8. The Periodic Table (Part 1) (1/2) (Cambridge IGCSE Chemistry 0620 for 2023, 2024 & 2025)

Introduction to the Periodic Table

• The periodic table organizes all chemical elements to predict their physical properties and chemical reactions.

Arrangement of the Periodic Table

• Elements are arranged in:

  • Rows (Periods): horizontal arrangements.

  • Columns (Groups): vertical arrangements.

• Atomic Number: Number of protons in an element, displayed near each symbol.

• Order of arrangement:

  • Increasing proton number from left to right across periods.

  • Increasing atomic number from top to bottom down groups.

Periods

• Periods are numbered from 1 to 7.

• Period number indicates the number of electron shells in an atom.

• Example: Lithium (atomic number 3) has electron configuration 2, 1 - belongs to period 2.

• Period 2 elements (like oxygen) have two electron shells; period 3 elements (like sodium) have three.

Transition from Metals to Non-Metals

• Moving from left to right across a period:

  • Elements change from metallic characteristics to non-metallic characteristics.

• Distinct Line in the Periodic Table:

  • Red stepped line separates metals (left) from non-metals (right), with hydrogen as an exception.

Properties of Metals

• Characteristics:

  • Tend to lose electrons to form positive ions.

  • Good conductors of heat and electricity.

  • Shiny appearance, malleable, ductile.

  • High melting and boiling points.

Properties of Non-Metals

• Characteristics:

  • Tend to gain or share electrons to form negative ions or covalent bonds.

  • Poor conductors of heat and electricity.

  • Dull appearance, brittle in solid form.

  • Generally low melting and boiling points.

Groups

• Vertical columns indicate the number of outer electrons:

  • Group One Example: Lithium (atomic number 3), with an outer shell electron configuration of 2, 1, indicating it belongs to group one.

  • General Rule: Each group has a corresponding number of outer electrons.

• Exceptions: Group eight (or group zero) elements have full outer shells with 2 (He) or 8 (Ne, Ar, etc.) electrons.

Group Number and Ion Charge

• Group number determines edge of elements and their charge when forming ions:

  • Elements in groups 1-3 form positive ions (cations).

    • Group 1: 1 electron --> +1 ion (e.g., Na⁺)

    • Group 2: 2 electrons --> +2 ions (e.g., Ca²⁺)

    • Group 3: 3 electrons --> +3 ions (e.g., Al³⁺)

• Elements in groups 5-7 form negative ions (anions).

  • Group 5: 3 electrons --> -3 ion (e.g., N³⁻)

  • Group 6: 2 electrons --> -2 ions (e.g., O²⁻)

  • Group 7: 1 electron --> -1 ion (e.g., Cl⁻)

• Group zero: Full outer shell; stable, do not form ions easily.

Similar Properties within Groups

• Chemical properties depend on outer electrons.

• Elements in the same group exhibit similar chemical properties due to the same outer electron configuration.

• Example: Group one elements react similarly with water based on having one outer shell electron.

Predicting Properties from the Periodic Table

• The periodic table shows patterns or trends:

  • Includes boiling point, melting point, density, and reactivity.

• Example of Reactivity in Group One:

  • Trend: Reactivity increases down the group.

  • Lithium reacts slowly, sodium reacts vigorously, potassium expected to be more reactive than both.

Observing Trends in Group One Metals

• Reactivity Trend:

  • As you go down group one, reactivity increases:

    • Lithium: slow reaction with water, fizzing.

    • Sodium: more vigorous than lithium.

    • Potassium: reacts even more vigorously, burns with lilac flame.

    • Below potassium, rubidium reacts very violently, cesium explodes.

• Conclusion: Lower group metals are more reactive than those at the top.

Conclusion

• The periodic table helps understand the behavior and properties of elements based on their position.