Chapter 8: The Periodic Table — Part 1

Topic 8.1–8.2, 8.5 · Arrangement, Group I, and noble gases

The Periodic Table Arrangement

The Periodic Table is used to classify elements and predict their properties.
Elements are arranged in order of increasing atomic (proton) number, in horizontal rows called periods, and vertical columns called groups.
Electronic Configuration: Elements in the same group have the same number of outer shell electrons, which results in similar chemical properties.
The number of outer shell electrons is equal to the group number (for Groups I to VII), and the number of occupied electron shells is equal to the period number.
Metallic and Non-Metallic Character: Metals are found on the left, and non-metals are toward the top right. Metallic character (the tendency to lose electrons) increases down a group and decreases across a period.
Group Number and Ion Charge: Elements in Groups I, II, and III (metals) lose electrons to form positive ions with charges of +1, +2, and +3 respectively. Elements in Groups V, VI, and VII (non-metals) gain electrons to form negative ions with charges of -3, -2, and -1.

Exam Traps

Do not confuse period number with group number — sodium (2,8,1) is Period 3, Group I.

Group I elements (lithium, sodium, and potassium) are relatively soft metals that can be cut with a knife.
Trends down the group:
- Decreasing melting point: The strength of metallic bonds decreases, requiring less energy to break.
- Increasing density: While density increases, Group I elements generally have low densities and will float on water.
- Increasing reactivity: Reactivity increases because atomic radius and electron shielding increase down the group, meaning the outer electron is less strongly attracted to the nucleus and is lost more easily.
These trends allow for the prediction of properties of other Group I elements (e.g., rubidium and caesium), which would be expected to be even softer and more reactive.

Exam Traps

Lithium reacts less vigorously with water than sodium — do not treat all alkali metals identically.

Group VIII elements (e.g., Argon, Neon) are unreactive, monatomic gases.
Stability: They are inert because they possess full outer shells of electrons (8 electrons, except Helium which has 2).
Because they have a stable electronic configuration, they do not need to lose or gain electrons, making them very stable and unreactive.

Exam Traps

Helium has 2 outer electrons, not 8 — do not apply the eight-electron rule to helium.

0/15

Ad Banner Placeholder