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HKDSE Chemistry – Microscopic World I

HKDSE Chemistry Core
Section 2: Microscopic World I | 微觀世界 I

Billy Sir’s Smart Notes: Master Atomic Structure, Chemical Bonding, and the 4 Giant/Simple Structures.
由資深導師 Billy Sir 編寫，助你極速掌握原子結構、化學鍵及四大結構與性質。

1. Atomic Structure & Isotopes | 原子結構與同位素

An atom consists of a central nucleus (containing protons and neutrons) surrounded by electrons in electron shells. 原子由中心的原子核（包含質子和中子）及外圍電子層中的電子組成。

🔬 Isotopes | 同位素

Isotopes are different atoms of the same element that have the same number of protons but a different number of neutrons. 同位素是具有相同質子數，但中子數不同的同種元素原子。

  • They have the same chemical properties because they have the same electronic arrangement. (它們具有相同的化學性質，因為電子排佈相同。)
  • They have different physical properties (e.g., density, mass) due to different numbers of neutrons. (由於中子數不同，它們的物理性質如密度、質量會有所不同。)
$$ \text{Relative Atomic Mass} = \sum \left( \text{Isotopic Mass} \times \text{Relative Abundance \%} \right) $$

2. Electronic Arrangement & Periodic Table | 電子排佈與週期表

The arrangement of electrons in an atom determines its position in the Periodic Table and its chemical behavior. 原子中電子的排佈決定了它在週期表中的位置及其化學行為。

  • Period (週期): The horizontal rows. The period number equals the number of occupied electron shells.
    橫行。週期數等於已佔用的電子層數。
  • Group (族): The vertical columns. The group number equals the number of outermost shell (valence) electrons.
    直行。族數等於最外層（價）電子數。

Example: Sodium (Na) has an atomic number of 11. Its electronic arrangement is 2, 8, 1. Therefore, it is in Period 3 and Group I. (例子：鈉的原子序為11，電子排佈為 2, 8, 1。因此它位於第3週期、第I族。)

3. Chemical Bonding | 化學鍵

Atoms bond together to achieve a stable noble gas electronic arrangement (octet or duplet). 原子透過鍵結來達到穩定的貴氣體電子排佈（八隅體或雙電子）。

Bond Type (鍵型) Formation (形成方式) Nature of Attraction (引力本質)
Ionic Bond
離子鍵		 Transfer of electrons from metal to non-metal.
電子由金屬轉移至非金屬。		 Strong electrostatic attraction between oppositely charged ions.
帶相反電荷離子間的強大靜電引力。
Covalent Bond
共價鍵		 Sharing of outermost electrons between non-metals.
非金屬之間共用最外層電子。		 Strong electrostatic attraction between shared electrons and two nuclei.
共用電子與兩個原子核間的強大靜電引力。
Metallic Bond
金屬鍵		 Metal atoms lose outer electrons to form a “sea of electrons”.
金屬原子失去外層電子形成「電子海」。		 Strong electrostatic attraction between positive metal ions and delocalized electrons.
金屬陽離子與離域電子間的強大靜電引力。

4. Structures and Properties | 結構與性質

⚠️ Exam Trap: Bonding vs. Structure | 考試陷阱：化學鍵 vs 結構

Never confuse “Bonding” (the glue) with “Structure” (the 3D arrangement). For example, water (\(H_2O\)) has covalent bonds between H and O atoms, but its overall structure is a simple molecular structure. When boiling water, we break the weak intermolecular forces, NOT the strong covalent bonds! 千萬不要混淆「化學鍵」（黏合劑）和「結構」（立體排列）。例如，水分子內有共價鍵，但整體是簡單分子結構。沸騰時，我們打破的是微弱的分子間引力，而不是強大的共價鍵！

Structure (結構) Examples (例子) Melting & Boiling Point (熔點及沸點) Electrical Conductivity (導電性)
Giant Ionic Structure
巨型離子結構		 \( \text{NaCl} \), \( \text{MgO} \) High: A lot of heat is needed to overcome strong ionic bonds.
高：需大量熱能克服強大的離子鍵。		 Molten/Aqueous only: Mobile ions are present. Solid state has no mobile ions.
僅在熔融/水溶液態導電：有流動離子。
Giant Covalent Structure
巨型共價結構		 Diamond (鑽石), Quartz (\( \text{SiO}_2 \)) Very High: A lot of heat is needed to break the extensive network of strong covalent bonds.
極高：需大量熱能打破龐大的共價鍵網絡。		 Non-conductor: No mobile electrons/ions. (Exception: Graphite conducts due to delocalized electrons)
不導電：無流動電子/離子。(石墨例外)
Giant Metallic Structure
巨型金屬結構		 \( \text{Fe} \), \( \text{Cu} \) High: A lot of heat is needed to overcome strong metallic bonds.
高：需大量熱能克服強大的金屬鍵。		 Good conductor (All states): Contains a “sea” of delocalized mobile electrons.
優良導體(所有狀態)：含有流動的離域電子。
Simple Molecular Structure
簡單分子結構		 \( \text{H}_2\text{O} \), \( \text{CO}_2 \), \( \text{I}_2 \) Low: Only a little heat is needed to overcome the weak intermolecular forces (Van der Waals’ forces).
低：只需少量熱能克服微弱的分子間引力。		 Non-conductor: Molecules are neutral and have no mobile electrons or ions.
不導電：分子呈中性，無流動電子或離子。

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