "Group 1 Goes Up (reactivity increases down), Group 7 Goes Down (reactivity decreases down)" — think of them as opposites.